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class="vector-toc-list"> <li id="toc-Axial_skeleton" class="vector-toc-list-item vector-toc-level-2"> <a class="vector-toc-link" href="#Axial_skeleton"> <div class="vector-toc-text"> <span class="vector-toc-numb">1.1</span> <span>Axial skeleton</span> </div> </a> <ul id="toc-Axial_skeleton-sublist" class="vector-toc-list"> <li id="toc-Vertebral_column" class="vector-toc-list-item vector-toc-level-3"> <a class="vector-toc-link" href="#Vertebral_column"> <div class="vector-toc-text"> <span class="vector-toc-numb">1.1.1</span> <span>Vertebral column</span> </div> </a> <ul id="toc-Vertebral_column-sublist" class="vector-toc-list"> <li id="toc-Cervical_vertebrae" class="vector-toc-list-item vector-toc-level-4"> <a class="vector-toc-link" href="#Cervical_vertebrae"> <div class="vector-toc-text"> <span class="vector-toc-numb">1.1.1.1</span> <span>Cervical vertebrae</span> </div> </a> <ul id="toc-Cervical_vertebrae-sublist" class="vector-toc-list"> </ul> </li> <li id="toc-Thoracic_vertebrae" class="vector-toc-list-item vector-toc-level-4"> <a class="vector-toc-link" href="#Thoracic_vertebrae"> <div class="vector-toc-text"> <span class="vector-toc-numb">1.1.1.2</span> <span>Thoracic vertebrae</span> </div> </a> <ul id="toc-Thoracic_vertebrae-sublist" class="vector-toc-list"> </ul> </li> <li id="toc-Synsacrum" class="vector-toc-list-item vector-toc-level-4"> <a class="vector-toc-link" href="#Synsacrum"> <div class="vector-toc-text"> <span class="vector-toc-numb">1.1.1.3</span> <span>Synsacrum</span> </div> </a> <ul id="toc-Synsacrum-sublist" class="vector-toc-list"> </ul> </li> <li id="toc-Caudal_vertebrae" class="vector-toc-list-item vector-toc-level-4"> <a class="vector-toc-link" href="#Caudal_vertebrae"> <div class="vector-toc-text"> <span class="vector-toc-numb">1.1.1.4</span> <span>Caudal vertebrae</span> </div> </a> <ul id="toc-Caudal_vertebrae-sublist" class="vector-toc-list"> </ul> </li> <li id="toc-Pygostyle" class="vector-toc-list-item vector-toc-level-4"> <a class="vector-toc-link" href="#Pygostyle"> <div class="vector-toc-text"> <span class="vector-toc-numb">1.1.1.5</span> <span>Pygostyle</span> </div> </a> <ul id="toc-Pygostyle-sublist" class="vector-toc-list"> </ul> </li> </ul> </li> <li id="toc-Scapular_girdle" class="vector-toc-list-item vector-toc-level-3"> <a class="vector-toc-link" href="#Scapular_girdle"> <div class="vector-toc-text"> <span class="vector-toc-numb">1.1.2</span> <span>Scapular girdle</span> </div> </a> <ul id="toc-Scapular_girdle-sublist" class="vector-toc-list"> </ul> </li> <li id="toc-Ribs" class="vector-toc-list-item vector-toc-level-3"> <a class="vector-toc-link" href="#Ribs"> <div class="vector-toc-text"> <span class="vector-toc-numb">1.1.3</span> <span>Ribs</span> </div> </a> <ul id="toc-Ribs-sublist" class="vector-toc-list"> </ul> </li> <li id="toc-Skull" class="vector-toc-list-item vector-toc-level-3"> <a class="vector-toc-link" href="#Skull"> <div class="vector-toc-text"> <span class="vector-toc-numb">1.1.4</span> <span>Skull</span> </div> </a> <ul id="toc-Skull-sublist" class="vector-toc-list"> </ul> </li> </ul> </li> <li id="toc-Appendicular_skeleton" class="vector-toc-list-item vector-toc-level-2"> <a class="vector-toc-link" href="#Appendicular_skeleton"> <div class="vector-toc-text"> <span class="vector-toc-numb">1.2</span> <span>Appendicular skeleton</span> </div> </a> <ul id="toc-Appendicular_skeleton-sublist" class="vector-toc-list"> <li id="toc-Wings" class="vector-toc-list-item vector-toc-level-3"> <a class="vector-toc-link" href="#Wings"> <div class="vector-toc-text"> <span class="vector-toc-numb">1.2.1</span> <span>Wings</span> </div> </a> <ul id="toc-Wings-sublist" class="vector-toc-list"> </ul> </li> <li id="toc-Feet" class="vector-toc-list-item vector-toc-level-3"> <a class="vector-toc-link" href="#Feet"> <div class="vector-toc-text"> <span class="vector-toc-numb">1.2.2</span> <span>Feet</span> </div> </a> <ul id="toc-Feet-sublist" class="vector-toc-list"> </ul> </li> </ul> </li> <li id="toc-Evolution" class="vector-toc-list-item vector-toc-level-2"> <a class="vector-toc-link" href="#Evolution"> <div class="vector-toc-text"> <span class="vector-toc-numb">1.3</span> <span>Evolution</span> </div> </a> <ul id="toc-Evolution-sublist" class="vector-toc-list"> <li id="toc-Hind_limb_change" class="vector-toc-list-item vector-toc-level-3"> <a class="vector-toc-link" href="#Hind_limb_change"> <div class="vector-toc-text"> <span class="vector-toc-numb">1.3.1</span> <span>Hind limb change</span> </div> </a> <ul id="toc-Hind_limb_change-sublist" class="vector-toc-list"> </ul> </li> <li id="toc-Forelimb_changes" class="vector-toc-list-item vector-toc-level-3"> <a class="vector-toc-link" href="#Forelimb_changes"> <div class="vector-toc-text"> <span class="vector-toc-numb">1.3.2</span> <span>Forelimb changes</span> </div> </a> <ul id="toc-Forelimb_changes-sublist" class="vector-toc-list"> </ul> </li> </ul> </li> </ul> </li> <li id="toc-Muscular_system" class="vector-toc-list-item vector-toc-level-1"> <a class="vector-toc-link" href="#Muscular_system"> <div class="vector-toc-text"> <span class="vector-toc-numb">2</span> <span>Muscular system</span> </div> </a> <ul id="toc-Muscular_system-sublist" class="vector-toc-list"> </ul> </li> <li id="toc-Integumentary_system" class="vector-toc-list-item vector-toc-level-1"> <a class="vector-toc-link" href="#Integumentary_system"> <div class="vector-toc-text"> <span class="vector-toc-numb">3</span> <span>Integumentary system</span> </div> </a> <button aria-controls="toc-Integumentary_system-sublist" class="cdx-button cdx-button--weight-quiet cdx-button--icon-only vector-toc-toggle"> <span class="vector-icon mw-ui-icon-wikimedia-expand"></span> <span>Toggle Integumentary system subsection</span> </button> <ul id="toc-Integumentary_system-sublist" class="vector-toc-list"> <li id="toc-Scales" class="vector-toc-list-item vector-toc-level-2"> <a class="vector-toc-link" href="#Scales"> <div class="vector-toc-text"> <span class="vector-toc-numb">3.1</span> <span>Scales</span> </div> </a> <ul id="toc-Scales-sublist" class="vector-toc-list"> </ul> </li> <li id="toc-Herbst_corpuscles_and_lore" class="vector-toc-list-item vector-toc-level-2"> <a class="vector-toc-link" href="#Herbst_corpuscles_and_lore"> <div class="vector-toc-text"> <span class="vector-toc-numb">3.2</span> <span>Herbst corpuscles and lore</span> </div> </a> <ul id="toc-Herbst_corpuscles_and_lore-sublist" class="vector-toc-list"> </ul> </li> <li id="toc-Beak" class="vector-toc-list-item vector-toc-level-2"> <a class="vector-toc-link" href="#Beak"> <div class="vector-toc-text"> <span class="vector-toc-numb">3.3</span> <span>Beak</span> </div> </a> <ul id="toc-Beak-sublist" class="vector-toc-list"> </ul> </li> </ul> </li> <li id="toc-Respiratory_system" class="vector-toc-list-item vector-toc-level-1"> <a class="vector-toc-link" href="#Respiratory_system"> <div class="vector-toc-text"> <span class="vector-toc-numb">4</span> <span>Respiratory system</span> </div> </a> <ul id="toc-Respiratory_system-sublist" class="vector-toc-list"> </ul> </li> <li id="toc-Circulatory_system" class="vector-toc-list-item vector-toc-level-1"> <a class="vector-toc-link" href="#Circulatory_system"> <div class="vector-toc-text"> <span class="vector-toc-numb">5</span> <span>Circulatory system</span> </div> </a> <ul id="toc-Circulatory_system-sublist" class="vector-toc-list"> </ul> </li> <li id="toc-Digestive_system" class="vector-toc-list-item vector-toc-level-1"> <a class="vector-toc-link" href="#Digestive_system"> <div class="vector-toc-text"> <span class="vector-toc-numb">6</span> <span>Digestive system</span> </div> </a> <button aria-controls="toc-Digestive_system-sublist" class="cdx-button cdx-button--weight-quiet cdx-button--icon-only vector-toc-toggle"> <span class="vector-icon mw-ui-icon-wikimedia-expand"></span> <span>Toggle Digestive system subsection</span> </button> <ul id="toc-Digestive_system-sublist" class="vector-toc-list"> <li id="toc-Crop" class="vector-toc-list-item vector-toc-level-2"> <a class="vector-toc-link" href="#Crop"> <div class="vector-toc-text"> <span class="vector-toc-numb">6.1</span> <span>Crop</span> </div> </a> <ul id="toc-Crop-sublist" class="vector-toc-list"> </ul> </li> <li id="toc-Proventriculus" class="vector-toc-list-item vector-toc-level-2"> <a class="vector-toc-link" href="#Proventriculus"> <div class="vector-toc-text"> <span class="vector-toc-numb">6.2</span> <span>Proventriculus</span> </div> </a> <ul id="toc-Proventriculus-sublist" class="vector-toc-list"> </ul> </li> <li id="toc-Gizzard" class="vector-toc-list-item vector-toc-level-2"> <a class="vector-toc-link" href="#Gizzard"> <div class="vector-toc-text"> <span class="vector-toc-numb">6.3</span> <span>Gizzard</span> </div> </a> <ul id="toc-Gizzard-sublist" class="vector-toc-list"> </ul> </li> <li id="toc-Intestines" class="vector-toc-list-item vector-toc-level-2"> <a class="vector-toc-link" href="#Intestines"> <div class="vector-toc-text"> <span class="vector-toc-numb">6.4</span> <span>Intestines</span> </div> </a> <ul id="toc-Intestines-sublist" class="vector-toc-list"> </ul> </li> <li id="toc-Drinking_behaviour" class="vector-toc-list-item vector-toc-level-2"> <a class="vector-toc-link" href="#Drinking_behaviour"> <div class="vector-toc-text"> <span class="vector-toc-numb">6.5</span> <span>Drinking behaviour</span> </div> </a> <ul id="toc-Drinking_behaviour-sublist" class="vector-toc-list"> </ul> </li> </ul> </li> <li id="toc-Reproductive_and_urogenital_systems" class="vector-toc-list-item vector-toc-level-1"> <a class="vector-toc-link" href="#Reproductive_and_urogenital_systems"> <div class="vector-toc-text"> <span class="vector-toc-numb">7</span> <span>Reproductive and urogenital systems</span> </div> </a> <button aria-controls="toc-Reproductive_and_urogenital_systems-sublist" class="cdx-button cdx-button--weight-quiet cdx-button--icon-only vector-toc-toggle"> <span class="vector-icon mw-ui-icon-wikimedia-expand"></span> <span>Toggle Reproductive and urogenital systems subsection</span> </button> <ul id="toc-Reproductive_and_urogenital_systems-sublist" class="vector-toc-list"> <li id="toc-Kidney" class="vector-toc-list-item vector-toc-level-2"> <a class="vector-toc-link" href="#Kidney"> <div class="vector-toc-text"> <span class="vector-toc-numb">7.1</span> <span>Kidney</span> </div> </a> <ul id="toc-Kidney-sublist" class="vector-toc-list"> </ul> </li> </ul> </li> <li id="toc-Nervous_system" class="vector-toc-list-item vector-toc-level-1"> <a class="vector-toc-link" href="#Nervous_system"> <div class="vector-toc-text"> <span class="vector-toc-numb">8</span> <span>Nervous system</span> </div> </a> <button aria-controls="toc-Nervous_system-sublist" class="cdx-button cdx-button--weight-quiet cdx-button--icon-only vector-toc-toggle"> <span class="vector-icon mw-ui-icon-wikimedia-expand"></span> <span>Toggle Nervous system subsection</span> </button> <ul id="toc-Nervous_system-sublist" class="vector-toc-list"> <li id="toc-Brain" class="vector-toc-list-item vector-toc-level-2"> <a class="vector-toc-link" href="#Brain"> <div class="vector-toc-text"> <span class="vector-toc-numb">8.1</span> <span>Brain</span> </div> </a> <ul id="toc-Brain-sublist" class="vector-toc-list"> </ul> </li> <li id="toc-Vision" class="vector-toc-list-item vector-toc-level-2"> <a class="vector-toc-link" href="#Vision"> <div class="vector-toc-text"> <span class="vector-toc-numb">8.2</span> <span>Vision</span> </div> </a> <ul id="toc-Vision-sublist" class="vector-toc-list"> </ul> </li> <li id="toc-Hearing" class="vector-toc-list-item vector-toc-level-2"> <a class="vector-toc-link" href="#Hearing"> <div class="vector-toc-text"> <span class="vector-toc-numb">8.3</span> <span>Hearing</span> </div> </a> <ul id="toc-Hearing-sublist" class="vector-toc-list"> </ul> </li> <li id="toc-Taste" class="vector-toc-list-item vector-toc-level-2"> <a class="vector-toc-link" href="#Taste"> <div class="vector-toc-text"> <span class="vector-toc-numb">8.4</span> <span>Taste</span> </div> </a> <ul id="toc-Taste-sublist" class="vector-toc-list"> </ul> </li> </ul> </li> <li id="toc-Immune_system" class="vector-toc-list-item vector-toc-level-1"> <a class="vector-toc-link" href="#Immune_system"> <div class="vector-toc-text"> <span class="vector-toc-numb">9</span> <span>Immune system</span> </div> </a> <button aria-controls="toc-Immune_system-sublist" class="cdx-button cdx-button--weight-quiet cdx-button--icon-only vector-toc-toggle"> <span class="vector-icon mw-ui-icon-wikimedia-expand"></span> <span>Toggle Immune system subsection</span> </button> <ul id="toc-Immune_system-sublist" class="vector-toc-list"> <li id="toc-Bursa_of_Fabricius" class="vector-toc-list-item vector-toc-level-2"> <a class="vector-toc-link" href="#Bursa_of_Fabricius"> <div class="vector-toc-text"> <span class="vector-toc-numb">9.1</span> <span>Bursa of Fabricius</span> </div> </a> <ul id="toc-Bursa_of_Fabricius-sublist" class="vector-toc-list"> <li id="toc-Function" class="vector-toc-list-item vector-toc-level-3"> <a class="vector-toc-link" href="#Function"> <div class="vector-toc-text"> <span class="vector-toc-numb">9.1.1</span> <span>Function</span> </div> </a> <ul id="toc-Function-sublist" class="vector-toc-list"> </ul> </li> <li id="toc-Anatomy" class="vector-toc-list-item vector-toc-level-3"> <a class="vector-toc-link" href="#Anatomy"> <div class="vector-toc-text"> <span class="vector-toc-numb">9.1.2</span> <span>Anatomy</span> </div> </a> <ul id="toc-Anatomy-sublist" class="vector-toc-list"> </ul> </li> </ul> </li> </ul> </li> <li id="toc-See_also" class="vector-toc-list-item vector-toc-level-1"> <a class="vector-toc-link" href="#See_also"> <div class="vector-toc-text"> <span class="vector-toc-numb">10</span> <span>See also</span> </div> </a> <ul id="toc-See_also-sublist" class="vector-toc-list"> </ul> </li> <li id="toc-References" class="vector-toc-list-item vector-toc-level-1"> <a class="vector-toc-link" href="#References"> <div class="vector-toc-text"> <span class="vector-toc-numb">11</span> <span>References</span> </div> </a> <ul id="toc-References-sublist" class="vector-toc-list"> </ul> </li> <li id="toc-External_links" class="vector-toc-list-item vector-toc-level-1"> <a class="vector-toc-link" href="#External_links"> <div class="vector-toc-text"> <span class="vector-toc-numb">12</span> <span>External links</span> </div> </a> <ul id="toc-External_links-sublist" class="vector-toc-list"> </ul> </li> </ul> </div> </div> </nav> </div> </div> <div class="mw-content-container"> <main id="content" class="mw-body"> <header class="mw-body-header vector-page-titlebar"> <nav aria-label="Contents" class="vector-toc-landmark"> <div id="vector-page-titlebar-toc" class="vector-dropdown vector-page-titlebar-toc vector-button-flush-left" > <input type="checkbox" id="vector-page-titlebar-toc-checkbox" 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Available in 25 languages" > <label id="p-lang-btn-label" for="p-lang-btn-checkbox" class="vector-dropdown-label cdx-button cdx-button--fake-button cdx-button--fake-button--enabled cdx-button--weight-quiet cdx-button--action-progressive mw-portlet-lang-heading-25" aria-hidden="true" ><span class="vector-icon mw-ui-icon-language-progressive mw-ui-icon-wikimedia-language-progressive"></span> <span class="vector-dropdown-label-text">25 languages</span> </label> <div class="vector-dropdown-content"> <div class="vector-menu-content"> <ul class="vector-menu-content-list"> <li class="interlanguage-link interwiki-ar mw-list-item"><a href="https://ar.wikipedia.org/wiki/%D8%AA%D8%B4%D8%B1%D9%8A%D8%AD_%D8%A7%D9%84%D8%B7%D9%8A%D9%88%D8%B1" title="تشريح الطيور – Arabic" lang="ar" hreflang="ar" data-title="تشريح الطيور" data-language-autonym="العربية" data-language-local-name="Arabic" class="interlanguage-link-target"><span>العربية</span></a></li><li class="interlanguage-link interwiki-bg mw-list-item"><a href="https://bg.wikipedia.org/wiki/%D0%90%D0%BD%D0%B0%D1%82%D0%BE%D0%BC%D0%B8%D1%8F_%D0%BD%D0%B0_%D0%BF%D1%82%D0%B8%D1%86%D0%B8%D1%82%D0%B5" title="Анатомия на птиците – Bulgarian" lang="bg" hreflang="bg" data-title="Анатомия на птиците" data-language-autonym="Български" data-language-local-name="Bulgarian" class="interlanguage-link-target"><span>Български</span></a></li><li class="interlanguage-link interwiki-bs mw-list-item"><a href="https://bs.wikipedia.org/wiki/Anatomija_ptica" title="Anatomija ptica – Bosnian" lang="bs" hreflang="bs" data-title="Anatomija ptica" data-language-autonym="Bosanski" data-language-local-name="Bosnian" class="interlanguage-link-target"><span>Bosanski</span></a></li><li class="interlanguage-link interwiki-ca mw-list-item"><a href="https://ca.wikipedia.org/wiki/Anatomia_dels_ocells" title="Anatomia dels ocells – Catalan" lang="ca" hreflang="ca" data-title="Anatomia dels ocells" data-language-autonym="Català" data-language-local-name="Catalan" class="interlanguage-link-target"><span>Català</span></a></li><li class="interlanguage-link interwiki-cs mw-list-item"><a href="https://cs.wikipedia.org/wiki/Anatomie_pt%C3%A1k%C5%AF" title="Anatomie ptáků – Czech" lang="cs" hreflang="cs" data-title="Anatomie ptáků" data-language-autonym="Čeština" data-language-local-name="Czech" class="interlanguage-link-target"><span>Čeština</span></a></li><li class="interlanguage-link interwiki-el badge-Q17437796 badge-featuredarticle mw-list-item" title="featured article badge"><a href="https://el.wikipedia.org/wiki/%CE%91%CE%BD%CE%B1%CF%84%CE%BF%CE%BC%CE%B9%CE%BA%CE%AE_%CE%BA%CE%B1%CE%B9_%CF%86%CF%85%CF%83%CE%B9%CE%BF%CE%BB%CE%BF%CE%B3%CE%AF%CE%B1_%CF%80%CF%84%CE%B7%CE%BD%CF%8E%CE%BD" title="Ανατομική και φυσιολογία πτηνών – Greek" lang="el" hreflang="el" data-title="Ανατομική και φυσιολογία πτηνών" data-language-autonym="Ελληνικά" data-language-local-name="Greek" class="interlanguage-link-target"><span>Ελληνικά</span></a></li><li class="interlanguage-link interwiki-es mw-list-item"><a href="https://es.wikipedia.org/wiki/Anatom%C3%ADa_de_las_aves" title="Anatomía de las aves – Spanish" lang="es" hreflang="es" data-title="Anatomía de las aves" data-language-autonym="Español" data-language-local-name="Spanish" class="interlanguage-link-target"><span>Español</span></a></li><li class="interlanguage-link interwiki-eo mw-list-item"><a href="https://eo.wikipedia.org/wiki/Birdanatomio" title="Birdanatomio – Esperanto" lang="eo" hreflang="eo" data-title="Birdanatomio" data-language-autonym="Esperanto" data-language-local-name="Esperanto" class="interlanguage-link-target"><span>Esperanto</span></a></li><li class="interlanguage-link interwiki-fa mw-list-item"><a href="https://fa.wikipedia.org/wiki/%DA%A9%D8%A7%D9%84%D8%A8%D8%AF%D8%B4%D9%86%D8%A7%D8%B3%DB%8C_%D9%BE%D8%B1%D9%86%D8%AF%DA%AF%D8%A7%D9%86" title="کالبدشناسی پرندگان – Persian" lang="fa" hreflang="fa" data-title="کالبدشناسی پرندگان" data-language-autonym="فارسی" data-language-local-name="Persian" class="interlanguage-link-target"><span>فارسی</span></a></li><li class="interlanguage-link interwiki-fr mw-list-item"><a href="https://fr.wikipedia.org/wiki/Anatomie_des_oiseaux" title="Anatomie des oiseaux – French" lang="fr" hreflang="fr" data-title="Anatomie des oiseaux" data-language-autonym="Français" data-language-local-name="French" class="interlanguage-link-target"><span>Français</span></a></li><li class="interlanguage-link interwiki-ga mw-list-item"><a href="https://ga.wikipedia.org/wiki/Anatama%C3%ADocht_na_n-%C3%A9an" title="Anatamaíocht na n-éan – Irish" lang="ga" hreflang="ga" data-title="Anatamaíocht na n-éan" data-language-autonym="Gaeilge" data-language-local-name="Irish" class="interlanguage-link-target"><span>Gaeilge</span></a></li><li class="interlanguage-link interwiki-gl mw-list-item"><a href="https://gl.wikipedia.org/wiki/Anatom%C3%ADa_das_aves" title="Anatomía das aves – Galician" lang="gl" hreflang="gl" data-title="Anatomía das aves" data-language-autonym="Galego" data-language-local-name="Galician" class="interlanguage-link-target"><span>Galego</span></a></li><li class="interlanguage-link interwiki-id mw-list-item"><a href="https://id.wikipedia.org/wiki/Anatomi_burung" title="Anatomi burung – Indonesian" lang="id" hreflang="id" data-title="Anatomi burung" data-language-autonym="Bahasa Indonesia" data-language-local-name="Indonesian" class="interlanguage-link-target"><span>Bahasa Indonesia</span></a></li><li class="interlanguage-link interwiki-it mw-list-item"><a href="https://it.wikipedia.org/wiki/Topografia_degli_uccelli" title="Topografia degli uccelli – Italian" lang="it" hreflang="it" data-title="Topografia degli uccelli" data-language-autonym="Italiano" data-language-local-name="Italian" class="interlanguage-link-target"><span>Italiano</span></a></li><li class="interlanguage-link interwiki-lt badge-Q17437798 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href="https://sr.wikipedia.org/wiki/%D0%90%D0%BD%D0%B0%D1%82%D0%BE%D0%BC%D0%B8%D1%98%D0%B0_%D0%BF%D1%82%D0%B8%D1%86%D0%B0" title="Анатомија птица – Serbian" lang="sr" hreflang="sr" data-title="Анатомија птица" data-language-autonym="Српски / srpski" data-language-local-name="Serbian" class="interlanguage-link-target"><span>Српски / srpski</span></a></li><li class="interlanguage-link interwiki-sv mw-list-item"><a href="https://sv.wikipedia.org/wiki/F%C3%A5glars_anatomi" title="Fåglars anatomi – Swedish" lang="sv" hreflang="sv" data-title="Fåglars anatomi" data-language-autonym="Svenska" data-language-local-name="Swedish" class="interlanguage-link-target"><span>Svenska</span></a></li><li class="interlanguage-link interwiki-ta mw-list-item"><a href="https://ta.wikipedia.org/wiki/%E0%AE%AA%E0%AE%B1%E0%AE%B5%E0%AF%88_%E0%AE%89%E0%AE%9F%E0%AE%B1%E0%AF%8D%E0%AE%95%E0%AF%82%E0%AE%B1%E0%AE%BF%E0%AE%AF%E0%AE%B2%E0%AF%8D" title="பறவை உடற்கூறியல் – Tamil" lang="ta" hreflang="ta" data-title="பறவை 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</div> </div> <div id="bodyContent" class="vector-body" aria-labelledby="firstHeading" data-mw-ve-target-container> <div class="vector-body-before-content"> <div class="mw-indicators"> </div> <div id="siteSub" class="noprint">From Wikipedia, the free encyclopedia</div> </div> <div id="contentSub"><div id="mw-content-subtitle"></div></div> <div id="mw-content-text" class="mw-body-content"><div class="mw-content-ltr mw-parser-output" lang="en" dir="ltr"><div class="shortdescription nomobile noexcerpt noprint searchaux" style="display:none">Anatomy of birds</div> <p><b>Bird anatomy</b>, or the <a href="/wiki/Physiology" title="Physiology">physiological structure</a> of <a href="/wiki/Bird" title="Bird">birds</a>' bodies, shows many unique adaptations, mostly aiding <a href="/wiki/Bird_flight" title="Bird flight">flight</a>. Birds have a light <a href="/wiki/Skeletal_system" class="mw-redirect" title="Skeletal system">skeletal system</a> and light but powerful <a href="/wiki/Musculature" class="mw-redirect" title="Musculature">musculature</a> which, along with <a href="/wiki/Circulatory" class="mw-redirect" title="Circulatory">circulatory</a> and <a href="/wiki/Respiratory_systems" class="mw-redirect" title="Respiratory systems">respiratory systems</a> capable of very high <a href="/wiki/Metabolic" class="mw-redirect" title="Metabolic">metabolic</a> rates and <a href="/wiki/Oxygen" title="Oxygen">oxygen</a> supply, permit the bird to fly. The development of a <a href="/wiki/Beak" title="Beak">beak</a> has led to <a href="/wiki/Evolution" title="Evolution">evolution</a> of a specially adapted <a href="/wiki/Digestion" title="Digestion">digestive system</a>. </p> <meta property="mw:PageProp/toc" /> <div class="mw-heading mw-heading2"><h2 id="Skeletal_system">Skeletal system</h2><span class="mw-editsection"><span class="mw-editsection-bracket">[</span><a href="/w/index.php?title=Bird_anatomy&action=edit&section=1" title="Edit section: Skeletal system"><span>edit</span></a><span class="mw-editsection-bracket">]</span></span></div> <figure class="mw-default-size" typeof="mw:File/Thumb"><a href="/wiki/File:Squelette_oiseau.svg" class="mw-file-description"><img src="//upload.wikimedia.org/wikipedia/commons/thumb/5/58/Squelette_oiseau.svg/220px-Squelette_oiseau.svg.png" decoding="async" width="220" height="293" class="mw-file-element" srcset="//upload.wikimedia.org/wikipedia/commons/thumb/5/58/Squelette_oiseau.svg/330px-Squelette_oiseau.svg.png 1.5x, //upload.wikimedia.org/wikipedia/commons/thumb/5/58/Squelette_oiseau.svg/440px-Squelette_oiseau.svg.png 2x" data-file-width="892" data-file-height="1188" /></a><figcaption>A stylised <a href="/wiki/Dove" class="mw-redirect" title="Dove">dove</a> skeleton. Key: <div><ol style="margin-left:0;"><li style="list-style-position:inside;"><a href="/wiki/Skull" title="Skull">skull</a></li><li style="list-style-position:inside;"><a href="/wiki/Cervical_vertebrae" title="Cervical vertebrae">cervical vertebrae</a></li><li style="list-style-position:inside;"><a href="/wiki/Furcula" title="Furcula">furcula</a></li><li style="list-style-position:inside;"><a href="/wiki/Coracoid" title="Coracoid">coracoid</a></li><li style="list-style-position:inside;"><a href="/wiki/Uncinate_processes_of_ribs" title="Uncinate processes of ribs">uncinate processes of ribs</a></li><li style="list-style-position:inside;"><a href="/wiki/Keel_(bird)" class="mw-redirect" title="Keel (bird)">keel</a></li><li style="list-style-position:inside;"><a href="/wiki/Patella" title="Patella">patella</a></li><li style="list-style-position:inside;"><a href="/wiki/Tarsometatarsus" title="Tarsometatarsus">tarsometatarsus</a></li><li style="list-style-position:inside;"><a href="/wiki/Digit_(anatomy)" title="Digit (anatomy)">digits</a></li><li style="list-style-position:inside;"><a href="/wiki/Tibia" title="Tibia">tibia</a> (<a href="/wiki/Tibiotarsus" title="Tibiotarsus">tibiotarsus</a>)</li><li style="list-style-position:inside;"><a href="/wiki/Fibula" title="Fibula">fibula</a> (<a href="/wiki/Tibiotarsus" title="Tibiotarsus">tibiotarsus</a>)</li><li style="list-style-position:inside;"><a href="/wiki/Femur" title="Femur">femur</a></li><li style="list-style-position:inside;"><a href="/wiki/Ischium" title="Ischium">ischium</a> (<a href="/wiki/Hip_bone" title="Hip bone">innominate</a>)</li><li style="list-style-position:inside;"><a href="/wiki/Pubis_(bone)" title="Pubis (bone)">pubis</a> (innominate)</li><li style="list-style-position:inside;"><a href="/wiki/Ilium_(bone)" title="Ilium (bone)">ilium</a> (innominate)</li><li style="list-style-position:inside;"><a href="/wiki/Caudal_vertebrae" title="Caudal vertebrae">caudal vertebrae</a></li><li style="list-style-position:inside;"><a href="/wiki/Pygostyle" title="Pygostyle">pygostyle</a></li><li style="list-style-position:inside;"><a href="/wiki/Synsacrum" title="Synsacrum">synsacrum</a></li><li style="list-style-position:inside;"><a href="/wiki/Scapula" title="Scapula">scapula</a></li><li style="list-style-position:inside;"><a href="/wiki/Dorsal_vertebrae" class="mw-redirect" title="Dorsal vertebrae">dorsal vertebrae</a></li><li style="list-style-position:inside;"><a href="/wiki/Humerus" title="Humerus">humerus</a></li><li style="list-style-position:inside;"><a href="/wiki/Ulna" title="Ulna">ulna</a></li><li style="list-style-position:inside;"><a href="/wiki/Radius_(bone)" title="Radius (bone)">radius</a></li><li style="list-style-position:inside;"><a href="/wiki/Carpometacarpus" title="Carpometacarpus">Carpometacarpus</a></li><li style="list-style-position:inside;"><a href="/wiki/Digit_(anatomy)" title="Digit (anatomy)">Digit III</a></li><li style="list-style-position:inside;"><a href="/wiki/Digit_(anatomy)" title="Digit (anatomy)">Digit II</a></li><li style="list-style-position:inside;"><a href="/wiki/Digit_(anatomy)" title="Digit (anatomy)">Digit I</a> (<a href="/wiki/Alula" title="Alula">alula</a>)</li></ol></div></figcaption></figure><figure class="mw-halign-left" typeof="mw:File/Thumb"><a href="/wiki/File:Birdmorphology.svg" class="mw-file-description"><img src="//upload.wikimedia.org/wikipedia/commons/thumb/1/1d/Birdmorphology.svg/300px-Birdmorphology.svg.png" decoding="async" width="300" height="215" class="mw-file-element" srcset="//upload.wikimedia.org/wikipedia/commons/thumb/1/1d/Birdmorphology.svg/450px-Birdmorphology.svg.png 1.5x, //upload.wikimedia.org/wikipedia/commons/thumb/1/1d/Birdmorphology.svg/600px-Birdmorphology.svg.png 2x" data-file-width="600" data-file-height="430" /></a><figcaption><a href="/wiki/Surface_anatomy" title="Surface anatomy">External anatomy</a> (topography) of a typical bird: <style data-mw-deduplicate="TemplateStyles:r1184024115">.mw-parser-output .div-col{margin-top:0.3em;column-width:30em}.mw-parser-output .div-col-small{font-size:90%}.mw-parser-output .div-col-rules{column-rule:1px solid #aaa}.mw-parser-output .div-col dl,.mw-parser-output .div-col ol,.mw-parser-output .div-col ul{margin-top:0}.mw-parser-output .div-col li,.mw-parser-output .div-col dd{page-break-inside:avoid;break-inside:avoid-column}</style><div class="div-col" style="column-width: 8em;"><div><ol style="margin-left:0;"><li style="list-style-position:inside;">Beak</li><li style="list-style-position:inside;">Head</li><li style="list-style-position:inside;">Iris</li><li style="list-style-position:inside;">Pupil</li><li style="list-style-position:inside;">Mantle</li><li style="list-style-position:inside;">Lesser coverts</li><li style="list-style-position:inside;">Scapulars</li><li style="list-style-position:inside;">Coverts</li><li style="list-style-position:inside;">Tertials</li><li style="list-style-position:inside;">Rump</li><li style="list-style-position:inside;">Primaries</li><li style="list-style-position:inside;"><a href="/wiki/Cloaca#Birds" title="Cloaca">Vent</a></li><li style="list-style-position:inside;">Thigh</li><li style="list-style-position:inside;">Tibio-tarsal articulation</li><li style="list-style-position:inside;">Tarsus</li><li style="list-style-position:inside;">Feet</li><li style="list-style-position:inside;">Tibia</li><li style="list-style-position:inside;">Belly</li><li style="list-style-position:inside;">Flanks</li><li style="list-style-position:inside;">Breast</li><li style="list-style-position:inside;">Throat</li><li style="list-style-position:inside;">Wattle</li><li style="list-style-position:inside;">Eyestripe</li></ol></div></div></figcaption></figure><p>Birds have many bones that are hollow (<a href="/wiki/Skeletal_pneumaticity" title="Skeletal pneumaticity">pneumatized</a>) with criss-crossing <a href="/wiki/Strut" title="Strut">struts</a> or <a href="/wiki/Truss" title="Truss">trusses</a> for structural <a href="/wiki/Strength_of_materials" title="Strength of materials">strength</a>. The number of hollow bones varies among species, though large <a href="/wiki/Gliding_flight" title="Gliding flight">gliding and soaring birds</a> tend to have the most. Respiratory <a href="/wiki/Air_sacs" class="mw-redirect" title="Air sacs">air sacs</a> often form air pockets within the semi-hollow bones of the bird's skeleton.<sup id="cite_ref-ritchisong_1-0" class="reference"><a href="#cite_note-ritchisong-1"><span class="cite-bracket">[</span>1<span class="cite-bracket">]</span></a></sup> The bones of <a href="/wiki/Diving_bird" title="Diving bird">diving birds</a> are often less hollow than those of non-diving species. <a href="/wiki/Penguin" title="Penguin">Penguins</a>, <a href="/wiki/Loon" title="Loon">loons</a>,<sup id="cite_ref-Gier52_2-0" class="reference"><a href="#cite_note-Gier52-2"><span class="cite-bracket">[</span>2<span class="cite-bracket">]</span></a></sup> and <a href="/wiki/Puffin" title="Puffin">puffins</a> are without pneumatized bones entirely.<sup id="cite_ref-3" class="reference"><a href="#cite_note-3"><span class="cite-bracket">[</span>3<span class="cite-bracket">]</span></a></sup><sup id="cite_ref-Fastovsky05_4-0" class="reference"><a href="#cite_note-Fastovsky05-4"><span class="cite-bracket">[</span>4<span class="cite-bracket">]</span></a></sup> <a href="/wiki/Flightless_birds" class="mw-redirect" title="Flightless birds">Flightless birds</a>, such as <a href="/wiki/Ostriches" class="mw-redirect" title="Ostriches">ostriches</a> and <a href="/wiki/Emu" title="Emu">emus</a>, have pneumatized <a href="/wiki/Femurs" class="mw-redirect" title="Femurs">femurs</a><sup id="cite_ref-Bezuidenhout99_5-0" class="reference"><a href="#cite_note-Bezuidenhout99-5"><span class="cite-bracket">[</span>5<span class="cite-bracket">]</span></a></sup> and, in the case of the emu, pneumatized <a href="/wiki/Cervical_vertebrae" title="Cervical vertebrae">cervical vertebrae</a>.<sup id="cite_ref-Wedel03_6-0" class="reference"><a href="#cite_note-Wedel03-6"><span class="cite-bracket">[</span>6<span class="cite-bracket">]</span></a></sup> </p><div class="mw-heading mw-heading3"><h3 id="Axial_skeleton">Axial skeleton</h3><span class="mw-editsection"><span class="mw-editsection-bracket">[</span><a href="/w/index.php?title=Bird_anatomy&action=edit&section=2" title="Edit section: Axial skeleton"><span>edit</span></a><span class="mw-editsection-bracket">]</span></span></div> <p>The bird skeleton is highly <a href="/wiki/Adaptation" title="Adaptation">adapted</a> for <a href="/wiki/Flight" title="Flight">flight</a>. It is extremely lightweight but strong enough to withstand the <a href="/wiki/Stress_(physics)" class="mw-redirect" title="Stress (physics)">stresses</a> of taking off, flying, and landing. One key adaptation is the fusing of <a href="/wiki/Bone" title="Bone">bones</a> into single <a href="/wiki/Ossification" title="Ossification">ossifications</a>, such as the <a href="/wiki/Pygostyle" title="Pygostyle">pygostyle</a>. Because of this, birds usually have a smaller number of bones than other terrestrial vertebrates. Birds also lack teeth or even a true <a href="/wiki/Jaw" title="Jaw">jaw</a> and instead have a <a href="/wiki/Beak" title="Beak">beak</a>, which is far more lightweight. The beaks of many baby birds have a projection called an <a href="/wiki/Egg_tooth" title="Egg tooth">egg tooth</a>, which facilitates their exit from the <a href="/wiki/Amniotic_egg" class="mw-redirect" title="Amniotic egg">amniotic egg</a>. It falls off once the egg has been penetrated. </p> <figure class="mw-halign-left" typeof="mw:File/Thumb"><a href="/wiki/File:Diversity_of_Bird_Vertebrae.png" class="mw-file-description"><img src="//upload.wikimedia.org/wikipedia/commons/thumb/e/ed/Diversity_of_Bird_Vertebrae.png/246px-Diversity_of_Bird_Vertebrae.png" decoding="async" width="246" height="271" class="mw-file-element" srcset="//upload.wikimedia.org/wikipedia/commons/thumb/e/ed/Diversity_of_Bird_Vertebrae.png/369px-Diversity_of_Bird_Vertebrae.png 1.5x, //upload.wikimedia.org/wikipedia/commons/thumb/e/ed/Diversity_of_Bird_Vertebrae.png/491px-Diversity_of_Bird_Vertebrae.png 2x" data-file-width="2492" data-file-height="2748" /></a><figcaption>Collage of bird anatomical illustrations with the different vertebral sections color-coded across various species. The species included are as follows: <b>Top row (left to right)</b> <i><a href="/wiki/Common_ostrich" title="Common ostrich">Struthio camelus</a></i> and <i><a href="/wiki/Secretarybird" title="Secretarybird">Sagittarius serpentarius</a></i> (formerly <i>Gypogeranus serpentarius</i>) <b>Bottom row (left to right)</b> <i><a href="/wiki/Tropical_screech_owl" title="Tropical screech owl">Megascops choliba</a> decussatus</i> (formerly known as <i>Strix decussata</i>) and <i><a href="/wiki/Gyrfalcon" title="Gyrfalcon">Falco rusticolus</a> islandus</i> (formerly <i>Falco islandus</i>). <table class="wikitable"> <caption>Sections of the vertebral column in anatomical bird diagrams </caption> <tbody><tr> <th>Color </th> <th>Vertebral section </th></tr> <tr> <td>Pink </td> <td>Cervical vertebrae </td></tr> <tr> <td>Orange </td> <td>Thoracic/dorsal vertebrae </td></tr> <tr> <td>Yellow </td> <td>Synsacrum </td></tr> <tr> <td>Green </td> <td>Caudal vertebrae </td></tr> <tr> <td>Blue </td> <td>Pygostyle </td></tr></tbody></table> </figcaption></figure> <div class="mw-heading mw-heading4"><h4 id="Vertebral_column">Vertebral column</h4><span class="mw-editsection"><span class="mw-editsection-bracket">[</span><a href="/w/index.php?title=Bird_anatomy&action=edit&section=3" title="Edit section: Vertebral column"><span>edit</span></a><span class="mw-editsection-bracket">]</span></span></div> <p>The vertebral column is divided into five sections of <a href="/wiki/Vertebra" title="Vertebra">vertebrae</a>: </p> <div class="mw-heading mw-heading5"><h5 id="Cervical_vertebrae">Cervical vertebrae</h5><span class="mw-editsection"><span class="mw-editsection-bracket">[</span><a href="/w/index.php?title=Bird_anatomy&action=edit&section=4" title="Edit section: Cervical vertebrae"><span>edit</span></a><span class="mw-editsection-bracket">]</span></span></div> <p>The cervical vertebrae provide structural support to the neck and number between 8 and as many as 25 vertebrae in certain swan species (<a href="/wiki/Swan" title="Swan">Cygninae</a>) and other long-necked birds. All cervical vertebrae have transverse processes attached except the first one. This vertebra (C1) is called the atlas which articulates with the occipital condyles of the skull and lacks the foramen typical of most vertebrae.<sup id="cite_ref-:37_7-0" class="reference"><a href="#cite_note-:37-7"><span class="cite-bracket">[</span>7<span class="cite-bracket">]</span></a></sup> The neck of a bird is composed of many <a href="/wiki/Cervical_vertebrae" title="Cervical vertebrae">cervical vertebrae</a> enabling birds to have increased flexibility. A flexible neck allows many birds with immobile eyes to move their head more productively and center their sight on objects that are close or far in distance.<sup id="cite_ref-:2_8-0" class="reference"><a href="#cite_note-:2-8"><span class="cite-bracket">[</span>8<span class="cite-bracket">]</span></a></sup> Most birds have about three times as many neck vertebrae as humans, which allows for increased stability during fast movements such as flying, landing, and taking-off.<sup id="cite_ref-9" class="reference"><a href="#cite_note-9"><span class="cite-bracket">[</span>9<span class="cite-bracket">]</span></a></sup> The neck plays a role in head-bobbing which is present in at least 8 out of 27 orders of birds, including <a href="/wiki/Columbidae" title="Columbidae">Columbiformes</a>, <a href="/wiki/Galliformes" title="Galliformes">Galliformes</a>, and <a href="/wiki/Gruiformes" title="Gruiformes">Gruiformes</a>.<sup id="cite_ref-10" class="reference"><a href="#cite_note-10"><span class="cite-bracket">[</span>10<span class="cite-bracket">]</span></a></sup> Head-bobbing is an <a href="/wiki/Optokinetic_response" title="Optokinetic response">optokinetic response</a> which stabilizes a bird's surroundings as it alternates between a thrust phase and a hold phase.<sup id="cite_ref-:3_11-0" class="reference"><a href="#cite_note-:3-11"><span class="cite-bracket">[</span>11<span class="cite-bracket">]</span></a></sup> Head-bobbing is synchronous with the feet as the head moves in accordance with the rest of the body.<sup id="cite_ref-:3_11-1" class="reference"><a href="#cite_note-:3-11"><span class="cite-bracket">[</span>11<span class="cite-bracket">]</span></a></sup> Data from various studies suggest that the main reason for head-bobbing in some birds is for the stabilization of their surroundings, although it is uncertain why some but not all bird orders show head-bob.<sup id="cite_ref-:12_12-0" class="reference"><a href="#cite_note-:12-12"><span class="cite-bracket">[</span>12<span class="cite-bracket">]</span></a></sup> </p> <div class="mw-heading mw-heading5"><h5 id="Thoracic_vertebrae">Thoracic vertebrae</h5><span class="mw-editsection"><span class="mw-editsection-bracket">[</span><a href="/w/index.php?title=Bird_anatomy&action=edit&section=5" title="Edit section: Thoracic vertebrae"><span>edit</span></a><span class="mw-editsection-bracket">]</span></span></div><p> The thoracic vertebrae number between 5 and 10, and the first thoracic vertebra is distinguishable due to the fusion of its attached rib to the sternum while the ribs of cervical vertebrae are free.<sup id="cite_ref-:37_7-1" class="reference"><a href="#cite_note-:37-7"><span class="cite-bracket">[</span>7<span class="cite-bracket">]</span></a></sup> Anterior thoracic vertebrae are fused in many birds and articulate with the <a href="/wiki/Notarium" title="Notarium">notarium</a> of the pectoral girdle.<sup id="cite_ref-:13_13-0" class="reference"><a href="#cite_note-:13-13"><span class="cite-bracket">[</span>13<span class="cite-bracket">]</span></a></sup></p><figure class="mw-halign-left" typeof="mw:File/Thumb"><a href="/wiki/File:Bird_Pelvic_Girdle_Skeleton.png" class="mw-file-description"><img alt="Diagram of a general bird pelvic girdle skeleton including the lower vertebral column sections. The diagram includes the synsacrum, caudal, and pygostyle vertebrae. Note that the caudal vertebrae (5–10) are not fused in this diagram but can be in certain species." src="//upload.wikimedia.org/wikipedia/commons/thumb/6/6b/Bird_Pelvic_Girdle_Skeleton.png/247px-Bird_Pelvic_Girdle_Skeleton.png" decoding="async" width="247" height="191" class="mw-file-element" srcset="//upload.wikimedia.org/wikipedia/commons/thumb/6/6b/Bird_Pelvic_Girdle_Skeleton.png/371px-Bird_Pelvic_Girdle_Skeleton.png 1.5x, //upload.wikimedia.org/wikipedia/commons/thumb/6/6b/Bird_Pelvic_Girdle_Skeleton.png/494px-Bird_Pelvic_Girdle_Skeleton.png 2x" data-file-width="2697" data-file-height="2082" /></a><figcaption>Diagram of a general bird pelvic girdle skeleton including the lower vertebral column sections. Note that the caudal vertebrae (5–10) are not fused in this diagram but can be in certain species.</figcaption></figure> <div class="mw-heading mw-heading5"><h5 id="Synsacrum">Synsacrum</h5><span class="mw-editsection"><span class="mw-editsection-bracket">[</span><a href="/w/index.php?title=Bird_anatomy&action=edit&section=6" title="Edit section: Synsacrum"><span>edit</span></a><span class="mw-editsection-bracket">]</span></span></div> <p>The <a href="/wiki/Synsacrum" title="Synsacrum">synsacrum</a> consists of one thoracic, six lumbar, two sacral, and five sacro-caudal vertebrae fused into one ossified structure that then fuse with the ilium.<sup id="cite_ref-:23_14-0" class="reference"><a href="#cite_note-:23-14"><span class="cite-bracket">[</span>14<span class="cite-bracket">]</span></a></sup> When not in flight, this structure provides the main support for the rest of the body.<sup id="cite_ref-:37_7-2" class="reference"><a href="#cite_note-:37-7"><span class="cite-bracket">[</span>7<span class="cite-bracket">]</span></a></sup> Similar to the <a href="/wiki/Sacrum" title="Sacrum">sacrum</a> of mammals, the synsacrum lacks the distinct disc shape of cervical and thoracic vertebrae.<sup id="cite_ref-15" class="reference"><a href="#cite_note-15"><span class="cite-bracket">[</span>15<span class="cite-bracket">]</span></a></sup> </p> <div class="mw-heading mw-heading5"><h5 id="Caudal_vertebrae">Caudal vertebrae</h5><span class="mw-editsection"><span class="mw-editsection-bracket">[</span><a href="/w/index.php?title=Bird_anatomy&action=edit&section=7" title="Edit section: Caudal vertebrae"><span>edit</span></a><span class="mw-editsection-bracket">]</span></span></div> <p>The free vertebrae immediately following the fused sacro-caudal vertebrae of the synsacrum are known as the caudal vertebrae. Birds have between 5 and 8 free caudal vertebrae.<sup id="cite_ref-:37_7-3" class="reference"><a href="#cite_note-:37-7"><span class="cite-bracket">[</span>7<span class="cite-bracket">]</span></a></sup> The caudal vertebrae provide structure to the tails of vertebrates and are homologous to the <a href="/wiki/Coccyx" title="Coccyx">coccyx</a> found in mammals lacking tails.<sup id="cite_ref-16" class="reference"><a href="#cite_note-16"><span class="cite-bracket">[</span>16<span class="cite-bracket">]</span></a></sup> </p> <div class="mw-heading mw-heading5"><h5 id="Pygostyle">Pygostyle</h5><span class="mw-editsection"><span class="mw-editsection-bracket">[</span><a href="/w/index.php?title=Bird_anatomy&action=edit&section=8" title="Edit section: Pygostyle"><span>edit</span></a><span class="mw-editsection-bracket">]</span></span></div><p> In birds, the last 5 to 6 caudal vertebrae are fused to form the <a href="/wiki/Pygostyle" title="Pygostyle">pygostyle</a>.<sup id="cite_ref-:23_14-1" class="reference"><a href="#cite_note-:23-14"><span class="cite-bracket">[</span>14<span class="cite-bracket">]</span></a></sup> Some sources note that up to 10 caudal vertebrae may make up this fused structure. This structure provides an attachment point for tail feathers that aid in control of flight.<sup id="cite_ref-:37_7-4" class="reference"><a href="#cite_note-:37-7"><span class="cite-bracket">[</span>7<span class="cite-bracket">]</span></a></sup></p><figure class="mw-default-size" typeof="mw:File/Thumb"><a href="/wiki/File:Attached_keeled_sternum_of_a_dissected_pigeon.jpg" class="mw-file-description"><img src="//upload.wikimedia.org/wikipedia/commons/thumb/1/1b/Attached_keeled_sternum_of_a_dissected_pigeon.jpg/220px-Attached_keeled_sternum_of_a_dissected_pigeon.jpg" decoding="async" width="220" height="275" class="mw-file-element" srcset="//upload.wikimedia.org/wikipedia/commons/thumb/1/1b/Attached_keeled_sternum_of_a_dissected_pigeon.jpg/330px-Attached_keeled_sternum_of_a_dissected_pigeon.jpg 1.5x, //upload.wikimedia.org/wikipedia/commons/thumb/1/1b/Attached_keeled_sternum_of_a_dissected_pigeon.jpg/440px-Attached_keeled_sternum_of_a_dissected_pigeon.jpg 2x" data-file-width="534" data-file-height="667" /></a><figcaption>Highlighted in red is an intact keeled sternum of a dissected pigeon. In flying birds the sternum is enlarged for increased muscle attachment.</figcaption></figure> <div class="mw-heading mw-heading4"><h4 id="Scapular_girdle">Scapular girdle</h4><span class="mw-editsection"><span class="mw-editsection-bracket">[</span><a href="/w/index.php?title=Bird_anatomy&action=edit&section=9" title="Edit section: Scapular girdle"><span>edit</span></a><span class="mw-editsection-bracket">]</span></span></div> <p>Birds are the only living <a href="/wiki/Vertebrate" title="Vertebrate">vertebrates</a> to have <a href="/wiki/Furcula" title="Furcula">fused collarbones</a> and a <a href="/wiki/Keel_(bird_anatomy)" title="Keel (bird anatomy)">keeled breastbone</a>.<sup id="cite_ref-:02_17-0" class="reference"><a href="#cite_note-:02-17"><span class="cite-bracket">[</span>17<span class="cite-bracket">]</span></a></sup> The keeled sternum serves as an attachment site for the muscles used in flying or swimming.<sup id="cite_ref-:02_17-1" class="reference"><a href="#cite_note-:02-17"><span class="cite-bracket">[</span>17<span class="cite-bracket">]</span></a></sup> Flightless birds, such as <a href="/wiki/Common_ostrich" title="Common ostrich">ostriches</a>, lack a keeled sternum and have denser and heavier bones compared to birds that fly.<sup id="cite_ref-18" class="reference"><a href="#cite_note-18"><span class="cite-bracket">[</span>18<span class="cite-bracket">]</span></a></sup> Swimming birds have a wide sternum, walking birds have a long sternum, and flying birds have a sternum that is nearly equal in width and height.<sup id="cite_ref-19" class="reference"><a href="#cite_note-19"><span class="cite-bracket">[</span>19<span class="cite-bracket">]</span></a></sup> The chest consists of the <a href="/wiki/Furcula" title="Furcula">furcula</a> (wishbone) and <a href="/wiki/Coracoid" title="Coracoid">coracoid</a> (collar bone) which, together with the <a href="/wiki/Scapula" title="Scapula">scapula</a>, form the <a href="/wiki/Shoulder_girdle" title="Shoulder girdle">pectoral girdle</a>; the side of the chest is formed by the ribs, which meet at the sternum (mid-line of the chest).<sup id="cite_ref-:37_7-5" class="reference"><a href="#cite_note-:37-7"><span class="cite-bracket">[</span>7<span class="cite-bracket">]</span></a></sup> </p> <div class="mw-heading mw-heading4"><h4 id="Ribs">Ribs</h4><span class="mw-editsection"><span class="mw-editsection-bracket">[</span><a href="/w/index.php?title=Bird_anatomy&action=edit&section=10" title="Edit section: Ribs"><span>edit</span></a><span class="mw-editsection-bracket">]</span></span></div> <p>Birds have <a href="/wiki/Uncinate_processes_of_ribs" title="Uncinate processes of ribs">uncinate processes</a> on the ribs. These are hooked extensions of bone which help to strengthen the rib cage by overlapping with the rib behind them. This feature is also found in the tuatara (<i><a href="/wiki/Sphenodon" class="mw-redirect" title="Sphenodon">Sphenodon</a></i>). </p> <div class="mw-heading mw-heading4"><h4 id="Skull">Skull</h4><span class="mw-editsection"><span class="mw-editsection-bracket">[</span><a href="/w/index.php?title=Bird_anatomy&action=edit&section=11" title="Edit section: Skull"><span>edit</span></a><span class="mw-editsection-bracket">]</span></span></div> <figure class="mw-default-size" typeof="mw:File/Thumb"><a href="/wiki/File:Cr%C3%A1neoAve.svg" class="mw-file-description"><img src="//upload.wikimedia.org/wikipedia/commons/thumb/3/36/Cr%C3%A1neoAve.svg/220px-Cr%C3%A1neoAve.svg.png" decoding="async" width="220" height="129" class="mw-file-element" srcset="//upload.wikimedia.org/wikipedia/commons/thumb/3/36/Cr%C3%A1neoAve.svg/330px-Cr%C3%A1neoAve.svg.png 1.5x, //upload.wikimedia.org/wikipedia/commons/thumb/3/36/Cr%C3%A1neoAve.svg/440px-Cr%C3%A1neoAve.svg.png 2x" data-file-width="514" data-file-height="301" /></a><figcaption>The typical cranial anatomy of a bird. Pmx= premaxilla, M= maxilla, D= dentary, V= vomer, Pal= palatine, Pt= Pterygoid, Lc= Lacrimal</figcaption></figure> <p>The skull consists of five major bones: the frontal (top of head), parietal (back of head), premaxillary and nasal (top <a href="/wiki/Beak" title="Beak">beak</a>), and the mandible (bottom beak). The skull of a normal bird usually weighs about 1% of the bird's total body weight. The eye occupies a considerable amount of the skull and is surrounded by a <a href="/wiki/Sclerotic_ring" class="mw-redirect" title="Sclerotic ring">sclerotic eye-ring</a>, a ring of tiny bones. This characteristic is also seen in their reptile cousins. </p><p>Broadly speaking, avian skulls consist of many small, non-overlapping bones. <a href="/wiki/Heterochrony" title="Heterochrony">Pedomorphosis</a>, maintenance of the ancestral state in adults, is thought to have facilitated the evolution of the avian skull. In essence, adult bird skulls will resemble the juvenile form of their <a href="/wiki/Theropoda" title="Theropoda">theropod dinosaur</a> ancestors.<sup id="cite_ref-Bhul_2012_20-0" class="reference"><a href="#cite_note-Bhul_2012-20"><span class="cite-bracket">[</span>20<span class="cite-bracket">]</span></a></sup> As the avian lineage has progressed and as pedomorphosis has occurred, they have lost the <a href="/wiki/Postorbital_bone" title="Postorbital bone">postorbital bone</a> behind the eye, the ectopterygoid at the back of the palate, and teeth.<sup id="cite_ref-21" class="reference"><a href="#cite_note-21"><span class="cite-bracket">[</span>21<span class="cite-bracket">]</span></a></sup><sup id="cite_ref-:1_22-0" class="reference"><a href="#cite_note-:1-22"><span class="cite-bracket">[</span>22<span class="cite-bracket">]</span></a></sup> The <a href="/wiki/Palate" title="Palate">palate</a> structures have also become greatly altered with changes, mostly reductions, seen in the ptyergoid, palatine, and <a href="/wiki/Jugal_bone" title="Jugal bone">jugal</a> bones. A reduction in the adductor chambers has also occurred. <sup id="cite_ref-:1_22-1" class="reference"><a href="#cite_note-:1-22"><span class="cite-bracket">[</span>22<span class="cite-bracket">]</span></a></sup> These are all conditions seen in the juvenile form of their ancestors. The <a href="/wiki/Premaxilla" title="Premaxilla">premaxillary</a> bone has also <a href="/wiki/Hypertrophy" title="Hypertrophy">hypertrophied</a> to form the beak while the maxilla has become diminished, as suggested by both developmental<sup id="cite_ref-Bhul_2012_20-1" class="reference"><a href="#cite_note-Bhul_2012-20"><span class="cite-bracket">[</span>20<span class="cite-bracket">]</span></a></sup> and paleontological <sup id="cite_ref-23" class="reference"><a href="#cite_note-23"><span class="cite-bracket">[</span>23<span class="cite-bracket">]</span></a></sup> studies. This expansion into the beak has occurred in tandem with the loss of a functional hand and the developmental of a point at the front of the beak that resembles a "finger".<sup id="cite_ref-:1_22-2" class="reference"><a href="#cite_note-:1-22"><span class="cite-bracket">[</span>22<span class="cite-bracket">]</span></a></sup> The <a href="/wiki/Premaxilla" title="Premaxilla">premaxilla</a> is also known to play a large role in feeding behaviours in fish.<sup id="cite_ref-24" class="reference"><a href="#cite_note-24"><span class="cite-bracket">[</span>24<span class="cite-bracket">]</span></a></sup><sup id="cite_ref-25" class="reference"><a href="#cite_note-25"><span class="cite-bracket">[</span>25<span class="cite-bracket">]</span></a></sup> </p><p>The structure of the avian skull has important implications for their feeding behaviours. Birds show independent movement of the skull bones known as <a href="/wiki/Cranial_kinesis" title="Cranial kinesis">cranial kinesis</a>. Cranial kinesis in birds occurs in several forms, but all of the different varieties are all made possible by the anatomy of the skull. Animals with large, overlapping bones (including the ancestors of modern birds)<sup id="cite_ref-26" class="reference"><a href="#cite_note-26"><span class="cite-bracket">[</span>26<span class="cite-bracket">]</span></a></sup><sup id="cite_ref-wang2021_27-0" class="reference"><a href="#cite_note-wang2021-27"><span class="cite-bracket">[</span>27<span class="cite-bracket">]</span></a></sup><sup id="cite_ref-hu2019_28-0" class="reference"><a href="#cite_note-hu2019-28"><span class="cite-bracket">[</span>28<span class="cite-bracket">]</span></a></sup> have akinetic (non-kinetic) skulls.<sup id="cite_ref-29" class="reference"><a href="#cite_note-29"><span class="cite-bracket">[</span>29<span class="cite-bracket">]</span></a></sup><sup id="cite_ref-30" class="reference"><a href="#cite_note-30"><span class="cite-bracket">[</span>30<span class="cite-bracket">]</span></a></sup> For this reason it has been argued that the pedomorphic bird beak can be seen as an evolutionary innovation.<sup id="cite_ref-:1_22-3" class="reference"><a href="#cite_note-:1-22"><span class="cite-bracket">[</span>22<span class="cite-bracket">]</span></a></sup> </p><p>Birds have a <a href="/wiki/Diapsid" title="Diapsid">diapsid</a> skull, as in reptiles, with a pre-lachrymal fossa (present in some reptiles). The skull has a single <a href="/wiki/Occipital_condyles" title="Occipital condyles">occipital condyle</a>.<sup id="cite_ref-31" class="reference"><a href="#cite_note-31"><span class="cite-bracket">[</span>31<span class="cite-bracket">]</span></a></sup> </p> <div class="mw-heading mw-heading3"><h3 id="Appendicular_skeleton">Appendicular skeleton</h3><span class="mw-editsection"><span class="mw-editsection-bracket">[</span><a href="/w/index.php?title=Bird_anatomy&action=edit&section=12" title="Edit section: Appendicular skeleton"><span>edit</span></a><span class="mw-editsection-bracket">]</span></span></div> <style data-mw-deduplicate="TemplateStyles:r1251242444">.mw-parser-output .ambox{border:1px solid #a2a9b1;border-left:10px solid #36c;background-color:#fbfbfb;box-sizing:border-box}.mw-parser-output .ambox+link+.ambox,.mw-parser-output .ambox+link+style+.ambox,.mw-parser-output .ambox+link+link+.ambox,.mw-parser-output .ambox+.mw-empty-elt+link+.ambox,.mw-parser-output .ambox+.mw-empty-elt+link+style+.ambox,.mw-parser-output .ambox+.mw-empty-elt+link+link+.ambox{margin-top:-1px}html body.mediawiki .mw-parser-output .ambox.mbox-small-left{margin:4px 1em 4px 0;overflow:hidden;width:238px;border-collapse:collapse;font-size:88%;line-height:1.25em}.mw-parser-output .ambox-speedy{border-left:10px solid #b32424;background-color:#fee7e6}.mw-parser-output .ambox-delete{border-left:10px solid #b32424}.mw-parser-output .ambox-content{border-left:10px solid #f28500}.mw-parser-output .ambox-style{border-left:10px solid #fc3}.mw-parser-output .ambox-move{border-left:10px solid #9932cc}.mw-parser-output .ambox-protection{border-left:10px solid #a2a9b1}.mw-parser-output .ambox .mbox-text{border:none;padding:0.25em 0.5em;width:100%}.mw-parser-output .ambox .mbox-image{border:none;padding:2px 0 2px 0.5em;text-align:center}.mw-parser-output .ambox .mbox-imageright{border:none;padding:2px 0.5em 2px 0;text-align:center}.mw-parser-output .ambox .mbox-empty-cell{border:none;padding:0;width:1px}.mw-parser-output .ambox .mbox-image-div{width:52px}@media(min-width:720px){.mw-parser-output .ambox{margin:0 10%}}@media print{body.ns-0 .mw-parser-output .ambox{display:none!important}}</style><table class="box-More_citations_needed_section plainlinks metadata ambox ambox-content ambox-Refimprove" role="presentation"><tbody><tr><td class="mbox-image"><div class="mbox-image-div"><span typeof="mw:File"><a href="/wiki/File:Question_book-new.svg" class="mw-file-description"><img alt="" src="//upload.wikimedia.org/wikipedia/en/thumb/9/99/Question_book-new.svg/50px-Question_book-new.svg.png" decoding="async" width="50" height="39" class="mw-file-element" srcset="//upload.wikimedia.org/wikipedia/en/thumb/9/99/Question_book-new.svg/75px-Question_book-new.svg.png 1.5x, //upload.wikimedia.org/wikipedia/en/thumb/9/99/Question_book-new.svg/100px-Question_book-new.svg.png 2x" data-file-width="512" data-file-height="399" /></a></span></div></td><td class="mbox-text"><div class="mbox-text-span">This section <b>needs additional citations for <a href="/wiki/Wikipedia:Verifiability" title="Wikipedia:Verifiability">verification</a></b>.<span class="hide-when-compact"> Please help <a href="/wiki/Special:EditPage/Bird_anatomy" title="Special:EditPage/Bird anatomy">improve this article</a> by <a href="/wiki/Help:Referencing_for_beginners" title="Help:Referencing for beginners">adding citations to reliable sources</a> in this section. Unsourced material may be challenged and removed.</span> <span class="date-container"><i>(<span class="date">September 2018</span>)</i></span><span class="hide-when-compact"><i> (<small><a href="/wiki/Help:Maintenance_template_removal" title="Help:Maintenance template removal">Learn how and when to remove this message</a></small>)</i></span></div></td></tr></tbody></table> <p>The shoulder consists of the <a href="/wiki/Scapula" title="Scapula">scapula</a> (shoulder blade), <a href="/wiki/Coracoid" title="Coracoid">coracoid</a>, and <a href="/wiki/Humerus" title="Humerus">humerus</a> (upper arm). The humerus joins the <a href="/wiki/Radius_(bone)" title="Radius (bone)">radius</a> and <a href="/wiki/Ulna" title="Ulna">ulna</a> (forearm) to form the elbow. The <a href="/wiki/Carpal_bones" title="Carpal bones">carpus</a> and <a href="/wiki/Metacarpal_bones" title="Metacarpal bones">metacarpus</a> form the "wrist" and "hand" of the bird, and the digits are fused together. The bones in the wing are extremely light so that the bird can fly more easily. </p><p>The hips consist of the pelvis, which includes three major bones: the <a href="/wiki/Ilium_(bone)" title="Ilium (bone)">ilium</a> (top of the hip), <a href="/wiki/Ischium" title="Ischium">ischium</a> (sides of hip), and <a href="/wiki/Pubis_(bone)" title="Pubis (bone)">pubis</a> (front of the hip). These are fused into one (the <a href="/wiki/Hip_bone" title="Hip bone">innominate bone</a>). Innominate bones are evolutionary significant in that they allow birds to lay eggs. They meet at the <a href="/wiki/Acetabulum" title="Acetabulum">acetabulum</a> (hip socket) and articulate with the femur, which is the first bone of the hind limb. </p><p>The upper leg consists of the femur. At the knee joint, the femur connects to the <a href="/wiki/Tibiotarsus" title="Tibiotarsus">tibiotarsus</a> (shin) and <a href="/wiki/Fibula" title="Fibula">fibula</a> (side of lower leg). The <a href="/wiki/Tarsometatarsus" title="Tarsometatarsus">tarsometatarsus</a> forms the upper part of the foot, digits make up the toes. The leg bones of birds are the heaviest, contributing to a low center of gravity, which aids in flight. A bird's skeleton accounts for only about 5% of its total body weight. </p><p>They have a greatly elongate tetradiate <a href="/wiki/Pelvis" title="Pelvis">pelvis</a>, similar to some reptiles. The hind limb has an intra-tarsal joint found also in some reptiles. There is extensive fusion of the trunk vertebrae as well as fusion with the <a href="/wiki/Shoulder_girdle" title="Shoulder girdle">pectoral girdle</a>. </p> <div class="mw-heading mw-heading4"><h4 id="Wings">Wings</h4><span class="mw-editsection"><span class="mw-editsection-bracket">[</span><a href="/w/index.php?title=Bird_anatomy&action=edit&section=13" title="Edit section: Wings"><span>edit</span></a><span class="mw-editsection-bracket">]</span></span></div> <style data-mw-deduplicate="TemplateStyles:r1236090951">.mw-parser-output .hatnote{font-style:italic}.mw-parser-output div.hatnote{padding-left:1.6em;margin-bottom:0.5em}.mw-parser-output .hatnote i{font-style:normal}.mw-parser-output .hatnote+link+.hatnote{margin-top:-0.5em}@media print{body.ns-0 .mw-parser-output .hatnote{display:none!important}}</style><div role="note" class="hatnote navigation-not-searchable">Main article: <a href="/wiki/Bird_wings" class="mw-redirect" title="Bird wings">Bird wings</a></div> <div class="mw-heading mw-heading4"><h4 id="Feet">Feet</h4><span class="mw-editsection"><span class="mw-editsection-bracket">[</span><a href="/w/index.php?title=Bird_anatomy&action=edit&section=14" title="Edit section: Feet"><span>edit</span></a><span class="mw-editsection-bracket">]</span></span></div> <link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1236090951"><div role="note" class="hatnote navigation-not-searchable">Main article: <a href="/wiki/Bird_feet_and_legs" title="Bird feet and legs">Bird feet and legs</a></div> <figure class="mw-halign-left" typeof="mw:File/Thumb"><a href="/wiki/File:Bird-feets-en.svg" class="mw-file-description"><img src="//upload.wikimedia.org/wikipedia/commons/thumb/d/d7/Bird-feets-en.svg/200px-Bird-feets-en.svg.png" decoding="async" width="200" height="224" class="mw-file-element" srcset="//upload.wikimedia.org/wikipedia/commons/thumb/d/d7/Bird-feets-en.svg/300px-Bird-feets-en.svg.png 1.5x, //upload.wikimedia.org/wikipedia/commons/thumb/d/d7/Bird-feets-en.svg/400px-Bird-feets-en.svg.png 2x" data-file-width="512" data-file-height="573" /></a><figcaption>Four types of bird feet<br />(right foot diagrams)</figcaption></figure> <p><a href="/wiki/Bird_feet_and_legs" title="Bird feet and legs">Birds' feet</a> are classified as <a href="/wiki/Dactyly#In_birds" title="Dactyly">anisodactyl</a>, <a href="/wiki/Dactyly#In_birds" title="Dactyly">zygodactyl</a>, <a href="/wiki/Dactyly#In_birds" title="Dactyly">heterodactyl</a>, <a href="/wiki/Dactyly#In_birds" title="Dactyly">syndactyl</a> or <a href="/wiki/Dactyly#In_birds" title="Dactyly">pamprodactyl</a>.<sup id="cite_ref-Proctor&Lynch_32-0" class="reference"><a href="#cite_note-Proctor&Lynch-32"><span class="cite-bracket">[</span>32<span class="cite-bracket">]</span></a></sup> Anisodactyl is the most common arrangement of digits in birds, with three toes forward and one back. This is common in <a href="/wiki/Songbird" title="Songbird">songbirds</a> and other <a href="/wiki/Perching_bird" class="mw-redirect" title="Perching bird">perching birds</a>, as well as hunting birds like <a href="/wiki/Eagle" title="Eagle">eagles</a>, <a href="/wiki/Hawk" title="Hawk">hawks</a>, and <a href="/wiki/Falcon" title="Falcon">falcons</a>. </p><p>Syndactyly, as it occurs in birds, is like anisodactyly, except that the second and third toes (the inner and middle forward-pointing toes), or three toes, are fused together, as in the <a href="/wiki/Belted_kingfisher" title="Belted kingfisher">belted kingfisher</a> <i>Ceryle alcyon</i>. This is characteristic of <a href="/wiki/Coraciiformes" title="Coraciiformes">Coraciiformes</a> (<a href="/wiki/Kingfisher" title="Kingfisher">kingfishers</a>, <a href="/wiki/Bee-eater" title="Bee-eater">bee-eaters</a>, <a href="/wiki/Coraciidae" title="Coraciidae">rollers</a>, etc.). </p><p>Zygodactyl (from Greek <span title="Ancient Greek (to 1453)-language text"><span lang="grc">ζυγον</span></span>, a <a href="/wiki/Yoke" title="Yoke">yoke</a>) feet have two toes facing forward (digits two and three) and two back (digits one and four). This arrangement is most common in <a href="/wiki/Arboreal" class="mw-redirect" title="Arboreal">arboreal</a> species, particularly those that climb <a href="/wiki/Tree" title="Tree">tree</a> trunks or clamber through foliage. Zygodactyly occurs in the <a href="/wiki/Parrot" title="Parrot">parrots</a>, <a href="/wiki/Woodpecker" title="Woodpecker">woodpeckers</a> (including <a href="/wiki/Flicker_(bird)" class="mw-redirect" title="Flicker (bird)">flickers</a>), <a href="/wiki/Cuckoo" title="Cuckoo">cuckoos</a> (including <a href="/wiki/Geococcyx" class="mw-redirect" title="Geococcyx">roadrunners</a>), and some <a href="/wiki/Owl" title="Owl">owls</a>. Zygodactyl tracks have been found dating to 120–110 <a href="/wiki/Megaannum#SI_prefix_multipliers" class="mw-redirect" title="Megaannum">Ma</a> (early <a href="/wiki/Cretaceous" title="Cretaceous">Cretaceous</a>), 50 million years before the first identified zygodactyl fossils.<sup id="cite_ref-33" class="reference"><a href="#cite_note-33"><span class="cite-bracket">[</span>33<span class="cite-bracket">]</span></a></sup> </p><p>Heterodactyly is like zygodactyly, except that digits three and four point forward and digits one and two point back. This is found only in <a href="/wiki/Trogon" title="Trogon">trogons</a>, while pamprodactyl is an arrangement in which all four toes may point forward, or birds may rotate the outer two toes backward. It is a characteristic of <a href="/wiki/Swift_(bird)" title="Swift (bird)">swifts</a> (<a href="/wiki/Apodidae" class="mw-redirect" title="Apodidae">Apodidae</a>). </p> <div class="mw-heading mw-heading3"><h3 id="Evolution">Evolution</h3><span class="mw-editsection"><span class="mw-editsection-bracket">[</span><a href="/w/index.php?title=Bird_anatomy&action=edit&section=15" title="Edit section: Evolution"><span>edit</span></a><span class="mw-editsection-bracket">]</span></span></div> <div class="mw-heading mw-heading4"><h4 id="Hind_limb_change">Hind limb change</h4><span class="mw-editsection"><span class="mw-editsection-bracket">[</span><a href="/w/index.php?title=Bird_anatomy&action=edit&section=16" title="Edit section: Hind limb change"><span>edit</span></a><span class="mw-editsection-bracket">]</span></span></div> <p>A significant similarity in the structure of the hind limbs of birds and other <a href="/wiki/Dinosaur" title="Dinosaur">dinosaurs</a> is associated with their ability to walk on two legs, or <a href="/wiki/Bipedalism" title="Bipedalism">bipedalism</a>.<sup id="cite_ref-34" class="reference"><a href="#cite_note-34"><span class="cite-bracket">[</span>34<span class="cite-bracket">]</span></a></sup> In the 20th century, the prevailing opinion was that the transition to bipedalism occurred due to the transformation of the forelimbs into wings. Modern scientists believe that, on the contrary, it was a necessary condition for the occurrence of flight.<sup id="cite_ref-35" class="reference"><a href="#cite_note-35"><span class="cite-bracket">[</span>35<span class="cite-bracket">]</span></a></sup> </p> <figure typeof="mw:File/Thumb"><a href="/wiki/File:Harpagornis_claw_vs_eagle.png" class="mw-file-description"><img src="//upload.wikimedia.org/wikipedia/commons/thumb/f/f1/Harpagornis_claw_vs_eagle.png/300px-Harpagornis_claw_vs_eagle.png" decoding="async" width="300" height="235" class="mw-file-element" srcset="//upload.wikimedia.org/wikipedia/commons/thumb/f/f1/Harpagornis_claw_vs_eagle.png/450px-Harpagornis_claw_vs_eagle.png 1.5x, //upload.wikimedia.org/wikipedia/commons/thumb/f/f1/Harpagornis_claw_vs_eagle.png/600px-Harpagornis_claw_vs_eagle.png 2x" data-file-width="1430" data-file-height="1118" /></a><figcaption>Comparative morphology of the paw skeleton of the extinct <a href="/wiki/Haast%27s_eagle" title="Haast's eagle">Haast's eagle</a> with its <a href="/wiki/Common_descent" title="Common descent">closest living relative</a> the <a href="/wiki/Little_eagle" title="Little eagle">little eagle</a>.</figcaption></figure> <p>The transition to the use of only the hind limbs for movement was accompanied by an increase in the rigidity of the lumbar and sacral regions. The pubic bones of birds and some other bipedal dinosaurs are turned backward. Scientists associate this with a shift in the center of gravity of the body backward. The reason for this shift is called the transition to <a href="/wiki/Bipedality" class="mw-redirect" title="Bipedality">bipedality</a> or the development of powerful forelimbs, as in <a href="/wiki/Archaeopteryx" title="Archaeopteryx">Archaeopteryx</a>.<sup id="cite_ref-ReferenceA_36-0" class="reference"><a href="#cite_note-ReferenceA-36"><span class="cite-bracket">[</span>36<span class="cite-bracket">]</span></a></sup><sup id="cite_ref-Physical_theory,_origin_of_flight_37-0" class="reference"><a href="#cite_note-Physical_theory,_origin_of_flight-37"><span class="cite-bracket">[</span>37<span class="cite-bracket">]</span></a></sup> The large and heavy tail of two-legged dinosaurs may have been an additional support. Partial tail reduction and subsequent formation of <a href="/wiki/Pygostyle" title="Pygostyle">pygostyle</a> occurred due to the backward deviation of the first toe of the hind limb; in dinosaurs with a long rigid tail, the development of the foot proceeded differently. This process, apparently, took place in parallel in birds and some other dinosaurs. In general, the anisodactyl foot, which also has a better grasping ability and allows confident movement both on the ground and along branches, is ancestral for birds. Against this background, pterosaurs stand out, which, in the process of unsuccessful evolutionary changes, could not fully move on two legs, but instead developed a physical means of flight<sup class="noprint Inline-Template" style="white-space:nowrap;">[<i><a href="/wiki/Wikipedia:Please_clarify" title="Wikipedia:Please clarify"><span title="The text near this tag needs further explanation. (April 2021)">further explanation needed</span></a></i>]</sup> that was fundamentally different from birds.<sup id="cite_ref-Physical_theory,_origin_of_flight_37-1" class="reference"><a href="#cite_note-Physical_theory,_origin_of_flight-37"><span class="cite-bracket">[</span>37<span class="cite-bracket">]</span></a></sup> </p> <div class="mw-heading mw-heading4"><h4 id="Forelimb_changes">Forelimb changes</h4><span class="mw-editsection"><span class="mw-editsection-bracket">[</span><a href="/w/index.php?title=Bird_anatomy&action=edit&section=17" title="Edit section: Forelimb changes"><span>edit</span></a><span class="mw-editsection-bracket">]</span></span></div> <p>Changes in the hindlimbs did not affect the location of the forelimbs, which in birds remained laterally spaced, and in non-avian <a href="/wiki/Dinosaurs" class="mw-redirect" title="Dinosaurs">dinosaurs</a> they switched to a parasagittal orientation.<sup id="cite_ref-ReferenceA_36-1" class="reference"><a href="#cite_note-ReferenceA-36"><span class="cite-bracket">[</span>36<span class="cite-bracket">]</span></a></sup> At the same time, the forelimbs, freed from the support function, had ample opportunities for evolutionary changes. Proponents of the running hypothesis believe that <a href="/wiki/Flight" title="Flight">flight</a> was formed through fast running, bouncing, and then gliding. The forelimbs could be used for grasping after a jump or as "insect trapping nets", animals could wave them, helping themselves during the jump. According to the arboreal hypothesis, the ancestors of birds climbed trees with the help of their forelimbs, and from there they planned, after which they proceeded to flight.<sup id="cite_ref-38" class="reference"><a href="#cite_note-38"><span class="cite-bracket">[</span>38<span class="cite-bracket">]</span></a></sup> </p> <div class="mw-heading mw-heading2"><h2 id="Muscular_system">Muscular system</h2><span class="mw-editsection"><span class="mw-editsection-bracket">[</span><a href="/w/index.php?title=Bird_anatomy&action=edit&section=18" title="Edit section: Muscular system"><span>edit</span></a><span class="mw-editsection-bracket">]</span></span></div> <figure class="mw-default-size" typeof="mw:File/Thumb"><a href="/wiki/File:Wing_Muscles,_color.svg" class="mw-file-description"><img src="//upload.wikimedia.org/wikipedia/commons/thumb/0/02/Wing_Muscles%2C_color.svg/220px-Wing_Muscles%2C_color.svg.png" decoding="async" width="220" height="119" class="mw-file-element" srcset="//upload.wikimedia.org/wikipedia/commons/thumb/0/02/Wing_Muscles%2C_color.svg/330px-Wing_Muscles%2C_color.svg.png 1.5x, //upload.wikimedia.org/wikipedia/commons/thumb/0/02/Wing_Muscles%2C_color.svg/440px-Wing_Muscles%2C_color.svg.png 2x" data-file-width="912" data-file-height="493" /></a><figcaption>The supracoracoideus works using a pulley-like system to lift the wing while the pectorals provide the powerful downstroke</figcaption></figure> <p>Most birds have approximately 175 different muscles, mainly controlling the wings, skin, and legs. Overall, the muscle mass of birds is concentrated ventrally. The largest muscles in the bird are the pectorals, or the pectoralis major, which control the wings and make up about 15–25% of a flighted bird's body weight. They provide the powerful wing stroke essential for flight. The muscle deep to (underneath) the pectorals is the supracoracoideus, or the pectoralis minor. It raises the wing between wingbeats. Both muscle groups attach to the keel of the sternum. This is remarkable, because other vertebrates have the muscles to raise the upper limbs generally attached to areas on the back of the spine. The supracoracoideus and the pectorals together make up about 25–40% of the bird's full body weight.<sup id="cite_ref-:6_39-0" class="reference"><a href="#cite_note-:6-39"><span class="cite-bracket">[</span>39<span class="cite-bracket">]</span></a></sup> Caudal to the pectorals and supracoracoideus are the internal and external obliques which compress the abdomen. Additionally, there are other abdominal muscles present that expand and contract the chest, and hold the ribcage. The muscles of the wing, as seen in the labelled images, function mainly in extending or flexing the elbow, moving the wing as a whole or in extending or flexing particular digits. These muscles work to adjust the wings for flight and all other actions.<sup id="cite_ref-:6_39-1" class="reference"><a href="#cite_note-:6-39"><span class="cite-bracket">[</span>39<span class="cite-bracket">]</span></a></sup> Muscle composition does vary between species and even within families.<sup id="cite_ref-40" class="reference"><a href="#cite_note-40"><span class="cite-bracket">[</span>40<span class="cite-bracket">]</span></a></sup> </p> <figure class="mw-default-size" typeof="mw:File/Thumb"><a href="/wiki/File:Pigeon_wing_musculature,_ventral.png" class="mw-file-description"><img src="//upload.wikimedia.org/wikipedia/commons/thumb/8/8b/Pigeon_wing_musculature%2C_ventral.png/220px-Pigeon_wing_musculature%2C_ventral.png" decoding="async" width="220" height="119" class="mw-file-element" srcset="//upload.wikimedia.org/wikipedia/commons/thumb/8/8b/Pigeon_wing_musculature%2C_ventral.png/330px-Pigeon_wing_musculature%2C_ventral.png 1.5x, //upload.wikimedia.org/wikipedia/commons/thumb/8/8b/Pigeon_wing_musculature%2C_ventral.png/440px-Pigeon_wing_musculature%2C_ventral.png 2x" data-file-width="1009" data-file-height="544" /></a><figcaption>Labelled ventral musculature of a pigeon wing</figcaption></figure> <p>Birds have unique necks which are elongated with complex musculature as it must allow for the head to perform functions other animals may utilize pectoral limbs for.<sup id="cite_ref-:6_39-2" class="reference"><a href="#cite_note-:6-39"><span class="cite-bracket">[</span>39<span class="cite-bracket">]</span></a></sup> </p> <figure class="mw-default-size" typeof="mw:File/Thumb"><a href="/wiki/File:Dorsal_Wing_View.png" class="mw-file-description"><img src="//upload.wikimedia.org/wikipedia/commons/thumb/3/33/Dorsal_Wing_View.png/220px-Dorsal_Wing_View.png" decoding="async" width="220" height="120" class="mw-file-element" srcset="//upload.wikimedia.org/wikipedia/commons/thumb/3/33/Dorsal_Wing_View.png/330px-Dorsal_Wing_View.png 1.5x, //upload.wikimedia.org/wikipedia/commons/thumb/3/33/Dorsal_Wing_View.png/440px-Dorsal_Wing_View.png 2x" data-file-width="977" data-file-height="531" /></a><figcaption>Labelled dorsal musculature of a pigeon wing</figcaption></figure> <p>The skin muscles help a bird in its flight by adjusting the feathers, which are attached to the skin muscle and help the bird in its flight maneuvers as well as aiding in mating rituals. </p><p>There are only a few muscles in the trunk and the tail, but they are very strong and are essential for the bird. These include the lateralis caudae and the levator caudae which control movement of the tail and the spreading of rectrices, giving the tail a larger surface area which helps keep the bird in the air as well as aiding in turning.<sup id="cite_ref-:6_39-3" class="reference"><a href="#cite_note-:6-39"><span class="cite-bracket">[</span>39<span class="cite-bracket">]</span></a></sup> </p><p>Muscle composition and adaptation differ by theories of muscle adaptation in whether evolution of flight came from flapping or gliding first.<sup id="cite_ref-41" class="reference"><a href="#cite_note-41"><span class="cite-bracket">[</span>41<span class="cite-bracket">]</span></a></sup> </p> <div class="mw-heading mw-heading2"><h2 id="Integumentary_system">Integumentary system</h2><span class="mw-editsection"><span class="mw-editsection-bracket">[</span><a href="/w/index.php?title=Bird_anatomy&action=edit&section=19" title="Edit section: Integumentary system"><span>edit</span></a><span class="mw-editsection-bracket">]</span></span></div> <link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1236090951"><div role="note" class="hatnote navigation-not-searchable">See also: <a href="/wiki/Comb_(anatomy)" title="Comb (anatomy)">Comb (anatomy)</a>, <a href="/wiki/Lore_(anatomy)" title="Lore (anatomy)">Lore (anatomy)</a>, <a href="/wiki/Gular_skin" title="Gular skin">Gular skin</a>, and <a href="/wiki/Brooding_patch" class="mw-redirect" title="Brooding patch">Brooding patch</a></div> <figure class="mw-default-size mw-halign-right" typeof="mw:File/Thumb"><a href="/wiki/File:Strau%C3%9Fenfu%C3%9F.jpg" class="mw-file-description"><img src="//upload.wikimedia.org/wikipedia/commons/thumb/f/f1/Strau%C3%9Fenfu%C3%9F.jpg/220px-Strau%C3%9Fenfu%C3%9F.jpg" decoding="async" width="220" height="165" class="mw-file-element" srcset="//upload.wikimedia.org/wikipedia/commons/thumb/f/f1/Strau%C3%9Fenfu%C3%9F.jpg/330px-Strau%C3%9Fenfu%C3%9F.jpg 1.5x, //upload.wikimedia.org/wikipedia/commons/thumb/f/f1/Strau%C3%9Fenfu%C3%9F.jpg/440px-Strau%C3%9Fenfu%C3%9F.jpg 2x" data-file-width="2048" data-file-height="1536" /></a><figcaption>Ostrich foot integument (podotheca)</figcaption></figure> <div class="mw-heading mw-heading3"><h3 id="Scales">Scales</h3><span class="mw-editsection"><span class="mw-editsection-bracket">[</span><a href="/w/index.php?title=Bird_anatomy&action=edit&section=20" title="Edit section: Scales"><span>edit</span></a><span class="mw-editsection-bracket">]</span></span></div> <p>The <a href="/wiki/Scale_(anatomy)" class="mw-redirect" title="Scale (anatomy)">scales</a> of birds are composed of keratin, like beaks, claws, and spurs. They are found mainly on the toes and tarsi (lower leg of birds), usually up to the tibio-tarsal joint, but may be found further up the legs in some birds. In many of the <a href="/wiki/Eagle" title="Eagle">eagles</a> and <a href="/wiki/Owls" class="mw-redirect" title="Owls">owls</a> the legs are feathered down to (but not including) their toes.<sup id="cite_ref-42" class="reference"><a href="#cite_note-42"><span class="cite-bracket">[</span>42<span class="cite-bracket">]</span></a></sup><sup id="cite_ref-43" class="reference"><a href="#cite_note-43"><span class="cite-bracket">[</span>43<span class="cite-bracket">]</span></a></sup><sup id="cite_ref-44" class="reference"><a href="#cite_note-44"><span class="cite-bracket">[</span>44<span class="cite-bracket">]</span></a></sup> Most bird scales do not overlap significantly, except in the cases of <a href="/wiki/Kingfisher" title="Kingfisher">kingfishers</a> and <a href="/wiki/Woodpecker" title="Woodpecker">woodpeckers</a>. The scales and scutes of birds were originally thought to be <a href="/wiki/Homology_(biology)" title="Homology (biology)">homologous</a> to those of reptiles;<sup id="cite_ref-Lucas_45-0" class="reference"><a href="#cite_note-Lucas-45"><span class="cite-bracket">[</span>45<span class="cite-bracket">]</span></a></sup> however, more recent research suggests that scales in birds re-evolved after the evolution of feathers.<sup id="cite_ref-Sawyer_46-0" class="reference"><a href="#cite_note-Sawyer-46"><span class="cite-bracket">[</span>46<span class="cite-bracket">]</span></a></sup><sup id="cite_ref-Dhouailly_47-0" class="reference"><a href="#cite_note-Dhouailly-47"><span class="cite-bracket">[</span>47<span class="cite-bracket">]</span></a></sup><sup id="cite_ref-48" class="reference"><a href="#cite_note-48"><span class="cite-bracket">[</span>48<span class="cite-bracket">]</span></a></sup> </p><p>Bird embryos begin development with smooth skin. On the feet, the <a href="/wiki/Stratum_corneum" title="Stratum corneum">corneum</a>, or outermost layer, of this skin may keratinize, thicken and form scales. These scales can be organized into; </p> <ul><li>Cancella – minute scales which are really just a thickening and hardening of the skin, crisscrossed with shallow grooves.</li> <li>Scutella – scales that are not quite as large as scutes, such as those found on the <a href="/wiki/Caudal_(anatomical_term)" class="mw-redirect" title="Caudal (anatomical term)">caudal</a>, or hind part, of the chicken <a href="/wiki/Metatarsus" class="mw-redirect" title="Metatarsus">metatarsus</a>.</li> <li><a href="/wiki/Scute" title="Scute">Scutes</a> – the largest scales, usually on the <a href="/wiki/Anterior" class="mw-redirect" title="Anterior">anterior</a> surface of the metatarsus and <a href="/wiki/Dorsum_(biology)" class="mw-redirect" title="Dorsum (biology)">dorsal</a> surface of the toes.</li></ul> <p>The rows of scutes on the anterior of the metatarsus can be called an "acrometatarsium" or "acrotarsium". </p><p>Reticula are located on the <a href="/wiki/Anatomical_terms_of_location" title="Anatomical terms of location">lateral and medial</a> surfaces (sides) of the foot and were originally thought to be separate scales. However, histological and <a href="/wiki/Evolutionary_developmental_biology" title="Evolutionary developmental biology">evolutionary developmental</a> work in this area revealed that these structures lack beta-keratin (a hallmark of reptilian scales) and are entirely composed of alpha-keratin.<sup id="cite_ref-Dhouailly_47-1" class="reference"><a href="#cite_note-Dhouailly-47"><span class="cite-bracket">[</span>47<span class="cite-bracket">]</span></a></sup><sup id="cite_ref-stettenheim_49-0" class="reference"><a href="#cite_note-stettenheim-49"><span class="cite-bracket">[</span>49<span class="cite-bracket">]</span></a></sup> This, along with their unique structure, has led to the suggestion that these are actually feather buds that were arrested early in development.<sup id="cite_ref-Dhouailly_47-2" class="reference"><a href="#cite_note-Dhouailly-47"><span class="cite-bracket">[</span>47<span class="cite-bracket">]</span></a></sup> </p><p>Collectively, the scaly covering present on the foot of the birds is called podotheca. </p> <div class="mw-heading mw-heading3"><h3 id="Herbst_corpuscles_and_lore">Herbst corpuscles and lore</h3><span class="mw-editsection"><span class="mw-editsection-bracket">[</span><a href="/w/index.php?title=Bird_anatomy&action=edit&section=21" title="Edit section: Herbst corpuscles and lore"><span>edit</span></a><span class="mw-editsection-bracket">]</span></span></div> <p>The bills of many waders have <a href="/wiki/Herbst_corpuscle" class="mw-redirect" title="Herbst corpuscle">Herbst corpuscles</a> which help them find prey hidden under wet sand, by detecting minute pressure differences in the water.<sup id="cite_ref-50" class="reference"><a href="#cite_note-50"><span class="cite-bracket">[</span>50<span class="cite-bracket">]</span></a></sup> All extant birds can move the parts of the upper jaw relative to the brain case. However, this is more prominent in some birds and can be readily detected in parrots.<sup id="cite_ref-51" class="reference"><a href="#cite_note-51"><span class="cite-bracket">[</span>51<span class="cite-bracket">]</span></a></sup> </p><p>The region between the eye and bill on the side of a bird's head is called the <a href="/wiki/Lore_(anatomy)" title="Lore (anatomy)">lore</a>. This region is sometimes featherless, and the skin may be tinted, as in many species of the <a href="/wiki/Cormorant" title="Cormorant">cormorant</a> family. </p> <div class="mw-heading mw-heading3"><h3 id="Beak">Beak</h3><span class="mw-editsection"><span class="mw-editsection-bracket">[</span><a href="/w/index.php?title=Bird_anatomy&action=edit&section=22" title="Edit section: Beak"><span>edit</span></a><span class="mw-editsection-bracket">]</span></span></div> <link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1236090951"><div role="note" class="hatnote navigation-not-searchable">Main article: <a href="/wiki/Beak" title="Beak">Beak</a></div> <p>The beak, bill, or <a href="/wiki/Rostrum_(anatomy)" title="Rostrum (anatomy)">rostrum</a> is an external anatomical structure of birds which is used for eating and for <a href="/wiki/Preening_(bird)" class="mw-redirect" title="Preening (bird)">preening</a>, manipulating objects, killing prey, fighting, probing for food, <a href="/wiki/Courtship_in_animals" class="mw-redirect" title="Courtship in animals">courtship</a> and feeding young. Although beaks vary significantly in size, shape and color, they share a similar underlying structure. Two bony projections—the upper and lower mandibles—covered with a thin keratinized layer of epidermis known as the <a href="/wiki/Beak#Rhamphotheca" title="Beak">rhamphotheca</a>. In most species, two holes known as nares lead to the respiratory system. </p> <div class="mw-heading mw-heading2"><h2 id="Respiratory_system">Respiratory system</h2><span class="mw-editsection"><span class="mw-editsection-bracket">[</span><a href="/w/index.php?title=Bird_anatomy&action=edit&section=23" title="Edit section: Respiratory system"><span>edit</span></a><span class="mw-editsection-bracket">]</span></span></div> <link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1236090951"><div role="note" class="hatnote navigation-not-searchable">See also: <a href="/wiki/Respiratory_system#Birds" title="Respiratory system">Respiratory system § Birds</a></div> <figure class="mw-halign-left" typeof="mw:File/Thumb"><a href="/wiki/File:Cranial_sinus_and_postcranial_air_sac_systems_in_birds.svg" class="mw-file-description"><img src="//upload.wikimedia.org/wikipedia/commons/thumb/1/19/Cranial_sinus_and_postcranial_air_sac_systems_in_birds.svg/250px-Cranial_sinus_and_postcranial_air_sac_systems_in_birds.svg.png" decoding="async" width="250" height="198" class="mw-file-element" srcset="//upload.wikimedia.org/wikipedia/commons/thumb/1/19/Cranial_sinus_and_postcranial_air_sac_systems_in_birds.svg/375px-Cranial_sinus_and_postcranial_air_sac_systems_in_birds.svg.png 1.5x, //upload.wikimedia.org/wikipedia/commons/thumb/1/19/Cranial_sinus_and_postcranial_air_sac_systems_in_birds.svg/500px-Cranial_sinus_and_postcranial_air_sac_systems_in_birds.svg.png 2x" data-file-width="683" data-file-height="541" /></a><figcaption>The arrangement of the air sacs and lungs in birds</figcaption></figure> <figure class="mw-halign-right" typeof="mw:File/Thumb"><a href="/wiki/File:Bird%27s_respiratory_system.jpg" class="mw-file-description"><img src="//upload.wikimedia.org/wikipedia/commons/thumb/4/43/Bird%27s_respiratory_system.jpg/250px-Bird%27s_respiratory_system.jpg" decoding="async" width="250" height="176" class="mw-file-element" srcset="//upload.wikimedia.org/wikipedia/commons/thumb/4/43/Bird%27s_respiratory_system.jpg/375px-Bird%27s_respiratory_system.jpg 1.5x, //upload.wikimedia.org/wikipedia/commons/thumb/4/43/Bird%27s_respiratory_system.jpg/500px-Bird%27s_respiratory_system.jpg 2x" data-file-width="2000" data-file-height="1408" /></a><figcaption>The anatomy of bird's respiratory system, showing the relationships of the trachea, primary and intra-pulmonary bronchi, the dorso- and ventro-bronchi, with the parabronchi running between the two. The posterior and anterior air sacs are also indicated, but not to scale.</figcaption></figure> <figure class="mw-halign-right" typeof="mw:File/Thumb"><a href="/wiki/File:BirdRespiration.svg" class="mw-file-description"><img src="//upload.wikimedia.org/wikipedia/commons/thumb/f/f2/BirdRespiration.svg/250px-BirdRespiration.svg.png" decoding="async" width="250" height="303" class="mw-file-element" srcset="//upload.wikimedia.org/wikipedia/commons/thumb/f/f2/BirdRespiration.svg/375px-BirdRespiration.svg.png 1.5x, //upload.wikimedia.org/wikipedia/commons/thumb/f/f2/BirdRespiration.svg/500px-BirdRespiration.svg.png 2x" data-file-width="2803" data-file-height="3395" /></a><figcaption>Inhalation–exhalation cycle in birds.</figcaption></figure> <p>Due to the high <a href="/wiki/Metabolic_rate" class="mw-redirect" title="Metabolic rate">metabolic rate</a> required for flight, birds have a high oxygen demand. Their highly effective <a href="/wiki/Respiratory_system" title="Respiratory system">respiratory system</a> helps them meet that demand. </p><p>Although birds have lungs, theirs are fairly rigid structures that do not expand and contract as they do in mammals, reptiles and many amphibians. Instead, the structures that act as the bellows that <a href="/wiki/Ventilation_(physiology)" class="mw-redirect" title="Ventilation (physiology)">ventilate</a> the lungs are the <a href="/wiki/Air_sacs" class="mw-redirect" title="Air sacs">air sacs</a>, which are distributed throughout much of the birds' bodies.<sup id="cite_ref-52" class="reference"><a href="#cite_note-52"><span class="cite-bracket">[</span>52<span class="cite-bracket">]</span></a></sup> The air sacs move air unidirectionally through the <b>parabronchi</b> of the rigid lungs.<sup id="cite_ref-Maina2005_53-0" class="reference"><a href="#cite_note-Maina2005-53"><span class="cite-bracket">[</span>53<span class="cite-bracket">]</span></a></sup><sup id="cite_ref-Krautwald-Junghanns,_et_al._2010_54-0" class="reference"><a href="#cite_note-Krautwald-Junghanns,_et_al._2010-54"><span class="cite-bracket">[</span>54<span class="cite-bracket">]</span></a></sup> The primary mechanism of unidirectional flows in bird lungs is flow irreversibility at high <a href="/wiki/Reynolds_number" title="Reynolds number">Reynolds number</a> manifested in asymmetric junctions and their loop-forming connectivity.<sup id="cite_ref-55" class="reference"><a href="#cite_note-55"><span class="cite-bracket">[</span>55<span class="cite-bracket">]</span></a></sup> </p><p>Although avian lungs are smaller than those of mammals of comparable size, the air sacs account for 15% of the total body volume, whereas in mammals, the <a href="/wiki/Pulmonary_alveolus" title="Pulmonary alveolus">alveoli</a>, which act as the bellows, constitute only 7% of the total body volume.<sup id="cite_ref-Whittow_2000_233–241_56-0" class="reference"><a href="#cite_note-Whittow_2000_233–241-56"><span class="cite-bracket">[</span>56<span class="cite-bracket">]</span></a></sup> Overall, avian lungs have a respiratory surface area that is approximately 15% greater, a pulmonary capillary blood volume that is 2.5-3 larger and a blood-gas barrier that is 56-67% thinner than those in the lungs of mammals of a similar body mass.<sup id="cite_ref-57" class="reference"><a href="#cite_note-57"><span class="cite-bracket">[</span>57<span class="cite-bracket">]</span></a></sup><sup id="cite_ref-58" class="reference"><a href="#cite_note-58"><span class="cite-bracket">[</span>58<span class="cite-bracket">]</span></a></sup> The walls of the air sacs do not have a good blood supply and so do not play a direct role in <a href="/wiki/Gas_exchange" title="Gas exchange">gas exchange</a>. </p><p>Birds lack a <a href="/wiki/Thoracic_diaphragm" title="Thoracic diaphragm">diaphragm</a>, and therefore use their <a href="/wiki/Intercostal_muscle" class="mw-redirect" title="Intercostal muscle">intercostal</a> and <a href="/wiki/Abdominal_muscles" title="Abdominal muscles">abdominal muscles</a> to expand and contract their entire thoraco-abdominal cavities, thus rhythmically changing the volumes of all their air sacs in unison (illustration on the right). The active phase of respiration in birds is exhalation, requiring contraction of their muscles of respiration.<sup id="cite_ref-Krautwald-Junghanns,_et_al._2010_54-1" class="reference"><a href="#cite_note-Krautwald-Junghanns,_et_al._2010-54"><span class="cite-bracket">[</span>54<span class="cite-bracket">]</span></a></sup> Relaxation of these muscles causes inhalation. </p><p>Three distinct sets of organs perform respiration — the <a href="/wiki/Anatomical_terms_of_location#Anterior_and_posterior" title="Anatomical terms of location">anterior</a> air sacs (interclavicular, cervicals, and anterior thoracics), the <a href="/wiki/Lung" title="Lung">lungs</a>, and the <a href="/wiki/Anatomical_terms_of_location#Anterior_and_posterior" title="Anatomical terms of location">posterior</a> air sacs (posterior thoracics and abdominals). Typically there are nine air sacs within the system;<sup id="cite_ref-Krautwald-Junghanns,_et_al._2010_54-2" class="reference"><a href="#cite_note-Krautwald-Junghanns,_et_al._2010-54"><span class="cite-bracket">[</span>54<span class="cite-bracket">]</span></a></sup> however, that number can range between seven and twelve, depending on the species of bird. <a href="/wiki/Passerine" title="Passerine">Passerines</a> possess seven air sacs, as the clavicular air sacs may interconnect or be fused with the anterior thoracic sacs. </p><p>During inhalation, environmental air initially enters the bird through the <a href="/wiki/Nostril" title="Nostril">nostrils</a> from where it is heated, humidified, and filtered in the nasal passages and upper parts of the trachea.<sup id="cite_ref-Whittow_2000_233–241_56-1" class="reference"><a href="#cite_note-Whittow_2000_233–241-56"><span class="cite-bracket">[</span>56<span class="cite-bracket">]</span></a></sup> From there, the air enters the lower <a href="/wiki/Vertebrate_trachea" class="mw-redirect" title="Vertebrate trachea">trachea</a> and continues to just beyond the <a href="/wiki/Syrinx_(bird_anatomy)" title="Syrinx (bird anatomy)">syrinx</a>, at which point the trachea branches into two <a href="/wiki/Bronchus" title="Bronchus">primary bronchi</a>, going to the two lungs. The primary bronchi enter the lungs to become the intrapulmonary bronchi, which give off a set of parallel branches called ventrobronchi and, a little further on, an equivalent set of dorsobronchi.<sup id="cite_ref-AvResp_59-0" class="reference"><a href="#cite_note-AvResp-59"><span class="cite-bracket">[</span>59<span class="cite-bracket">]</span></a></sup> The ends of the intrapulmonary bronchi discharge air into the posterior air sacs at the <a href="/wiki/Anatomical_terms_of_location#Caudal" title="Anatomical terms of location">caudal</a> end of the bird. Each pair of dorso-ventrobronchi is connected by a large number of parallel microscopic air capillaries (or parabronchi) where <a href="/wiki/Gas_exchange" title="Gas exchange">gas exchange</a> occurs.<sup id="cite_ref-AvResp_59-1" class="reference"><a href="#cite_note-AvResp-59"><span class="cite-bracket">[</span>59<span class="cite-bracket">]</span></a></sup> As the bird inhales, tracheal air flows through the intrapulmonary bronchi into the posterior air sacs, as well as into the <i>dorso</i>bronchi (but not into the ventrobronchi whose openings into the intrapulmonary bronchi were previously believed to be tightly closed during inhalation.<sup id="cite_ref-AvResp_59-2" class="reference"><a href="#cite_note-AvResp-59"><span class="cite-bracket">[</span>59<span class="cite-bracket">]</span></a></sup> However, more recent studies have shown that the aerodynamics of the bronchial architecture directs the inhaled air away from the openings of the ventrobronchi, into the continuation of the intrapulmonary bronchus towards the dorsobronchi and posterior air sacs<sup id="cite_ref-Maina2005_53-1" class="reference"><a href="#cite_note-Maina2005-53"><span class="cite-bracket">[</span>53<span class="cite-bracket">]</span></a></sup><sup id="cite_ref-sturkie_60-0" class="reference"><a href="#cite_note-sturkie-60"><span class="cite-bracket">[</span>60<span class="cite-bracket">]</span></a></sup>). From the dorsobronchi the air flows through the parabronchi (and therefore the gas exchanger) to the ventrobronchi from where the air can only escape into the expanding anterior air sacs. So, during inhalation, both the posterior and anterior air sacs expand,<sup id="cite_ref-AvResp_59-3" class="reference"><a href="#cite_note-AvResp-59"><span class="cite-bracket">[</span>59<span class="cite-bracket">]</span></a></sup> the posterior air sacs filling with fresh inhaled air, while the anterior air sacs fill with "spent" (oxygen-poor) air that has just passed through the lungs. </p><p>During exhalation the intrapulmonary bronchi were believed to be tightly constricted between the region where the ventrobronchi branch off and the region where the dorsobronchi branch off.<sup id="cite_ref-AvResp_59-4" class="reference"><a href="#cite_note-AvResp-59"><span class="cite-bracket">[</span>59<span class="cite-bracket">]</span></a></sup> But it is now believed that more intricate aerodynamic features have the same effect.<sup id="cite_ref-Maina2005_53-2" class="reference"><a href="#cite_note-Maina2005-53"><span class="cite-bracket">[</span>53<span class="cite-bracket">]</span></a></sup><sup id="cite_ref-sturkie_60-1" class="reference"><a href="#cite_note-sturkie-60"><span class="cite-bracket">[</span>60<span class="cite-bracket">]</span></a></sup> The contracting posterior air sacs can therefore only empty into the dorsobronchi. From there the fresh air from the posterior air sacs flows through the parabronchi (in the same direction as occurred during inhalation) into ventrobronchi. The air passages connecting the ventrobronchi and anterior air sacs to the intrapulmonary bronchi open up during exhalation, thus allowing oxygen-poor air from these two organs to escape via the trachea to the exterior.<sup id="cite_ref-AvResp_59-5" class="reference"><a href="#cite_note-AvResp-59"><span class="cite-bracket">[</span>59<span class="cite-bracket">]</span></a></sup> Oxygenated air therefore flows constantly (during the entire breathing cycle) in a single direction through the parabronchi.<sup id="cite_ref-ritchisong_1-1" class="reference"><a href="#cite_note-ritchisong-1"><span class="cite-bracket">[</span>1<span class="cite-bracket">]</span></a></sup> </p> <figure class="mw-halign-left" typeof="mw:File/Thumb"><a href="/wiki/File:Cross-current_exchanger.jpg" class="mw-file-description"><img src="//upload.wikimedia.org/wikipedia/commons/thumb/2/2d/Cross-current_exchanger.jpg/250px-Cross-current_exchanger.jpg" decoding="async" width="250" height="143" class="mw-file-element" srcset="//upload.wikimedia.org/wikipedia/commons/thumb/2/2d/Cross-current_exchanger.jpg/375px-Cross-current_exchanger.jpg 1.5x, //upload.wikimedia.org/wikipedia/commons/thumb/2/2d/Cross-current_exchanger.jpg/500px-Cross-current_exchanger.jpg 2x" data-file-width="4000" data-file-height="2288" /></a><figcaption>The <a href="/wiki/Countercurrent_exchange" title="Countercurrent exchange">cross-current</a> respiratory gas exchanger in the lungs of birds. Air is forced from the air sacs unidirectionally (from right to left in the diagram) through the parabronchi. The pulmonary capillaries surround the parabronchi in the manner shown (blood flowing from below the parabronchus to above it in the diagram).<sup id="cite_ref-AvResp_59-6" class="reference"><a href="#cite_note-AvResp-59"><span class="cite-bracket">[</span>59<span class="cite-bracket">]</span></a></sup><sup id="cite_ref-graham_61-0" class="reference"><a href="#cite_note-graham-61"><span class="cite-bracket">[</span>61<span class="cite-bracket">]</span></a></sup> Blood or air with a high oxygen content is shown in red; oxygen-poor air or blood is shown in various shades of purple-blue.</figcaption></figure><p>The blood flow through the bird lung is at right angles to the flow of air through the parabronchi, forming a cross-current flow exchange system (see illustration on the left).<sup id="cite_ref-AvResp_59-7" class="reference"><a href="#cite_note-AvResp-59"><span class="cite-bracket">[</span>59<span class="cite-bracket">]</span></a></sup><sup id="cite_ref-graham_61-1" class="reference"><a href="#cite_note-graham-61"><span class="cite-bracket">[</span>61<span class="cite-bracket">]</span></a></sup> The <a href="/wiki/Blood_gas_tension" title="Blood gas tension">partial pressure of oxygen</a> in the parabronchi declines along their lengths as O<sub>2</sub> diffuses into the blood. The blood capillaries leaving the exchanger near the entrance of airflow take up more O<sub>2</sub> than do the capillaries leaving near the exit end of the parabronchi. When the contents of all capillaries mix, the final partial pressure of oxygen of the mixed pulmonary venous blood is higher than that of the exhaled air,<sup id="cite_ref-AvResp_59-8" class="reference"><a href="#cite_note-AvResp-59"><span class="cite-bracket">[</span>59<span class="cite-bracket">]</span></a></sup><sup id="cite_ref-graham_61-2" class="reference"><a href="#cite_note-graham-61"><span class="cite-bracket">[</span>61<span class="cite-bracket">]</span></a></sup> but is nevertheless less than half that of the inhaled air,<sup id="cite_ref-AvResp_59-9" class="reference"><a href="#cite_note-AvResp-59"><span class="cite-bracket">[</span>59<span class="cite-bracket">]</span></a></sup> thus achieving roughly the same systemic arterial blood partial pressure of oxygen as <a href="/wiki/Respiratory_system#Gas_exchange" title="Respiratory system">mammals do with their bellows-type lungs</a>.<sup id="cite_ref-AvResp_59-10" class="reference"><a href="#cite_note-AvResp-59"><span class="cite-bracket">[</span>59<span class="cite-bracket">]</span></a></sup> </p><p>The trachea is an area of <a href="/wiki/Dead_space_(physiology)" title="Dead space (physiology)">dead space</a>: the oxygen-poor air it contains at the end of exhalation is the first air to re-enter the posterior air sacs and lungs. In comparison to the <a href="/wiki/Respiratory_system#Anatomy" title="Respiratory system">mammalian respiratory tract</a>, the dead space volume in a bird is, on average, 4.5 times greater than it is in mammals of the same size.<sup id="cite_ref-AvResp_59-11" class="reference"><a href="#cite_note-AvResp-59"><span class="cite-bracket">[</span>59<span class="cite-bracket">]</span></a></sup><sup id="cite_ref-Whittow_2000_233–241_56-2" class="reference"><a href="#cite_note-Whittow_2000_233–241-56"><span class="cite-bracket">[</span>56<span class="cite-bracket">]</span></a></sup> Birds with long necks will inevitably have long tracheae, and must therefore take deeper breaths than mammals do to make allowances for their greater dead space volumes. In some birds (e.g. the <a href="/wiki/Whooper_swan" title="Whooper swan">whooper swan</a>, <i>Cygnus cygnus</i>, the <a href="/wiki/White_spoonbill" class="mw-redirect" title="White spoonbill">white spoonbill</a>, <i>Platalea leucorodia</i>, the <a href="/wiki/Whooping_crane" title="Whooping crane">whooping crane</a>, <i>Grus americana</i>, and the <a href="/wiki/Helmeted_curassow" title="Helmeted curassow">helmeted curassow</a>, <i>Pauxi pauxi</i>) the trachea, which some cranes can be 1.5 m long,<sup id="cite_ref-AvResp_59-12" class="reference"><a href="#cite_note-AvResp-59"><span class="cite-bracket">[</span>59<span class="cite-bracket">]</span></a></sup> is coiled back and forth within the body, drastically increasing the dead space ventilation.<sup id="cite_ref-AvResp_59-13" class="reference"><a href="#cite_note-AvResp-59"><span class="cite-bracket">[</span>59<span class="cite-bracket">]</span></a></sup> The purpose of this extraordinary feature is unknown. </p><p>Air passes unidirectionally through the lungs during both exhalation and inspiration, causing, except for the oxygen-poor dead space air left in the trachea after exhalation and breathed in at the beginning of inhalation, little to no mixing of new oxygen-rich air with spent oxygen-poor air (as occurs in <a href="/wiki/Respiratory_system#Gas_exchange" title="Respiratory system">mammalian lungs</a>), changing only (from oxygen-rich to oxygen-poor) as it moves (unidirectionally) through the parabronchi. </p><p> Avian lungs do not have <a href="/wiki/Pulmonary_alveolus" title="Pulmonary alveolus">alveoli</a> as mammalian lungs do. Instead they contain millions of narrow passages known as parabronchi, connecting the dorsobronchi to the ventrobronchi at either ends of the lungs. Air flows anteriorly (caudal to cranial) through the parallel parabronchi. These parabronchi have honeycombed walls. The cells of the honeycomb are dead-end air vesicles, called <i>atria</i>, which project <a href="/wiki/Anatomical_terms_of_location" title="Anatomical terms of location">radially</a> from the parabronchi. The <i>atria</i> are the site of <a href="/wiki/Gas_exchange" title="Gas exchange">gas exchange</a> by simple diffusion.<sup id="cite_ref-62" class="reference"><a href="#cite_note-62"><span class="cite-bracket">[</span>62<span class="cite-bracket">]</span></a></sup> The blood flow around the parabronchi (and their atria), forms a cross-current gas exchanger (see diagram on the left).<sup id="cite_ref-AvResp_59-14" class="reference"><a href="#cite_note-AvResp-59"><span class="cite-bracket">[</span>59<span class="cite-bracket">]</span></a></sup><sup id="cite_ref-graham_61-3" class="reference"><a href="#cite_note-graham-61"><span class="cite-bracket">[</span>61<span class="cite-bracket">]</span></a></sup></p><figure class="mw-default-size mw-halign-right" typeof="mw:File/Thumb"><a href="/wiki/File:Human_Heart_vs_Chicken_Heart.png" class="mw-file-description"><img src="//upload.wikimedia.org/wikipedia/commons/thumb/0/0f/Human_Heart_vs_Chicken_Heart.png/220px-Human_Heart_vs_Chicken_Heart.png" decoding="async" width="220" height="116" class="mw-file-element" srcset="//upload.wikimedia.org/wikipedia/commons/thumb/0/0f/Human_Heart_vs_Chicken_Heart.png/330px-Human_Heart_vs_Chicken_Heart.png 1.5x, //upload.wikimedia.org/wikipedia/commons/thumb/0/0f/Human_Heart_vs_Chicken_Heart.png/440px-Human_Heart_vs_Chicken_Heart.png 2x" data-file-width="954" data-file-height="503" /></a><figcaption>The human heart (left) and chicken heart (right) share many similar characteristics. Avian hearts pump faster than mammalian hearts. Due to the faster heart rate, the muscles surrounding the ventricles of the chicken heart are thicker. Both hearts are labeled with the following parts: 1. Ascending <a href="/wiki/Aorta" title="Aorta">Aorta</a> 2. Left <a href="/wiki/Atrium_(heart)" title="Atrium (heart)">Atrium</a> 3. Left <a href="/wiki/Ventricle_(heart)" title="Ventricle (heart)">Ventricle</a> 4. Right Ventricle 5. Right Atrium. In chickens and others birds, the <a href="/wiki/Superior_vena_cava" title="Superior vena cava">superior cava</a> is double.</figcaption></figure> <p>All species of birds with the exception of the penguin, have a small region of their lungs devoted to "neopulmonic parabronchi". This unorganized network of microscopic tubes branches off from the posterior air sacs, and open haphazardly into both the dorso- and ventrobronchi, as well as directly into the intrapulmonary bronchi. Unlike the parabronchi, in which the air moves unidirectionally, the air flow in the neopulmonic parabronchi is bidirectional. The neopulmonic parabronchi never make up more than 25% of the total gas exchange surface of birds.<sup id="cite_ref-Whittow_2000_233–241_56-3" class="reference"><a href="#cite_note-Whittow_2000_233–241-56"><span class="cite-bracket">[</span>56<span class="cite-bracket">]</span></a></sup> </p> <figure class="mw-default-size" typeof="mw:File/Thumb"><a href="/wiki/File:Stebbins_Guide_to_Birds_022_outline.jpg" class="mw-file-description"><img src="//upload.wikimedia.org/wikipedia/commons/thumb/f/ff/Stebbins_Guide_to_Birds_022_outline.jpg/220px-Stebbins_Guide_to_Birds_022_outline.jpg" decoding="async" width="220" height="124" class="mw-file-element" srcset="//upload.wikimedia.org/wikipedia/commons/thumb/f/ff/Stebbins_Guide_to_Birds_022_outline.jpg/330px-Stebbins_Guide_to_Birds_022_outline.jpg 1.5x, //upload.wikimedia.org/wikipedia/commons/thumb/f/ff/Stebbins_Guide_to_Birds_022_outline.jpg/440px-Stebbins_Guide_to_Birds_022_outline.jpg 2x" data-file-width="1280" data-file-height="720" /></a><figcaption>Vocal Bird anatomy: Birds produce sounds through the air that passes through the Syrinx, which is shown close up in the bottom right.</figcaption></figure> <p>In order for birds to produce sound, they use an organ located above the lungs called the <a href="/wiki/Syrinx_(bird_anatomy)" title="Syrinx (bird anatomy)">syrinx</a>, which is composed of tracheal rings, syringeal muscles, Tympaniform membrane, and internal bony structures that contribute to the production of sound. Air then passes through this organ, resulting in the vocalization of birds. Sound can then be produced through the movement of the Tympaniform membrane. Pitch can also be changed by opening and closing of the Tympaniform membrane, allowing for higher and lower production of sound.<sup id="cite_ref-63" class="reference"><a href="#cite_note-63"><span class="cite-bracket">[</span>63<span class="cite-bracket">]</span></a></sup> </p> <link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1236090951"><div role="note" class="hatnote navigation-not-searchable">See also: <a href="/wiki/Syrinx_(bird_anatomy)" title="Syrinx (bird anatomy)">Syrinx (bird anatomy)</a></div> <div class="mw-heading mw-heading2"><h2 id="Circulatory_system">Circulatory system</h2><span class="mw-editsection"><span class="mw-editsection-bracket">[</span><a href="/w/index.php?title=Bird_anatomy&action=edit&section=24" title="Edit section: Circulatory system"><span>edit</span></a><span class="mw-editsection-bracket">]</span></span></div> <p>Birds have a four-chambered <a href="/wiki/Heart" title="Heart">heart</a>,<sup id="cite_ref-64" class="reference"><a href="#cite_note-64"><span class="cite-bracket">[</span>64<span class="cite-bracket">]</span></a></sup> in common with mammals, and some reptiles (mainly the <a href="/wiki/Crocodilia" title="Crocodilia">crocodilia</a>). This adaptation allows for an efficient nutrient and oxygen transport throughout the body, providing birds with energy to fly and maintain high levels of activity. A <a href="/wiki/Ruby-throated_hummingbird" title="Ruby-throated hummingbird">ruby-throated hummingbird</a>'s heart beats up to 1200 times per minute (about 20 beats per second).<sup id="cite_ref-65" class="reference"><a href="#cite_note-65"><span class="cite-bracket">[</span>65<span class="cite-bracket">]</span></a></sup> </p> <div class="mw-heading mw-heading2"><h2 id="Digestive_system">Digestive system</h2><span class="mw-editsection"><span class="mw-editsection-bracket">[</span><a href="/w/index.php?title=Bird_anatomy&action=edit&section=25" title="Edit section: Digestive system"><span>edit</span></a><span class="mw-editsection-bracket">]</span></span></div> <figure class="mw-default-size" typeof="mw:File/Thumb"><a href="/wiki/File:Dissected_Pigeon_Crop.png" class="mw-file-description"><img src="//upload.wikimedia.org/wikipedia/commons/thumb/5/53/Dissected_Pigeon_Crop.png/220px-Dissected_Pigeon_Crop.png" decoding="async" width="220" height="338" class="mw-file-element" srcset="//upload.wikimedia.org/wikipedia/commons/thumb/5/53/Dissected_Pigeon_Crop.png/330px-Dissected_Pigeon_Crop.png 1.5x, //upload.wikimedia.org/wikipedia/commons/thumb/5/53/Dissected_Pigeon_Crop.png/440px-Dissected_Pigeon_Crop.png 2x" data-file-width="583" data-file-height="896" /></a><figcaption>Pigeon crop containing ingested food particles is highlighted in yellow. The crop is an out-pouching of the esophagus and the wall of the esophagus is shown in blue.</figcaption></figure> <figure class="mw-default-size" typeof="mw:File/Thumb"><a href="/wiki/File:Anatomy_and_physiology_of_animals_Stomach_%26_small_intestine_of_hen.jpg" class="mw-file-description"><img src="//upload.wikimedia.org/wikipedia/commons/thumb/c/c2/Anatomy_and_physiology_of_animals_Stomach_%26_small_intestine_of_hen.jpg/220px-Anatomy_and_physiology_of_animals_Stomach_%26_small_intestine_of_hen.jpg" decoding="async" width="220" height="113" class="mw-file-element" srcset="//upload.wikimedia.org/wikipedia/commons/thumb/c/c2/Anatomy_and_physiology_of_animals_Stomach_%26_small_intestine_of_hen.jpg/330px-Anatomy_and_physiology_of_animals_Stomach_%26_small_intestine_of_hen.jpg 1.5x, //upload.wikimedia.org/wikipedia/commons/thumb/c/c2/Anatomy_and_physiology_of_animals_Stomach_%26_small_intestine_of_hen.jpg/440px-Anatomy_and_physiology_of_animals_Stomach_%26_small_intestine_of_hen.jpg 2x" data-file-width="604" data-file-height="310" /></a><figcaption>Simplified depiction of avian digestive system.</figcaption></figure> <div class="mw-heading mw-heading3"><h3 id="Crop">Crop</h3><span class="mw-editsection"><span class="mw-editsection-bracket">[</span><a href="/w/index.php?title=Bird_anatomy&action=edit&section=26" title="Edit section: Crop"><span>edit</span></a><span class="mw-editsection-bracket">]</span></span></div> <figure class="mw-default-size" typeof="mw:File/Thumb"><a href="/wiki/File:PigeonAnatomy.png" class="mw-file-description"><img src="//upload.wikimedia.org/wikipedia/commons/thumb/e/ea/PigeonAnatomy.png/220px-PigeonAnatomy.png" decoding="async" width="220" height="346" class="mw-file-element" srcset="//upload.wikimedia.org/wikipedia/commons/thumb/e/ea/PigeonAnatomy.png/330px-PigeonAnatomy.png 1.5x, //upload.wikimedia.org/wikipedia/commons/thumb/e/ea/PigeonAnatomy.png/440px-PigeonAnatomy.png 2x" data-file-width="684" data-file-height="1076" /></a><figcaption><a href="/wiki/Alimentary_canal" class="mw-redirect" title="Alimentary canal">Alimentary canal</a> of the bird exposed</figcaption></figure> <p>Many birds possess a muscular pouch along the <a href="/wiki/Esophagus" title="Esophagus">esophagus</a> called a <a href="/wiki/Crop_(anatomy)" title="Crop (anatomy)">crop</a>. The crop functions to both soften food and regulate its flow through the system by storing it temporarily. The size and shape of the crop is quite variable among the birds.<sup id="cite_ref-:4_66-0" class="reference"><a href="#cite_note-:4-66"><span class="cite-bracket">[</span>66<span class="cite-bracket">]</span></a></sup> Members of the family <a href="/wiki/Columbidae" title="Columbidae">Columbidae</a>, such as <a href="/wiki/Pigeons" class="mw-redirect" title="Pigeons">pigeons</a>, produce a nutritious <a href="/wiki/Crop_milk" title="Crop milk">crop milk</a> which is fed to their young by <a href="/wiki/Regurgitation_(digestion)" title="Regurgitation (digestion)">regurgitation</a>.<sup id="cite_ref-:5_67-0" class="reference"><a href="#cite_note-:5-67"><span class="cite-bracket">[</span>67<span class="cite-bracket">]</span></a></sup> </p> <div class="mw-heading mw-heading3"><h3 id="Proventriculus">Proventriculus</h3><span class="mw-editsection"><span class="mw-editsection-bracket">[</span><a href="/w/index.php?title=Bird_anatomy&action=edit&section=27" title="Edit section: Proventriculus"><span>edit</span></a><span class="mw-editsection-bracket">]</span></span></div> <p>The avian <a href="/wiki/Stomach" title="Stomach">stomach</a> is composed of two organs, the <a href="/wiki/Proventriculus" title="Proventriculus">proventriculus</a> and the <a href="/wiki/Gizzard" title="Gizzard">gizzard</a> that work together during <a href="/wiki/Digestion" title="Digestion">digestion</a>. The proventriculus is a rod shaped tube, which is found between the esophagus and the gizzard, that secretes <a href="/wiki/Hydrochloric_acid" title="Hydrochloric acid">hydrochloric acid</a> and <a href="/wiki/Pepsin#Precursor" title="Pepsin">pepsinogen</a> into the <a href="/wiki/Gastrointestinal_tract" title="Gastrointestinal tract">digestive tract</a>.<sup id="cite_ref-:5_67-1" class="reference"><a href="#cite_note-:5-67"><span class="cite-bracket">[</span>67<span class="cite-bracket">]</span></a></sup> The acid converts the inactive pepsinogen into the active <a href="/wiki/Protease" title="Protease">proteolytic enzyme</a>, <a href="/wiki/Pepsin" title="Pepsin">pepsin</a>, which breaks down specific <a href="/wiki/Peptide_bond" title="Peptide bond">peptide bonds</a> found in <a href="/wiki/Protein" title="Protein">proteins</a>, to produce a set of <a href="/wiki/Peptide" title="Peptide">peptides</a>, which are <a href="/wiki/Amino_acid#Proteinogenic_amino_acids" title="Amino acid">amino acid chains</a> that are shorter than the original dietary protein.<sup id="cite_ref-stryer_68-0" class="reference"><a href="#cite_note-stryer-68"><span class="cite-bracket">[</span>68<span class="cite-bracket">]</span></a></sup><sup id="cite_ref-69" class="reference"><a href="#cite_note-69"><span class="cite-bracket">[</span>69<span class="cite-bracket">]</span></a></sup> The <a href="/wiki/Gastric_acid" title="Gastric acid">gastric juices</a> (hydrochloric acid and pepsinogen) are mixed with the stomach contents through the muscular contractions of the gizzard.<sup id="cite_ref-70" class="reference"><a href="#cite_note-70"><span class="cite-bracket">[</span>70<span class="cite-bracket">]</span></a></sup> </p> <div class="mw-heading mw-heading3"><h3 id="Gizzard">Gizzard</h3><span class="mw-editsection"><span class="mw-editsection-bracket">[</span><a href="/w/index.php?title=Bird_anatomy&action=edit&section=28" title="Edit section: Gizzard"><span>edit</span></a><span class="mw-editsection-bracket">]</span></span></div> <p>The gizzard is composed of four muscular bands that rotate and crush food by shifting the food from one area to the next within the gizzard. The gizzard of some species of herbivorous birds, like turkey and quails,<sup id="cite_ref-:4_66-1" class="reference"><a href="#cite_note-:4-66"><span class="cite-bracket">[</span>66<span class="cite-bracket">]</span></a></sup> contains small pieces of grit or stone called <a href="/wiki/Gastrolith" title="Gastrolith">gastroliths</a> that are swallowed by the bird to aid in the grinding process, serving the function of <a href="/wiki/Teeth" class="mw-redirect" title="Teeth">teeth</a>. The use of gizzard stones is a similarity found between birds and <a href="/wiki/Dinosaur" title="Dinosaur">dinosaurs</a>, which left gastroliths as <a href="/wiki/Trace_fossil" title="Trace fossil">trace fossils</a>.<sup id="cite_ref-:5_67-2" class="reference"><a href="#cite_note-:5-67"><span class="cite-bracket">[</span>67<span class="cite-bracket">]</span></a></sup> </p> <div class="mw-heading mw-heading3"><h3 id="Intestines">Intestines</h3><span class="mw-editsection"><span class="mw-editsection-bracket">[</span><a href="/w/index.php?title=Bird_anatomy&action=edit&section=29" title="Edit section: Intestines"><span>edit</span></a><span class="mw-editsection-bracket">]</span></span></div> <p>The partially digested and pulverized gizzard contents, now called a bolus, are passed into the <a href="/wiki/Intestine" class="mw-redirect" title="Intestine">intestine</a>, where <a href="/wiki/Pancreas#Digestion" title="Pancreas">pancreatic</a> and <a href="/wiki/Digestive_enzymes#Small_intestine" class="mw-redirect" title="Digestive enzymes">intestinal enzymes</a> complete the digestion of the digestible food. The digestion products are then absorbed through the intestinal <a href="/wiki/Mucosa" class="mw-redirect" title="Mucosa">mucosa</a> into the blood. The intestine ends via the large intestine in the vent or <a href="/wiki/Cloaca" title="Cloaca">cloaca</a> which serves as the common exit for renal and intestinal excrements as well as for the laying of eggs.<sup id="cite_ref-storer_71-0" class="reference"><a href="#cite_note-storer-71"><span class="cite-bracket">[</span>71<span class="cite-bracket">]</span></a></sup> However, unlike mammals, many birds do not excrete the bulky portions (roughage) of their undigested food (e.g. feathers, fur, bone fragments, and seed husks) via the cloaca, but regurgitate them as <a href="/wiki/Pellet_(ornithology)" title="Pellet (ornithology)">food pellets</a>.<sup id="cite_ref-72" class="reference"><a href="#cite_note-72"><span class="cite-bracket">[</span>72<span class="cite-bracket">]</span></a></sup><sup id="cite_ref-73" class="reference"><a href="#cite_note-73"><span class="cite-bracket">[</span>73<span class="cite-bracket">]</span></a></sup> </p> <div class="mw-heading mw-heading3"><h3 id="Drinking_behaviour">Drinking behaviour</h3><span class="mw-editsection"><span class="mw-editsection-bracket">[</span><a href="/w/index.php?title=Bird_anatomy&action=edit&section=30" title="Edit section: Drinking behaviour"><span>edit</span></a><span class="mw-editsection-bracket">]</span></span></div> <p>There are three general ways in which birds drink: using gravity itself, sucking, and by using the tongue. Fluid is also obtained from food. </p><p>Most birds are unable to swallow by the "sucking" or "pumping" action of <a href="/wiki/Peristalsis" title="Peristalsis">peristalsis</a> in their <a href="/wiki/Esophagus" title="Esophagus">esophagus</a> (as humans do), and drink by repeatedly raising their heads after filling their mouths to allow the liquid to flow by gravity, a method usually described as "sipping" or "tipping up".<sup id="cite_ref-cade1_74-0" class="reference"><a href="#cite_note-cade1-74"><span class="cite-bracket">[</span>74<span class="cite-bracket">]</span></a></sup> The notable exception is the family of pigeons and doves, the <a href="/wiki/Columbidae" title="Columbidae">Columbidae</a>; in fact, according to <a href="/wiki/Konrad_Lorenz" title="Konrad Lorenz">Konrad Lorenz</a> in 1939: </p> <blockquote><p>one recognizes the order by the single behavioral characteristic, namely that in drinking the water is pumped up by peristalsis of the esophagus which occurs without exception within the order. The only other group, however, which shows the same behavior, the <a href="/wiki/Pteroclidae" class="mw-redirect" title="Pteroclidae">Pteroclidae</a>, is placed near the doves just by this doubtlessly very old characteristic.<sup id="cite_ref-75" class="reference"><a href="#cite_note-75"><span class="cite-bracket">[</span>75<span class="cite-bracket">]</span></a></sup></p></blockquote> <p>Although this general rule still stands, since that time, observations have been made of a few exceptions in both directions.<sup id="cite_ref-cade1_74-1" class="reference"><a href="#cite_note-cade1-74"><span class="cite-bracket">[</span>74<span class="cite-bracket">]</span></a></sup><sup id="cite_ref-76" class="reference"><a href="#cite_note-76"><span class="cite-bracket">[</span>76<span class="cite-bracket">]</span></a></sup> </p><p>In addition, specialized <a href="/wiki/Nectar" title="Nectar">nectar</a> feeders like sunbirds (<a href="/wiki/Nectariniidae" class="mw-redirect" title="Nectariniidae">Nectariniidae</a>) and hummingbirds (<a href="/wiki/Trochilidae" class="mw-redirect" title="Trochilidae">Trochilidae</a>) drink by using protrusible grooved or trough-like tongues, and parrots (<a href="/wiki/Psittacidae" title="Psittacidae">Psittacidae</a>) lap up water.<sup id="cite_ref-cade1_74-2" class="reference"><a href="#cite_note-cade1-74"><span class="cite-bracket">[</span>74<span class="cite-bracket">]</span></a></sup> </p><p>Many seabirds have glands near the eyes that allow them to drink seawater. Excess salt is eliminated from the nostrils. Many desert birds get the water that they need entirely from their food. <a href="/wiki/Uricotelic" class="mw-redirect" title="Uricotelic">The elimination of nitrogenous wastes as uric acid</a> reduces the physiological demand for water,<sup id="cite_ref-77" class="reference"><a href="#cite_note-77"><span class="cite-bracket">[</span>77<span class="cite-bracket">]</span></a></sup> as uric acid is not very toxic and thus does not need to be diluted in as much water.<sup id="cite_ref-Elphick2016_78-0" class="reference"><a href="#cite_note-Elphick2016-78"><span class="cite-bracket">[</span>78<span class="cite-bracket">]</span></a></sup> </p><p><span class="anchor" id="Urogenital_and_Endocrine_systems"></span><span class="anchor" id="Reproductive_system"></span><span class="anchor" id="Reproduction"></span> </p> <div class="mw-heading mw-heading2"><h2 id="Reproductive_and_urogenital_systems">Reproductive and urogenital systems</h2><span class="mw-editsection"><span class="mw-editsection-bracket">[</span><a href="/w/index.php?title=Bird_anatomy&action=edit&section=31" title="Edit section: Reproductive and urogenital systems"><span>edit</span></a><span class="mw-editsection-bracket">]</span></span></div> <figure class="mw-default-size mw-halign-right" typeof="mw:File/Thumb"><a href="/wiki/File:Avian_reproduction.svg" class="mw-file-description"><img src="//upload.wikimedia.org/wikipedia/commons/thumb/a/ab/Avian_reproduction.svg/220px-Avian_reproduction.svg.png" decoding="async" width="220" height="373" class="mw-file-element" srcset="//upload.wikimedia.org/wikipedia/commons/thumb/a/ab/Avian_reproduction.svg/330px-Avian_reproduction.svg.png 1.5x, //upload.wikimedia.org/wikipedia/commons/thumb/a/ab/Avian_reproduction.svg/440px-Avian_reproduction.svg.png 2x" data-file-width="512" data-file-height="868" /></a><figcaption> Seen here is a diagram of a female <a href="/wiki/Chicken" title="Chicken">chicken</a> reproduction system. <span class="nowrap">A. Mature ovum</span>, <span class="nowrap">B. Infundibulum</span>, <span class="nowrap">C. Magnum</span>, <span class="nowrap">D. Isthmus</span>, <span class="nowrap">E. Uterus</span>, <span class="nowrap">F. Vagina</span>, <span class="nowrap">G. Cloaca</span>, <span class="nowrap">H. Large intestine</span>, <span class="nowrap">I. rudiment of right oviduct</span></figcaption></figure> <figure class="mw-default-size" typeof="mw:File/Thumb"><a href="/wiki/File:Bird_sex_-_Two_copulating_ducks_showing_a_corkscrew_penis_inserted_in_a_cloaca_in_Don_Det_Laos.jpg" class="mw-file-description"><img src="//upload.wikimedia.org/wikipedia/commons/thumb/6/6a/Bird_sex_-_Two_copulating_ducks_showing_a_corkscrew_penis_inserted_in_a_cloaca_in_Don_Det_Laos.jpg/220px-Bird_sex_-_Two_copulating_ducks_showing_a_corkscrew_penis_inserted_in_a_cloaca_in_Don_Det_Laos.jpg" decoding="async" width="220" height="147" class="mw-file-element" srcset="//upload.wikimedia.org/wikipedia/commons/thumb/6/6a/Bird_sex_-_Two_copulating_ducks_showing_a_corkscrew_penis_inserted_in_a_cloaca_in_Don_Det_Laos.jpg/330px-Bird_sex_-_Two_copulating_ducks_showing_a_corkscrew_penis_inserted_in_a_cloaca_in_Don_Det_Laos.jpg 1.5x, //upload.wikimedia.org/wikipedia/commons/thumb/6/6a/Bird_sex_-_Two_copulating_ducks_showing_a_corkscrew_penis_inserted_in_a_cloaca_in_Don_Det_Laos.jpg/440px-Bird_sex_-_Two_copulating_ducks_showing_a_corkscrew_penis_inserted_in_a_cloaca_in_Don_Det_Laos.jpg 2x" data-file-width="6435" data-file-height="4290" /></a><figcaption>Copulating ducks showing a corkscrew <a href="/wiki/Penis" title="Penis">penis</a> inserted in a <a href="/wiki/Cloaca" title="Cloaca">cloaca</a>.</figcaption></figure> <figure class="mw-default-size mw-halign-right" typeof="mw:File/Thumb"><a href="/wiki/File:Baby_bird_learning_to_fly.jpg" class="mw-file-description"><img src="//upload.wikimedia.org/wikipedia/commons/thumb/c/c3/Baby_bird_learning_to_fly.jpg/220px-Baby_bird_learning_to_fly.jpg" decoding="async" width="220" height="147" class="mw-file-element" srcset="//upload.wikimedia.org/wikipedia/commons/thumb/c/c3/Baby_bird_learning_to_fly.jpg/330px-Baby_bird_learning_to_fly.jpg 1.5x, //upload.wikimedia.org/wikipedia/commons/thumb/c/c3/Baby_bird_learning_to_fly.jpg/440px-Baby_bird_learning_to_fly.jpg 2x" data-file-width="1600" data-file-height="1067" /></a><figcaption>Fledgling</figcaption></figure> <p>Male birds have two <a href="/wiki/Testicle" title="Testicle">testes</a> which become hundreds of times larger during the <a href="/wiki/Breeding_season" class="mw-redirect" title="Breeding season">breeding season</a> to produce <a href="/wiki/Spermatozoon" title="Spermatozoon">sperm</a>.<sup id="cite_ref-79" class="reference"><a href="#cite_note-79"><span class="cite-bracket">[</span>79<span class="cite-bracket">]</span></a></sup> The testes in birds are generally asymmetric with most birds having a larger left testis.<sup id="cite_ref-80" class="reference"><a href="#cite_note-80"><span class="cite-bracket">[</span>80<span class="cite-bracket">]</span></a></sup> Female birds in most families have only one functional <a href="/wiki/Ovary" title="Ovary">ovary</a> (the left one), connected to an oviduct — although two ovaries are present in the embryonic stage of each female bird. Some species of birds have two functional ovaries, and the <a href="/wiki/Apterygiformes" class="mw-redirect" title="Apterygiformes">kiwis</a> always retain both.<sup id="cite_ref-81" class="reference"><a href="#cite_note-81"><span class="cite-bracket">[</span>81<span class="cite-bracket">]</span></a></sup><sup id="cite_ref-82" class="reference"><a href="#cite_note-82"><span class="cite-bracket">[</span>82<span class="cite-bracket">]</span></a></sup> Birds do not have <a href="/wiki/Male_accessory_gland" title="Male accessory gland">male accessory glands</a>.<sup id="cite_ref-83" class="reference"><a href="#cite_note-83"><span class="cite-bracket">[</span>83<span class="cite-bracket">]</span></a></sup> </p><p>Most male birds have no <a href="/wiki/Bird_penis" class="mw-redirect" title="Bird penis">phallus</a>. In the males of species without a phallus, sperm is stored in the <a href="/wiki/Semen" title="Semen">seminal glomera</a> within the <a href="/wiki/Cloaca" title="Cloaca">cloacal</a> protuberance prior to copulation. During <a href="/wiki/Copulation_(zoology)" title="Copulation (zoology)">copulation</a>, the female moves her tail to the side and the male either mounts the female from behind or in front (as in the <a href="/wiki/Stitchbird" title="Stitchbird">stitchbird</a>), or moves very close to her. The <a href="/wiki/Cloaca" title="Cloaca">cloacae</a> then touch, so that the sperm can enter the female's reproductive tract. This can happen very fast, sometimes in less than half a second.<sup id="cite_ref-84" class="reference"><a href="#cite_note-84"><span class="cite-bracket">[</span>84<span class="cite-bracket">]</span></a></sup> </p><p><a href="/wiki/Female_sperm_storage" title="Female sperm storage">The sperm is stored</a> in the female's sperm storage <a href="/wiki/Tubule" title="Tubule">tubules</a> for a period varying from a week to more than 100 days,<sup id="cite_ref-85" class="reference"><a href="#cite_note-85"><span class="cite-bracket">[</span>85<span class="cite-bracket">]</span></a></sup> depending on the species. Then, eggs will be fertilized individually as they leave the ovaries, before the shell is calcified in the <a href="/wiki/Oviduct" title="Oviduct">oviduct</a>. After the egg is laid by the female, the embryo continues to develop in the egg outside the female body. </p> <figure class="mw-default-size mw-halign-right" typeof="mw:File/Thumb"><a href="/wiki/File:Laughing_Gull_juvenile.jpg" class="mw-file-description"><img src="//upload.wikimedia.org/wikipedia/commons/thumb/5/5d/Laughing_Gull_juvenile.jpg/220px-Laughing_Gull_juvenile.jpg" decoding="async" width="220" height="170" class="mw-file-element" srcset="//upload.wikimedia.org/wikipedia/commons/thumb/5/5d/Laughing_Gull_juvenile.jpg/330px-Laughing_Gull_juvenile.jpg 1.5x, //upload.wikimedia.org/wikipedia/commons/thumb/5/5d/Laughing_Gull_juvenile.jpg/440px-Laughing_Gull_juvenile.jpg 2x" data-file-width="697" data-file-height="540" /></a><figcaption>A juvenile <a href="/wiki/Laughing_gull" title="Laughing gull">laughing gull</a></figcaption></figure> <p>Many <a href="/wiki/Waterfowl" class="mw-redirect" title="Waterfowl">waterfowl</a> and some other birds, such as the <a href="/wiki/Ostrich" title="Ostrich">ostrich</a> and <a href="/wiki/Turkey_(bird)" title="Turkey (bird)">turkey</a>, possess a <a href="/wiki/Bird_penis" class="mw-redirect" title="Bird penis">phallus</a>.<sup id="cite_ref-Jamieson2011_86-0" class="reference"><a href="#cite_note-Jamieson2011-86"><span class="cite-bracket">[</span>86<span class="cite-bracket">]</span></a></sup> This appears to be the ancestral condition among birds; most birds have lost the phallus.<sup id="cite_ref-87" class="reference"><a href="#cite_note-87"><span class="cite-bracket">[</span>87<span class="cite-bracket">]</span></a></sup> The length is thought to be related to <a href="/wiki/Sperm_competition" title="Sperm competition">sperm competition</a> in species that usually mate many times in a breeding season; sperm deposited closer to the ovaries is more likely to achieve fertilization.<sup id="cite_ref-88" class="reference"><a href="#cite_note-88"><span class="cite-bracket">[</span>88<span class="cite-bracket">]</span></a></sup><sup id="cite_ref-Arnqvist_1999_147–156_89-0" class="reference"><a href="#cite_note-Arnqvist_1999_147–156-89"><span class="cite-bracket">[</span>89<span class="cite-bracket">]</span></a></sup> The longer and more complicated phalli tend to occur in waterfowl whose females have unusual anatomical features of the vagina (such as dead end sacs and clockwise coils). These vaginal structures may be used to prevent penetration by the male phallus (which coils counter-clockwise). In these species, copulation is often violent and female co-operation is not required; the female ability to prevent fertilization may allow the female to choose the father for her offspring.<sup id="cite_ref-Arnqvist_1999_147–156_89-1" class="reference"><a href="#cite_note-Arnqvist_1999_147–156-89"><span class="cite-bracket">[</span>89<span class="cite-bracket">]</span></a></sup><sup id="cite_ref-Eberhard_2010_5–18_90-0" class="reference"><a href="#cite_note-Eberhard_2010_5–18-90"><span class="cite-bracket">[</span>90<span class="cite-bracket">]</span></a></sup><sup id="cite_ref-Hosken_2004_87–93_91-0" class="reference"><a href="#cite_note-Hosken_2004_87–93-91"><span class="cite-bracket">[</span>91<span class="cite-bracket">]</span></a></sup><sup id="cite_ref-92" class="reference"><a href="#cite_note-92"><span class="cite-bracket">[</span>92<span class="cite-bracket">]</span></a></sup> When not copulating, the phallus is hidden within the <a href="/wiki/Proctodeum" title="Proctodeum">proctodeum</a> compartment within the cloaca, just inside the vent. </p><p>After the eggs hatch, parents provide varying degrees of care in terms of food and protection. <a href="/wiki/Precocial" class="mw-redirect" title="Precocial">Precocial</a> birds can care for themselves independently within minutes of hatching; <a href="/wiki/Altricial" class="mw-redirect" title="Altricial">altricial</a> hatchlings are helpless, blind, and naked, and require extended parental care. The chicks of many ground-nesting birds such as <a href="/wiki/Partridge" title="Partridge">partridges</a> and <a href="/wiki/Wader" title="Wader">waders</a> are often able to run virtually immediately after hatching; such birds are referred to as <a href="/wiki/Nidifugous" class="mw-redirect" title="Nidifugous">nidifugous</a>. The young of hole-nesters, though, are often totally incapable of unassisted survival. The process whereby a chick acquires feathers until it can fly is called "fledging". </p><p>Some birds, such as pigeons, geese, and <a href="/wiki/Red-crowned_crane" title="Red-crowned crane">red-crowned cranes</a>, remain with their mates for life and may produce offspring on a regular basis. </p> <div class="mw-heading mw-heading3"><h3 id="Kidney">Kidney</h3><span class="mw-editsection"><span class="mw-editsection-bracket">[</span><a href="/w/index.php?title=Bird_anatomy&action=edit&section=32" title="Edit section: Kidney"><span>edit</span></a><span class="mw-editsection-bracket">]</span></span></div> <p>Avian <a href="/wiki/Kidneys" class="mw-redirect" title="Kidneys">kidneys</a> function in almost the same way as the more extensively studied <a href="/wiki/Mammalian_kidney" title="Mammalian kidney">mammalian kidney</a>, but with a few important adaptations; while much of the anatomy remains unchanged in design, some important modifications have occurred during their evolution. </p><p>The three-sectioned kidneys are placed on the bilateral side of the vertebral column, and there are connected to the lower gastrointestinal tract.<sup id="cite_ref-lierz_2003_93-0" class="reference"><a href="#cite_note-lierz_2003-93"><span class="cite-bracket">[</span>93<span class="cite-bracket">]</span></a></sup> Depending on the bird species, the <a href="/wiki/Cortex_(anatomy)" title="Cortex (anatomy)">cortex</a> makes up around 71–80% of the kidney's mass, while the <a href="/wiki/Renal_medulla" title="Renal medulla">medulla</a> is much smaller at about 5–15% of the mass. Blood vessels and other tubes make up the remaining mass. </p><p>Unique to birds is the presence of two different types of <a href="/wiki/Nephrons" class="mw-redirect" title="Nephrons">nephrons</a> (the functional unit of the kidney): both reptilian-like nephrons located in the cortex; and mammalian-like nephrons located in the medulla. Reptilian nephrons are more abundant but lack the distinctive <a href="/wiki/Loop_of_Henle" title="Loop of Henle">loops of Henle</a> seen in mammals. Because of the absence of the loop of Henle in birds, their ability to concentrate water does not depend heavily on it. Water reabsorption depends entirely on the <a href="/wiki/Coprodeum" class="mw-redirect" title="Coprodeum">coprodeum</a> and the rectum.<sup id="cite_ref-Bhul_2012_20-2" class="reference"><a href="#cite_note-Bhul_2012-20"><span class="cite-bracket">[</span>20<span class="cite-bracket">]</span></a></sup> </p><p>The urine collected by the kidney is emptied into the <a href="/wiki/Cloaca" title="Cloaca">cloaca</a> through the ureters and then to the colon by reverse <a href="/wiki/Peristalsis" title="Peristalsis">peristalsis</a>. </p> <figure class="mw-default-size mw-halign-right" typeof="mw:File/Thumb"><a href="/wiki/File:Roseate_Spoonbill_(Ajaia_ajaja)_voiding_in_flight.jpg" class="mw-file-description"><img src="//upload.wikimedia.org/wikipedia/commons/thumb/b/b0/Roseate_Spoonbill_%28Ajaia_ajaja%29_voiding_in_flight.jpg/220px-Roseate_Spoonbill_%28Ajaia_ajaja%29_voiding_in_flight.jpg" decoding="async" width="220" height="147" class="mw-file-element" srcset="//upload.wikimedia.org/wikipedia/commons/thumb/b/b0/Roseate_Spoonbill_%28Ajaia_ajaja%29_voiding_in_flight.jpg/330px-Roseate_Spoonbill_%28Ajaia_ajaja%29_voiding_in_flight.jpg 1.5x, //upload.wikimedia.org/wikipedia/commons/thumb/b/b0/Roseate_Spoonbill_%28Ajaia_ajaja%29_voiding_in_flight.jpg/440px-Roseate_Spoonbill_%28Ajaia_ajaja%29_voiding_in_flight.jpg 2x" data-file-width="8256" data-file-height="5504" /></a><figcaption>A <a href="/wiki/Roseate_spoonbill" title="Roseate spoonbill">Roseate spoonbill</a> excreting urine in flight</figcaption></figure> <figure class="mw-default-size" typeof="mw:File/Thumb"><a href="/wiki/File:Chicken%27s_Kidneys.png" class="mw-file-description"><img src="//upload.wikimedia.org/wikipedia/commons/thumb/6/67/Chicken%27s_Kidneys.png/220px-Chicken%27s_Kidneys.png" decoding="async" width="220" height="293" class="mw-file-element" srcset="//upload.wikimedia.org/wikipedia/commons/thumb/6/67/Chicken%27s_Kidneys.png/330px-Chicken%27s_Kidneys.png 1.5x, //upload.wikimedia.org/wikipedia/commons/thumb/6/67/Chicken%27s_Kidneys.png/440px-Chicken%27s_Kidneys.png 2x" data-file-width="938" data-file-height="1248" /></a><figcaption>Superior (towards the top) is the chicken's head, inferior (towards the bottom) is the chicken's feet. Chicken's kidneys are visualized at the bottom of the abdomen cavity, along the medial spine of the chicken. Testes are labeled as they sit above the kidneys.</figcaption></figure> <div class="mw-heading mw-heading2"><h2 id="Nervous_system">Nervous system</h2><span class="mw-editsection"><span class="mw-editsection-bracket">[</span><a href="/w/index.php?title=Bird_anatomy&action=edit&section=33" title="Edit section: Nervous system"><span>edit</span></a><span class="mw-editsection-bracket">]</span></span></div> <div class="mw-heading mw-heading3"><h3 id="Brain">Brain</h3><span class="mw-editsection"><span class="mw-editsection-bracket">[</span><a href="/w/index.php?title=Bird_anatomy&action=edit&section=34" title="Edit section: Brain"><span>edit</span></a><span class="mw-editsection-bracket">]</span></span></div> <link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1236090951"><div role="note" class="hatnote navigation-not-searchable">Main article: <a href="/wiki/Avian_brain" title="Avian brain">Avian brain</a></div> <div class="excerpt-block"><style data-mw-deduplicate="TemplateStyles:r1066933788">.mw-parser-output .excerpt-hat .mw-editsection-like{font-style:normal}</style><link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1236090951"><div role="note" class="hatnote navigation-not-searchable dablink excerpt-hat selfref">This section is an excerpt from <a href="/wiki/Avian_brain" title="Avian brain">Avian brain</a>.<span class="mw-editsection-like plainlinks"><span class="mw-editsection-bracket">[</span><a class="external text" href="https://en.wikipedia.org/w/index.php?title=Avian_brain&action=edit">edit</a><span class="mw-editsection-bracket">]</span></span></div><div class="excerpt"> <figure typeof="mw:File/Thumb"><a href="/wiki/File:Visual_processing_areas_of_the_brains_of_four_species_of_birds.png" class="mw-file-description"><img src="//upload.wikimedia.org/wikipedia/commons/thumb/e/e1/Visual_processing_areas_of_the_brains_of_four_species_of_birds.png/300px-Visual_processing_areas_of_the_brains_of_four_species_of_birds.png" decoding="async" width="300" height="206" class="mw-file-element" srcset="//upload.wikimedia.org/wikipedia/commons/thumb/e/e1/Visual_processing_areas_of_the_brains_of_four_species_of_birds.png/450px-Visual_processing_areas_of_the_brains_of_four_species_of_birds.png 1.5x, //upload.wikimedia.org/wikipedia/commons/thumb/e/e1/Visual_processing_areas_of_the_brains_of_four_species_of_birds.png/600px-Visual_processing_areas_of_the_brains_of_four_species_of_birds.png 2x" data-file-width="1162" data-file-height="797" /></a><figcaption>Brains of an <a href="/wiki/Emu" title="Emu">emu</a>, a <a href="/wiki/Kiwi_(bird)" title="Kiwi (bird)">kiwi</a>, a <a href="/wiki/Barn-owl" class="mw-redirect" title="Barn-owl">barn owl</a>, and a <a href="/wiki/Rock_dove" title="Rock dove">pigeon</a>, with visual processing areas labelled</figcaption></figure> <p>The <a href="/wiki/Avian_brain" title="Avian brain">avian brain</a> is the central organ of the <a href="/wiki/Nervous_system" title="Nervous system">nervous system</a> in birds. Birds possess large, complex <a href="/wiki/Brain" title="Brain">brains</a>, which <a href="/wiki/Information_processing_(psychology)" title="Information processing (psychology)">process</a>, <a href="/wiki/Information_integration" title="Information integration">integrate</a>, and coordinate information received from the environment and <a href="/wiki/Decision-making" title="Decision-making">make decisions</a> on how to respond with the rest of the body. Like in all <a href="/wiki/Chordate" title="Chordate">chordates</a>, the avian brain is contained within the <a href="/wiki/Skull" title="Skull">skull</a> bones of the <a href="/wiki/Head" title="Head">head</a>. </p><p>The bird brain is divided into a number of sections, each with a different function. The <a href="/wiki/Cerebrum" title="Cerebrum">cerebrum</a> or telencephalon is divided into two <a href="/wiki/Cerebral_hemisphere" title="Cerebral hemisphere">hemispheres</a>, and controls higher functions. The telencephalon is dominated by a large <a href="/wiki/Avian_pallium" title="Avian pallium">pallium</a>, which corresponds to the <a href="/wiki/Mammal" title="Mammal">mammalian</a> <a href="/wiki/Cerebral_cortex" title="Cerebral cortex">cerebral cortex</a> and is responsible for the <a href="/wiki/Cognitive_skill" title="Cognitive skill">cognitive functions</a> of birds. The pallium is made up of several major structures: the hyperpallium, a dorsal bulge of the pallium found only in birds, as well as the nidopallium, mesopallium, and archipallium. The bird telencephalon nuclear structure, wherein neurons are distributed in three-dimensionally arranged clusters, with no large-scale separation of <a href="/wiki/White_matter" title="White matter">white matter</a> and <a href="/wiki/Grey_matter" title="Grey matter">grey matter</a>, though there exist layer-like and column-like connections. Structures in the pallium are associated with <a href="/wiki/Perception" title="Perception">perception</a>, <a href="/wiki/Learning" title="Learning">learning</a>, and <a href="/wiki/Cognition" title="Cognition">cognition</a>. Beneath the pallium are the two components of the subpallium, the <a href="/wiki/Striatum" title="Striatum">striatum</a> and <a href="/wiki/Globus_pallidus" title="Globus pallidus">pallidum</a>. The subpallium connects different parts of the telencephalon and plays major roles in a number of critical behaviours. To the rear of the telencephalon are the <a href="/wiki/Thalamus" title="Thalamus">thalamus</a>, <a href="/wiki/Midbrain" title="Midbrain">midbrain</a>, and <a href="/wiki/Cerebellum" title="Cerebellum">cerebellum</a>. The <a href="/wiki/Hindbrain" title="Hindbrain">hindbrain</a> connects the rest of the brain to the spinal cord. </p> The size and structure of the avian brain enables prominent behaviours of birds such as <a href="/wiki/Bird_flight" title="Bird flight">flight</a> and <a href="/wiki/Bird_vocalization" title="Bird vocalization">vocalization</a>. Dedicated structures and pathways integrate the <a href="/wiki/Hearing" title="Hearing">auditory</a> and <a href="/wiki/Bird_vision" title="Bird vision">visual</a> senses, strong in most species of birds, as well as the typically weaker <a href="/wiki/Sense_of_smell" title="Sense of smell">olfactory</a> and <a href="/wiki/Somatosensory_system" title="Somatosensory system">tactile</a> senses. <a href="/wiki/Social_behavior" title="Social behavior">Social behaviour</a>, widespread among birds, depends on the organisation and functions of the brain. Some birds exhibit strong abilities of cognition, enabled by the unique structure and physiology of the avian brain.</div></div> <p>Birds have a large brain to body mass ratio. This is reflected in the advanced and complex <a href="/wiki/Bird_intelligence" title="Bird intelligence">bird intelligence</a>. </p> <div class="mw-heading mw-heading3"><h3 id="Vision">Vision</h3><span class="mw-editsection"><span class="mw-editsection-bracket">[</span><a href="/w/index.php?title=Bird_anatomy&action=edit&section=35" title="Edit section: Vision"><span>edit</span></a><span class="mw-editsection-bracket">]</span></span></div> <link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1236090951"><div role="note" class="hatnote navigation-not-searchable">Main article: <a href="/wiki/Bird_vision" title="Bird vision">Bird vision</a></div> <p>Birds have acute eyesight—raptors (<a href="/wiki/Birds_of_prey" class="mw-redirect" title="Birds of prey">birds of prey</a>) have vision eight times sharper than humans—thanks to higher densities of photoreceptors in the retina (up to 1,000,000 per square mm in <i><a href="/wiki/Buteo" title="Buteo">Buteos</a></i>, compared to 200,000 for humans), a high number of <a href="/wiki/Neuron" title="Neuron">neurons</a> in the <a href="/wiki/Optic_nerve" title="Optic nerve">optic nerves</a>, a second set of eye muscles not found in other animals, and, in some cases, an indented <a href="/wiki/Fovea_centralis" title="Fovea centralis">fovea</a> which magnifies the central part of the visual field. Many species, including <a href="/wiki/Hummingbird" title="Hummingbird">hummingbirds</a> and <a href="/wiki/Albatross" title="Albatross">albatrosses</a>, have two foveas in each eye. Many birds can detect polarised light. </p> <div class="mw-heading mw-heading3"><h3 id="Hearing">Hearing</h3><span class="mw-editsection"><span class="mw-editsection-bracket">[</span><a href="/w/index.php?title=Bird_anatomy&action=edit&section=36" title="Edit section: Hearing"><span>edit</span></a><span class="mw-editsection-bracket">]</span></span></div> <p>The avian ear is adapted to pick up on slight and rapid changes of pitch found in <a href="/wiki/Bird_Song" class="mw-redirect" title="Bird Song">bird song</a>. General avian <a href="/wiki/Tympanic_membrane" class="mw-redirect" title="Tympanic membrane">tympanic membrane</a> form is ovular and slightly conical. Morphological differences in the <a href="/wiki/Middle_ear" title="Middle ear">middle ear</a> are observed between species. Ossicles within <a href="/wiki/Greenfinch" title="Greenfinch">green finches</a>, <a href="/wiki/Blackbird_(disambiguation)" class="mw-redirect mw-disambig" title="Blackbird (disambiguation)">blackbirds</a>, <a href="/wiki/Song_thrush" title="Song thrush">song thrushes</a>, and <a href="/wiki/House_sparrow" title="House sparrow">house sparrows</a> are proportionately shorter to those found in <a href="/wiki/Pheasant" title="Pheasant">pheasants</a>, <a href="/wiki/Mallard" title="Mallard">Mallard ducks</a>, and <a href="/wiki/Seabird" title="Seabird">sea birds</a>. In song birds, a <a href="/wiki/Syrinx_(bird_anatomy)" title="Syrinx (bird anatomy)">syrinx</a> allows the respective possessors to create intricate melodies and tones. The middle avian ear is made up of three semicircular canals, each ending in an <a href="/wiki/Osseous_ampulla" class="mw-redirect" title="Osseous ampulla">ampulla</a> and joining to connect with the <a href="/wiki/Macula_sacculus" class="mw-redirect" title="Macula sacculus">macula sacculus</a> and <a href="/wiki/Lagena_(anatomy)" title="Lagena (anatomy)">lagena</a>, of which the <a href="/wiki/Cochlea" title="Cochlea">cochlea</a>, a straight short tube to the external ear, branches from.<sup id="cite_ref-94" class="reference"><a href="#cite_note-94"><span class="cite-bracket">[</span>94<span class="cite-bracket">]</span></a></sup> </p><p><br /> </p> <div class="mw-heading mw-heading3"><h3 id="Taste">Taste</h3><span class="mw-editsection"><span class="mw-editsection-bracket">[</span><a href="/w/index.php?title=Bird_anatomy&action=edit&section=37" title="Edit section: Taste"><span>edit</span></a><span class="mw-editsection-bracket">]</span></span></div> <p>Birds evolved from an ancestor that had lost the taste bud type called T1R2, which allows other animals, like alligators, to taste sweet. After many birds adapted to a diet with high sugar content, they modified their <a href="/wiki/Umami" title="Umami">umami</a> taste receptors (T1R1-T1R3) to also sense sweet tastes. TR2, used to detect bitter tastes, is reduced in birds.<sup id="cite_ref-95" class="reference"><a href="#cite_note-95"><span class="cite-bracket">[</span>95<span class="cite-bracket">]</span></a></sup><sup id="cite_ref-96" class="reference"><a href="#cite_note-96"><span class="cite-bracket">[</span>96<span class="cite-bracket">]</span></a></sup> </p> <div class="mw-heading mw-heading2"><h2 id="Immune_system">Immune system</h2><span class="mw-editsection"><span class="mw-editsection-bracket">[</span><a href="/w/index.php?title=Bird_anatomy&action=edit&section=38" title="Edit section: Immune system"><span>edit</span></a><span class="mw-editsection-bracket">]</span></span></div> <link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1236090951"><div role="note" class="hatnote navigation-not-searchable">Main article: <a href="/wiki/Avian_immune_system" title="Avian immune system">Avian immune system</a></div> <p>The <a href="/wiki/Immune_system" title="Immune system">immune system</a> of birds resembles that of other jawed vertebrates. Birds have both <a href="/wiki/Innate_immune_system" title="Innate immune system">innate</a> and <a href="/wiki/Adaptive_immune_system" title="Adaptive immune system">adaptive</a> immune systems. Birds are susceptible to <a href="/wiki/Tumours" class="mw-redirect" title="Tumours">tumours</a>, immune deficiency and autoimmune diseases. </p> <div class="mw-heading mw-heading3"><h3 id="Bursa_of_Fabricius">Bursa of Fabricius</h3><span class="mw-editsection"><span class="mw-editsection-bracket">[</span><a href="/w/index.php?title=Bird_anatomy&action=edit&section=39" title="Edit section: Bursa of Fabricius"><span>edit</span></a><span class="mw-editsection-bracket">]</span></span></div> <figure class="mw-default-size" typeof="mw:File/Thumb"><a href="/wiki/File:Bursa_fabriscius.jpg" class="mw-file-description"><img src="//upload.wikimedia.org/wikipedia/commons/thumb/6/6b/Bursa_fabriscius.jpg/170px-Bursa_fabriscius.jpg" decoding="async" width="170" height="455" class="mw-file-element" srcset="//upload.wikimedia.org/wikipedia/commons/thumb/6/6b/Bursa_fabriscius.jpg/255px-Bursa_fabriscius.jpg 1.5x, //upload.wikimedia.org/wikipedia/commons/thumb/6/6b/Bursa_fabriscius.jpg/340px-Bursa_fabriscius.jpg 2x" data-file-width="648" data-file-height="1736" /></a><figcaption>Internal view of the location of bursa of fabricius</figcaption></figure> <div class="mw-heading mw-heading4"><h4 id="Function">Function</h4><span class="mw-editsection"><span class="mw-editsection-bracket">[</span><a href="/w/index.php?title=Bird_anatomy&action=edit&section=40" title="Edit section: Function"><span>edit</span></a><span class="mw-editsection-bracket">]</span></span></div> <p>The <a href="/wiki/Bursa_of_fabricius" class="mw-redirect" title="Bursa of fabricius">bursa of Fabricius</a>, also known as the cloacal bursa, is a <a href="/wiki/Lymphatic_system#Structure" title="Lymphatic system">lymphoid organ</a> which aids in the production of <a href="/wiki/B_lymphocyte" class="mw-redirect" title="B lymphocyte">B lymphocytes</a> during <a href="/wiki/Humoral_immunity" title="Humoral immunity">humoral immunity</a>. The bursa of Fabricius is present during juvenile stages but curls up. For example, the bursa is not visible after sexual maturity in different species of <a href="/wiki/Old_World_sparrow" title="Old World sparrow">sparrow</a>.<sup id="cite_ref-Anderson06_97-0" class="reference"><a href="#cite_note-Anderson06-97"><span class="cite-bracket">[</span>97<span class="cite-bracket">]</span></a></sup> For comparison, B lymphocytes in mammals are developed in the bone marrow. </p> <div class="mw-heading mw-heading4"><h4 id="Anatomy">Anatomy</h4><span class="mw-editsection"><span class="mw-editsection-bracket">[</span><a href="/w/index.php?title=Bird_anatomy&action=edit&section=41" title="Edit section: Anatomy"><span>edit</span></a><span class="mw-editsection-bracket">]</span></span></div> <p>The bursa of Fabricius is a circular pouch connected to the superior dorsal side of the <a href="/wiki/Cloaca" title="Cloaca">cloaca</a>. The bursa is composed of many folds, known as plica, which are lined by more than 10,000 follicles encompassed by connective tissue and surrounded by <a href="/wiki/Mesenchyme" title="Mesenchyme">mesenchyme</a>. Each follicle consists of a cortex that surrounds a medulla. The cortex houses the highly compacted <a href="/wiki/B_lymphocytes" class="mw-redirect" title="B lymphocytes">B lymphocytes</a>, whereas the medulla houses <a href="/wiki/Lymphocyte" title="Lymphocyte">lymphocytes</a> loosely.<sup id="cite_ref-Anderson06_97-1" class="reference"><a href="#cite_note-Anderson06-97"><span class="cite-bracket">[</span>97<span class="cite-bracket">]</span></a></sup> The medulla is separated from the lumen by the <a href="/wiki/Epithelium" title="Epithelium">epithelium</a> and this aids in the transport of <a href="/wiki/Epithelial_cells" class="mw-redirect" title="Epithelial cells">epithelial cells</a> into the lumen of the bursa. There are 150,000 B lymphocytes located around each follicle.<sup id="cite_ref-98" class="reference"><a href="#cite_note-98"><span class="cite-bracket">[</span>98<span class="cite-bracket">]</span></a></sup> </p> <div class="mw-heading mw-heading2"><h2 id="See_also">See also</h2><span class="mw-editsection"><span class="mw-editsection-bracket">[</span><a href="/w/index.php?title=Bird_anatomy&action=edit&section=42" title="Edit section: See also"><span>edit</span></a><span class="mw-editsection-bracket">]</span></span></div> <style data-mw-deduplicate="TemplateStyles:r1239009302">.mw-parser-output .portalbox{padding:0;margin:0.5em 0;display:table;box-sizing:border-box;max-width:175px;list-style:none}.mw-parser-output .portalborder{border:1px solid var(--border-color-base,#a2a9b1);padding:0.1em;background:var(--background-color-neutral-subtle,#f8f9fa)}.mw-parser-output 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href="#cite_ref-ritchisong_1-1"><sup><i><b>b</b></i></sup></a></span> <span class="reference-text"><style data-mw-deduplicate="TemplateStyles:r1238218222">.mw-parser-output cite.citation{font-style:inherit;word-wrap:break-word}.mw-parser-output .citation q{quotes:"\"""\"""'""'"}.mw-parser-output .citation:target{background-color:rgba(0,127,255,0.133)}.mw-parser-output .id-lock-free.id-lock-free a{background:url("//upload.wikimedia.org/wikipedia/commons/6/65/Lock-green.svg")right 0.1em center/9px no-repeat}.mw-parser-output .id-lock-limited.id-lock-limited a,.mw-parser-output .id-lock-registration.id-lock-registration a{background:url("//upload.wikimedia.org/wikipedia/commons/d/d6/Lock-gray-alt-2.svg")right 0.1em center/9px no-repeat}.mw-parser-output .id-lock-subscription.id-lock-subscription a{background:url("//upload.wikimedia.org/wikipedia/commons/a/aa/Lock-red-alt-2.svg")right 0.1em center/9px no-repeat}.mw-parser-output .cs1-ws-icon a{background:url("//upload.wikimedia.org/wikipedia/commons/4/4c/Wikisource-logo.svg")right 0.1em center/12px no-repeat}body:not(.skin-timeless):not(.skin-minerva) .mw-parser-output .id-lock-free a,body:not(.skin-timeless):not(.skin-minerva) .mw-parser-output .id-lock-limited a,body:not(.skin-timeless):not(.skin-minerva) .mw-parser-output .id-lock-registration a,body:not(.skin-timeless):not(.skin-minerva) .mw-parser-output .id-lock-subscription a,body:not(.skin-timeless):not(.skin-minerva) .mw-parser-output .cs1-ws-icon a{background-size:contain;padding:0 1em 0 0}.mw-parser-output .cs1-code{color:inherit;background:inherit;border:none;padding:inherit}.mw-parser-output .cs1-hidden-error{display:none;color:var(--color-error,#d33)}.mw-parser-output .cs1-visible-error{color:var(--color-error,#d33)}.mw-parser-output .cs1-maint{display:none;color:#085;margin-left:0.3em}.mw-parser-output .cs1-kern-left{padding-left:0.2em}.mw-parser-output .cs1-kern-right{padding-right:0.2em}.mw-parser-output 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New York: Oxford University Press. pp. <a rel="nofollow" class="external text" href="https://archive.org/details/biologyubiquitou00ande/page/n402">390</a>. <a href="/wiki/ISBN_(identifier)" class="mw-redirect" title="ISBN (identifier)">ISBN</a> <a href="/wiki/Special:BookSources/978-0-19-530411-4" title="Special:BookSources/978-0-19-530411-4"><bdi>978-0-19-530411-4</bdi></a>. <a href="/wiki/OCLC_(identifier)" class="mw-redirect" title="OCLC (identifier)">OCLC</a> <a rel="nofollow" class="external text" href="https://search.worldcat.org/oclc/922954367">922954367</a>.</cite><span title="ctx_ver=Z39.88-2004&rft_val_fmt=info%3Aofi%2Ffmt%3Akev%3Amtx%3Abook&rft.genre=book&rft.btitle=Biology+of+the+Ubiquitous+House+Sparrow%3A+From+Genes+to+Populations&rft.place=New+York&rft.pages=390&rft.pub=Oxford+University+Press&rft.date=2006&rft_id=info%3Aoclcnum%2F922954367&rft.isbn=978-0-19-530411-4&rft.aulast=Anderson&rft.aufirst=Ted+R.&rft_id=https%3A%2F%2Farchive.org%2Fdetails%2Fbiologyubiquitou00ande&rfr_id=info%3Asid%2Fen.wikipedia.org%3ABird+anatomy" class="Z3988"></span></span> </li> <li id="cite_note-98"><span class="mw-cite-backlink"><b><a href="#cite_ref-98">^</a></b></span> <span class="reference-text"><link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1238218222"><cite id="CITEREFNagyMagyar2001" class="citation journal cs1">Nagy, N; Magyar, A (March 1, 2001). <a rel="nofollow" class="external text" href="https://doi.org/10.1002%2F1097-0185%2820010301%29262%3A3%3C279%3A%3Aaid-ar1038%3E3.0.co%3B2-i">"Development of the follicle-associated epithelium and the secretory dendritic cell in the bursa of fabricius of the guinea fowl (Numida meleagris) studied by novel monoclonal antibodies"</a>. <i>The Anatomical Record</i>. <b>262</b> (3): 279–292. <a href="/wiki/Doi_(identifier)" class="mw-redirect" title="Doi (identifier)">doi</a>:<span class="id-lock-free" title="Freely accessible"><a rel="nofollow" class="external text" href="https://doi.org/10.1002%2F1097-0185%2820010301%29262%3A3%3C279%3A%3Aaid-ar1038%3E3.0.co%3B2-i">10.1002/1097-0185(20010301)262:3<279::aid-ar1038>3.0.co;2-i</a></span>. <a href="/wiki/PMID_(identifier)" class="mw-redirect" title="PMID (identifier)">PMID</a> <a rel="nofollow" class="external text" href="https://pubmed.ncbi.nlm.nih.gov/11241196">11241196</a>.</cite><span title="ctx_ver=Z39.88-2004&rft_val_fmt=info%3Aofi%2Ffmt%3Akev%3Amtx%3Ajournal&rft.genre=article&rft.jtitle=The+Anatomical+Record&rft.atitle=Development+of+the+follicle-associated+epithelium+and+the+secretory+dendritic+cell+in+the+bursa+of+fabricius+of+the+guinea+fowl+%28Numida+meleagris%29+studied+by+novel+monoclonal+antibodies.&rft.volume=262&rft.issue=3&rft.pages=279-292&rft.date=2001-03-01&rft_id=info%3Adoi%2F10.1002%2F1097-0185%2820010301%29262%3A3%3C279%3A%3Aaid-ar1038%3E3.0.co%3B2-i&rft_id=info%3Apmid%2F11241196&rft.aulast=Nagy&rft.aufirst=N&rft.au=Magyar%2C+A&rft_id=https%3A%2F%2Fdoi.org%2F10.1002%252F1097-0185%252820010301%2529262%253A3%253C279%253A%253Aaid-ar1038%253E3.0.co%253B2-i&rfr_id=info%3Asid%2Fen.wikipedia.org%3ABird+anatomy" class="Z3988"></span></span> </li> </ol></div> <div class="mw-heading mw-heading2"><h2 id="External_links">External links</h2><span class="mw-editsection"><span class="mw-editsection-bracket">[</span><a href="/w/index.php?title=Bird_anatomy&action=edit&section=44" title="Edit section: External links"><span>edit</span></a><span class="mw-editsection-bracket">]</span></span></div> <ul><li><a rel="nofollow" class="external text" href="https://www.biolearners.com/2020/05/Respiration-respiratory-system-respiratory-organs-in-birds.html">Respiratory system and respiratory organs in birds</a></li> <li><a rel="nofollow" class="external text" href="https://web.archive.org/web/20071102171152/http://www.skullsite.com/index.htm">Bird skulls and skeletons</a></li> <li><a rel="nofollow" class="external text" href="http://www.people.eku.edu/ritchisong/birdrespiration.html">The avian respiratory system</a></li> <li><a rel="nofollow" class="external text" href="https://wayback.archive-it.org/all/20150513220607/http://www.vetmed.vt.edu/education/Curriculum/VM8054/Labs/Lab26/lab26.htm">Histology of the avian respiratory system</a></li></ul> <div class="navbox-styles"><style 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class="navbox-group" style="width:1%">Fields</th><td class="navbox-list-with-group navbox-list navbox-odd hlist" style="width:100%;padding:0"><div style="padding:0 0.25em"> <ul><li><a href="/wiki/Gross_anatomy" title="Gross anatomy">Gross anatomy</a></li> <li><a href="/wiki/Superficial_anatomy" class="mw-redirect" title="Superficial anatomy">Superficial anatomy</a></li> <li><a href="/wiki/Neuroanatomy" title="Neuroanatomy">Neuroanatomy</a> <ul><li><a href="/wiki/Brain_morphometry" title="Brain morphometry">brain morphometry</a></li></ul></li> <li><a href="/wiki/Comparative_anatomy" title="Comparative anatomy">Comparative anatomy</a></li> <li>Microscopic anatomy <ul><li><a href="/wiki/Histology" title="Histology">histology</a></li> <li><a href="/wiki/Molecular_anatomy" title="Molecular anatomy">molecular</a></li></ul></li> <li><a href="/wiki/Morphometrics" title="Morphometrics">Morphometrics</a></li></ul> </div></td><td class="noviewer navbox-image" rowspan="9" style="width:1px;padding:0 0 0 2px"><div><span typeof="mw:File"><a href="/wiki/File:ElephantSkelLyd2.png" class="mw-file-description" title="Endoskeleton of an elephant"><img alt="Endoskeleton of an elephant" src="//upload.wikimedia.org/wikipedia/commons/thumb/7/74/ElephantSkelLyd2.png/140px-ElephantSkelLyd2.png" decoding="async" width="140" height="113" class="mw-file-element" srcset="//upload.wikimedia.org/wikipedia/commons/thumb/7/74/ElephantSkelLyd2.png/210px-ElephantSkelLyd2.png 1.5x, //upload.wikimedia.org/wikipedia/commons/thumb/7/74/ElephantSkelLyd2.png/280px-ElephantSkelLyd2.png 2x" data-file-width="778" data-file-height="626" /></a></span></div></td></tr><tr><th scope="row" class="navbox-group" style="width:1%">Bacteria and fungi</th><td class="navbox-list-with-group navbox-list navbox-even hlist" style="width:100%;padding:0"><div style="padding:0 0.25em"> <ul><li><a href="/wiki/Bacterial_cell_structure" title="Bacterial cell structure">Bacterial cell structure</a> <ul><li><a href="/wiki/Bacterial_cellular_morphologies" title="Bacterial cellular morphologies">cellular morphologies</a></li> <li><a href="/wiki/Bacterial_morphological_plasticity" title="Bacterial morphological plasticity">morphological plasticity</a></li></ul></li> <li><a href="/wiki/Colonial_morphology" title="Colonial morphology">Colonial morphology</a></li> <li><a href="/wiki/Lichen_morphology" title="Lichen morphology">Lichen morphology</a></li></ul> </div></td></tr><tr><th scope="row" class="navbox-group" style="width:1%">Protists</th><td class="navbox-list-with-group navbox-list navbox-odd hlist" style="width:100%;padding:0"><div style="padding:0 0.25em"> <ul><li><a href="/wiki/Template:Protist_structures" title="Template:Protist structures">Structures</a></li></ul> </div></td></tr><tr><th scope="row" class="navbox-group" style="width:1%">Plants</th><td class="navbox-list-with-group navbox-list navbox-even hlist" style="width:100%;padding:0"><div style="padding:0 0.25em"> <ul><li><a href="/wiki/Plant_anatomy" title="Plant anatomy">Plant anatomy</a> <ul><li><a href="/wiki/Fruit_anatomy" class="mw-redirect" title="Fruit anatomy">fruit</a></li></ul></li> <li><a href="/wiki/Plant_habit" class="mw-redirect" title="Plant habit">Plant habit</a></li> <li><a href="/wiki/Plant_life-form" title="Plant life-form">Plant life-form</a></li> <li><a href="/wiki/Plant_morphology" title="Plant morphology">Plant morphology</a> <ul><li><a href="/wiki/Plant_reproductive_morphology" title="Plant reproductive morphology">reproductive</a></li></ul></li> <li><a href="/wiki/Soil_morphology" title="Soil morphology">Soil morphology</a></li></ul> </div></td></tr><tr><th scope="row" class="navbox-group" style="width:1%">Invertebrates</th><td class="navbox-list-with-group navbox-list navbox-odd hlist" style="width:100%;padding:0"><div style="padding:0 0.25em"> <ul><li><a href="/wiki/Decapod_anatomy" title="Decapod anatomy">Decapod anatomy</a></li> <li><a href="/wiki/Gastropoda#Anatomy" title="Gastropoda">Gastropod anatomy</a></li> <li><a href="/wiki/Insect_morphology" title="Insect morphology">Insect morphology</a> <ul><li><a href="/wiki/Morphology_of_Diptera" title="Morphology of Diptera">Diptera</a></li> <li><a href="/wiki/External_morphology_of_Odonata" title="External morphology of Odonata">Odonata</a></li></ul></li> <li><a href="/wiki/Spider_anatomy" title="Spider anatomy">Spider anatomy</a></li> <li><a href="/wiki/Arthropod_cuticle" class="mw-redirect" title="Arthropod cuticle">Arthropod cuticle</a></li></ul> </div></td></tr><tr><th scope="row" class="navbox-group" style="width:1%"><a href="/wiki/Mammal_anatomy" class="mw-redirect" title="Mammal anatomy">Mammals</a></th><td class="navbox-list-with-group navbox-list navbox-even hlist" style="width:100%;padding:0"><div style="padding:0 0.25em"> <ul><li><a href="/wiki/Human_anatomy" class="mw-redirect" title="Human anatomy">Human anatomy</a></li> <li><a href="/wiki/Neanderthal_anatomy" title="Neanderthal anatomy">Neanderthal anatomy</a></li> <li><a href="/wiki/Cat_anatomy" title="Cat anatomy">Cat anatomy</a></li> <li><a href="/wiki/Dog_anatomy" title="Dog anatomy">Dog anatomy</a></li> <li><a href="/wiki/Equine_anatomy" title="Equine anatomy">Horse anatomy</a></li> <li><a href="/wiki/Elephant#Anatomy_and_morphology" title="Elephant">Elephant anatomy</a></li> <li><a href="/wiki/Giraffe#Appearance_and_anatomy" title="Giraffe">Giraffe anatomy</a></li></ul> </div></td></tr><tr><th scope="row" class="navbox-group" style="width:1%"><a href="/wiki/Vertebrate_anatomy" class="mw-redirect" title="Vertebrate anatomy">Other vertebrates</a></th><td class="navbox-list-with-group navbox-list navbox-odd hlist" style="width:100%;padding:0"><div style="padding:0 0.25em"> <ul><li><a href="/wiki/Amphibian_anatomy" class="mw-redirect" title="Amphibian anatomy">Amphibian anatomy</a></li> <li><a class="mw-selflink selflink">Bird anatomy</a></li> <li><a href="/wiki/Fish_anatomy" title="Fish anatomy">Fish anatomy</a></li> <li><a href="/wiki/Shark_anatomy" title="Shark anatomy">Shark anatomy</a></li></ul> </div></td></tr><tr><th scope="row" class="navbox-group" style="width:1%">Glossaries</th><td class="navbox-list-with-group navbox-list navbox-even hlist" style="width:100%;padding:0"><div style="padding:0 0.25em"> <ul><li><a href="/wiki/Anatomical_terminology" title="Anatomical terminology">Anatomical terminology</a></li> <li><a href="/wiki/Anatomical_terms_of_location" title="Anatomical terms of location">Anatomical terms of location</a></li> <li><a href="/wiki/Glossary_of_dinosaur_anatomy" title="Glossary of dinosaur anatomy">Glossary of dinosaur anatomy</a></li> <li><a href="/wiki/Glossary_of_plant_morphology" title="Glossary of plant morphology">Glossary of plant morphology</a> <ul><li><a href="/wiki/Glossary_of_leaf_morphology" title="Glossary of leaf morphology">leaf morphology</a></li></ul></li></ul> </div></td></tr><tr><th scope="row" class="navbox-group" style="width:1%">Related topics</th><td class="navbox-list-with-group navbox-list navbox-odd hlist" style="width:100%;padding:0"><div style="padding:0 0.25em"> <ul><li><a href="/wiki/Allometry" title="Allometry">Allometry</a></li> <li><a href="/wiki/Anatomical_variation" title="Anatomical variation">Anatomical variation</a></li> <li><a href="/wiki/Anatomical_plane" title="Anatomical plane">Anatomical plane</a></li> <li><a href="/wiki/Body_plan" title="Body plan">Body plan</a></li> <li><a href="/wiki/Form_classification" title="Form classification">Form classification</a></li> <li><a href="/wiki/Gracility" title="Gracility">Gracility</a></li> <li><a href="/wiki/Hertwig_rule" title="Hertwig rule">Hertwig rule</a></li> <li><a href="/wiki/History_of_anatomy" title="History of anatomy">History of anatomy</a> <ul><li><a href="/wiki/History_of_anatomy_in_the_19th_century" title="History of anatomy in the 19th century">19th century</a></li></ul></li> <li><a href="/wiki/Physiognomy" title="Physiognomy">Physiognomy</a></li> <li><a href="/wiki/Standard_anatomical_position" title="Standard anatomical position">Standard anatomical position</a></li> <li><a href="/wiki/Transcendental_anatomy" title="Transcendental anatomy">Transcendental anatomy</a></li></ul> </div></td></tr><tr><td class="navbox-abovebelow hlist" colspan="3"><div> <ul><li><span class="noviewer" typeof="mw:File"><span title="Category"><img alt="" src="//upload.wikimedia.org/wikipedia/en/thumb/9/96/Symbol_category_class.svg/16px-Symbol_category_class.svg.png" decoding="async" width="16" height="16" class="mw-file-element" srcset="//upload.wikimedia.org/wikipedia/en/thumb/9/96/Symbol_category_class.svg/23px-Symbol_category_class.svg.png 1.5x, //upload.wikimedia.org/wikipedia/en/thumb/9/96/Symbol_category_class.svg/31px-Symbol_category_class.svg.png 2x" data-file-width="180" data-file-height="185" /></span></span> <a href="/wiki/Category:Anatomy" title="Category:Anatomy">Category</a></li> <li><span class="noviewer" typeof="mw:File"><a href="/wiki/File:Symbol_portal_class.svg" class="mw-file-description" title="Portal"><img alt="" src="//upload.wikimedia.org/wikipedia/en/thumb/e/e2/Symbol_portal_class.svg/16px-Symbol_portal_class.svg.png" decoding="async" width="16" height="16" class="mw-file-element" srcset="//upload.wikimedia.org/wikipedia/en/thumb/e/e2/Symbol_portal_class.svg/23px-Symbol_portal_class.svg.png 1.5x, //upload.wikimedia.org/wikipedia/en/thumb/e/e2/Symbol_portal_class.svg/31px-Symbol_portal_class.svg.png 2x" data-file-width="180" data-file-height="185" /></a></span> <a href="/wiki/Portal:Anatomy" title="Portal:Anatomy">Portal</a></li> <li><a href="/wiki/Index_of_anatomy_articles" title="Index of anatomy articles">Index of anatomy articles</a></li></ul> </div></td></tr></tbody></table></div> <div class="navbox-styles"><link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1129693374"><link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1236075235"></div><div role="navigation" class="navbox" aria-labelledby="Birds_(class:_Aves)" style="padding:3px"><table class="nowraplinks hlist mw-collapsible autocollapse navbox-inner" style="border-spacing:0;background:transparent;color:inherit"><tbody><tr><th scope="col" class="navbox-title" colspan="2"><link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1129693374"><link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1239400231"><div class="navbar plainlinks hlist navbar-mini"><ul><li class="nv-view"><a href="/wiki/Template:Birds" title="Template:Birds"><abbr title="View this template">v</abbr></a></li><li class="nv-talk"><a href="/wiki/Template_talk:Birds" title="Template talk:Birds"><abbr title="Discuss this template">t</abbr></a></li><li class="nv-edit"><a href="/wiki/Special:EditPage/Template:Birds" title="Special:EditPage/Template:Birds"><abbr title="Edit this template">e</abbr></a></li></ul></div><div id="Birds_(class:_Aves)" style="font-size:114%;margin:0 4em"><a href="/wiki/Bird" title="Bird">Birds</a> (<a href="/wiki/Class_(biology)" title="Class (biology)">class</a>: Aves)</div></th></tr><tr><td class="navbox-abovebelow" colspan="2"><div> <ul><li><a href="/wiki/Outline_of_birds" title="Outline of birds">Outline</a></li></ul> </div></td></tr><tr><th scope="row" class="navbox-group" style="width:1%"><a class="mw-selflink selflink">Anatomy</a></th><td class="navbox-list-with-group navbox-list navbox-odd" style="width:100%;padding:0"><div style="padding:0 0.25em"> <ul><li><a href="/wiki/Beak" title="Beak">Beak</a></li> <li><a href="/wiki/Avian_brain" title="Avian brain">Brain</a></li> <li><a href="/wiki/Crop_(anatomy)#Birds" title="Crop (anatomy)">Crop</a> <ul><li><a href="/wiki/Crop_milk" title="Crop milk">milk</a></li></ul></li> <li><a href="/wiki/Dactyly#bird_digits" title="Dactyly">Dactyly</a></li> <li><a href="/wiki/Egg" title="Egg">Eggs</a></li> <li><a href="/wiki/Feather" title="Feather">Feathers</a></li> <li><a href="/wiki/Bird_flight" title="Bird flight">Flight</a></li> <li><a href="/wiki/Uropygial_gland" title="Uropygial gland">Preen gland</a></li> <li><a href="/wiki/Plumage" title="Plumage">Plumage</a></li> <li><a href="/wiki/Bird_vision" title="Bird vision">Vision</a></li></ul> </div></td></tr><tr><th scope="row" class="navbox-group" style="width:1%"><a href="/wiki/Bird_behaviour" class="mw-redirect" title="Bird behaviour">Behaviour</a></th><td class="navbox-list-with-group navbox-list navbox-even" style="width:100%;padding:0"><div style="padding:0 0.25em"> <ul><li><a href="/wiki/Bird_vocalization" title="Bird vocalization">Singing</a></li> <li><a href="/wiki/Bird_intelligence" title="Bird intelligence">Intelligence</a></li> <li><a href="/wiki/Bird_migration" title="Bird migration">Migration</a></li> <li><a href="/wiki/Avian_foraging" title="Avian foraging">Foraging</a></li> <li><a href="/wiki/Sexual_selection_in_birds" title="Sexual selection in birds">Sexual selection</a></li> <li><a href="/wiki/Lek_mating" title="Lek mating">Lek mating</a></li> <li><a href="/wiki/Seabird_breeding_behavior" title="Seabird breeding behavior">Seabird breeding</a></li> <li><a href="/wiki/Egg_incubation#Avian_incubation" title="Egg incubation">Incubation</a></li> <li><a href="/wiki/Brood_parasite" class="mw-redirect" title="Brood parasite">Brood parasites</a></li> <li><a href="/wiki/Bird_nest" title="Bird nest">Nesting</a></li> <li><a href="/wiki/Bird_hybrid" title="Bird hybrid">Hybrids</a></li> <li><a href="/wiki/Bird_colony" title="Bird colony">Colony</a></li></ul> </div></td></tr><tr><th scope="row" class="navbox-group" style="width:1%"><a href="/wiki/Evolution" title="Evolution">Evolution</a></th><td class="navbox-list-with-group navbox-list navbox-odd" style="width:100%;padding:0"><div style="padding:0 0.25em"> <ul><li><a href="/wiki/Origin_of_birds" title="Origin of birds">Origin of birds</a> <ul><li><a href="/wiki/Theropoda" title="Theropoda">Theropoda</a></li> <li><a href="/wiki/Dinosaur" title="Dinosaur">dinosaurs</a></li></ul></li> <li><a href="/wiki/Origin_of_avian_flight" title="Origin of avian flight">Origin of flight</a></li> <li><a href="/wiki/Evolution_of_birds" title="Evolution of birds">Evolution of birds</a></li> <li><a href="/wiki/Darwin%27s_finches" title="Darwin's finches">Darwin's finches</a></li> <li><a href="/wiki/Seabird" title="Seabird">Seabirds</a></li></ul> </div></td></tr><tr><th scope="row" class="navbox-group" style="width:1%"><a href="/wiki/List_of_fossil_bird_genera" title="List of fossil bird genera">Fossil birds</a></th><td class="navbox-list-with-group navbox-list navbox-even" style="width:100%;padding:0"><div style="padding:0 0.25em"> <ul><li><i><a href="/wiki/Archaeopteryx" title="Archaeopteryx">Archaeopteryx</a></i></li> <li><a href="/wiki/Omnivoropterygidae" title="Omnivoropterygidae">Omnivoropterygiformes</a></li> <li><a href="/wiki/Jeholornithidae" title="Jeholornithidae">Jeholornithidae</a></li> <li><a href="/wiki/Confuciusornithiformes" class="mw-redirect" title="Confuciusornithiformes">Confuciusornithiformes</a></li> <li><a href="/wiki/Enantiornithes" title="Enantiornithes">Enantiornithes</a></li> <li><a href="/wiki/Chaoyangiformes" class="mw-redirect" title="Chaoyangiformes">Chaoyangiformes</a></li> <li><a href="/wiki/Patagopterygiformes" title="Patagopterygiformes">Patagopterygiformes</a></li> <li><a href="/wiki/Ambiortiformes" title="Ambiortiformes">Ambiortiformes</a></li> <li><a href="/wiki/Songlingornithiformes" class="mw-redirect" title="Songlingornithiformes">Songlingornithiformes</a></li> <li><a href="/wiki/Hongshanornithidae" title="Hongshanornithidae">Hongshanornithidae</a></li> <li><a href="/wiki/Gansus" title="Gansus">Gansuiformes</a></li> <li><a href="/wiki/Ichthyornithes" title="Ichthyornithes">Ichthyornithiformes</a></li> <li><a href="/wiki/Hesperornithes" title="Hesperornithes">Hesperornithes</a></li> <li><a href="/wiki/Lithornithidae" title="Lithornithidae">Lithornithiformes</a></li> <li><a href="/wiki/Moa" title="Moa">Dinornithiformes</a></li> <li><a href="/wiki/Elephant_bird" title="Elephant bird">Aepyornithiformes</a></li> <li><a href="/wiki/Gastornithiformes" title="Gastornithiformes">Gastornithiformes</a></li></ul> </div></td></tr><tr><th scope="row" class="navbox-group" style="width:1%"><a href="/wiki/Human_uses_of_birds" title="Human uses of birds">Human <br />interaction</a></th><td class="navbox-list-with-group navbox-list navbox-odd" style="width:100%;padding:0"><div style="padding:0 0.25em"> <ul><li><a href="/wiki/Bird_ringing" title="Bird ringing">Ringing</a></li> <li><a href="/wiki/Ornithology" title="Ornithology">Ornithology</a></li> <li><a href="/wiki/Ornithomancy" title="Ornithomancy">Ornithomancy</a></li> <li><a href="/wiki/Bird_collections" title="Bird collections">Bird collections</a></li> <li><a href="/wiki/Birdwatching" title="Birdwatching">Birdwatching</a> <ul><li><a href="/wiki/Big_year" title="Big year">big year</a></li></ul></li> <li><a href="/wiki/Bird_feeding" title="Bird feeding">Bird feeding</a></li> <li><a href="/wiki/Bird_conservation" title="Bird conservation">Conservation</a></li> <li><a href="/wiki/Aviculture" title="Aviculture">Aviculture</a></li> <li><a href="/wiki/Waterfowl_hunting" title="Waterfowl hunting">Waterfowl hunting</a></li> <li><a href="/wiki/Cockfight" class="mw-redirect" title="Cockfight">Cockfighting</a></li> <li><a href="/wiki/Pigeon_racing" title="Pigeon racing">Pigeon racing</a></li> <li><a href="/wiki/Falconry" title="Falconry">Falconry</a></li> <li><a href="/wiki/Pheasantry" title="Pheasantry">Pheasantry</a></li> <li><a href="/wiki/Imping" title="Imping">Imping</a></li> <li><a href="/wiki/Oology" title="Oology">Egg collecting</a></li></ul> </div></td></tr><tr><th scope="row" class="navbox-group" style="width:1%">Lists</th><td class="navbox-list-with-group navbox-list navbox-even" style="width:100%;padding:0"><div style="padding:0 0.25em"> <ul><li><a href="/wiki/List_of_birds" title="List of birds">Families and orders</a></li> <li><a href="/wiki/List_of_bird_genera" title="List of bird genera">Genera</a></li> <li><a href="/wiki/Glossary_of_bird_terms" title="Glossary of bird terms">Glossary of bird terms</a></li> <li><a href="/wiki/List_of_birds_by_population" title="List of birds by population">List by population</a></li> <li><a href="/wiki/Lists_of_birds_by_region" title="Lists of birds by region">Lists by region</a></li> <li><a href="/wiki/List_of_extinct_bird_species_since_1500" title="List of extinct bird species since 1500">Extinct species since 1500</a></li> <li><a href="/wiki/List_of_Late_Quaternary_prehistoric_bird_species" title="List of Late Quaternary prehistoric bird species">Late Quaternary prehistoric birds</a></li> <li>Notable birds <ul><li><a href="/wiki/List_of_individual_birds" title="List of individual birds">individuals</a></li> <li><a href="/wiki/List_of_fictional_birds" title="List of fictional birds">fictional</a></li></ul></li></ul> </div></td></tr><tr><td colspan="2" class="navbox-list navbox-odd" style="width:100%;padding:0"><div style="padding:0 0.25em"></div><table class="nowraplinks navbox-subgroup" style="border-spacing:0"><tbody><tr><td colspan="2" class="navbox-list navbox-odd" style="width:100%;padding:0"><div style="padding:0 0.25em"></div><table class="nowraplinks mw-collapsible mw-collapsed navbox-subgroup" style="border-spacing:0"><tbody><tr><th scope="col" class="navbox-title" colspan="2"><div id="Neornithes" style="font-size:114%;margin:0 4em">Neornithes</div></th></tr><tr><td colspan="2" class="navbox-list navbox-odd" style="width:100%;padding:0"><div style="padding:0 0.25em"></div><table class="nowraplinks navbox-subgroup" style="border-spacing:0"><tbody><tr><td colspan="2" class="navbox-list navbox-odd" style="width:100%;padding:0"><div style="padding:0 0.25em"></div><table class="nowraplinks navbox-subgroup" style="border-spacing:0"><tbody><tr><th id="Palaeognathae" scope="row" class="navbox-group" style="width:1%"><a href="/wiki/Palaeognathae" title="Palaeognathae">Palaeognathae</a></th><td class="navbox-list-with-group navbox-list navbox-odd" style="width:100%;padding:0"><div style="padding:0 0.25em"> <ul><li><a href="/wiki/Struthionidae" title="Struthionidae">Struthioniformes <span style="font-size:85%;">(ostriches)</span></a></li> <li><a href="/wiki/Rheidae" title="Rheidae">Rheiformes <span style="font-size:85%;">(rheas)</span></a></li> <li><a href="/wiki/Tinamou" title="Tinamou">Tinamiformes <span style="font-size:85%;">(tinamous)</span></a></li> <li><a href="/wiki/Kiwi_(bird)" title="Kiwi (bird)">Apterygiformes <span style="font-size:85%;">(kiwis)</span></a></li> <li><a href="/wiki/Casuariiformes" title="Casuariiformes">Casuariiformes <span style="font-size:85%;">(emus and cassowaries)</span></a></li></ul> </div></td></tr></tbody></table><div></div></td></tr><tr><td colspan="2" class="navbox-list navbox-odd" style="width:100%;padding:0"><div style="padding:0 0.25em"></div><table class="nowraplinks navbox-subgroup" style="border-spacing:0"><tbody><tr><th scope="row" class="navbox-group" style="width:1%"><a href="/wiki/Neognathae" title="Neognathae">N<br />e<br />o<br />g<br />n<br />a<br />t<br />h<br />a<br />e</a></th><td class="navbox-list-with-group navbox-list navbox-odd" style="width:100%;padding:0"><div style="padding:0 0.25em"></div><table class="nowraplinks navbox-subgroup" style="border-spacing:0"><tbody><tr><td colspan="2" class="navbox-list navbox-odd" style="width:100%;padding:0"><div style="padding:0 0.25em"></div><table class="nowraplinks navbox-subgroup" style="border-spacing:0"><tbody><tr><th id="Galloanserae_(fowls)" scope="row" class="navbox-group" style="width:1%"><a href="/wiki/Galloanserae" class="mw-redirect" title="Galloanserae">G<br />a<br />l<br />l<br />o<br />a<br />n<br />s<br />e<br />r<br />a<br />e</a> <br /> <span style="font-size:85%;">(<a href="/wiki/Fowl" title="Fowl">fowls</a>)</span></th><td class="navbox-list-with-group navbox-list navbox-odd" style="width:100%;padding:0"><div style="padding:0 0.25em"></div><table class="nowraplinks navbox-subgroup" style="border-spacing:0"><tbody><tr><th scope="row" class="navbox-group" style="width:1%"><a href="/wiki/Anseriformes" title="Anseriformes">Anseriformes</a> <br /> <span style="font-size:85%;">(waterfowls)</span></th><td class="navbox-list-with-group navbox-list navbox-odd" style="width:100%;padding:0"><div style="padding:0 0.25em"></div><table class="nowraplinks navbox-subgroup" style="border-spacing:0"><tbody><tr><th scope="row" class="navbox-group" style="width:1%"><a href="/wiki/Anatidae" title="Anatidae">Anatidae</a> <br /> <span style="font-size:85%;">(<a href="/wiki/Duck" title="Duck">ducks</a>)</span></th><td class="navbox-list-with-group navbox-list navbox-even" style="width:100%;padding:0"><div style="padding:0 0.25em"> <ul><li><a href="/wiki/Anatinae" title="Anatinae">Anatinae</a> <ul><li><a href="/wiki/Diving_duck" title="Diving duck">Aythyini</a></li> <li><a href="/wiki/Mergini" title="Mergini">Mergini</a></li> <li><a href="/wiki/Oxyurini" title="Oxyurini">Oxyurini</a></li></ul></li> <li><a href="/wiki/Anserinae" title="Anserinae">Anserinae</a> <ul><li><a href="/wiki/Swan" title="Swan"><span style="font-size:85%;">swans</span></a></li> <li><a href="/wiki/Goose" title="Goose"><span style="font-size:85%;">true geese</span></a></li></ul></li> <li><a href="/wiki/Whistling_duck" title="Whistling duck">Dendrocygninae</a></li> <li><a href="/wiki/Freckled_duck" title="Freckled duck">Stictonettinae</a></li> <li><a href="/wiki/Tadorninae" title="Tadorninae">Tadorninae</a></li></ul> </div></td></tr><tr><th scope="row" class="navbox-group" style="width:1%"><a href="/wiki/Anhimidae" class="mw-redirect" title="Anhimidae">Anhimidae</a></th><td class="navbox-list-with-group navbox-list navbox-odd" style="width:100%;padding:0"><div style="padding:0 0.25em"> <ul><li><i><a href="/wiki/Horned_screamer" title="Horned screamer">Anhima</a></i></li> <li><i><a href="/wiki/Chauna" title="Chauna">Chauna</a></i></li></ul> </div></td></tr><tr><th scope="row" class="navbox-group" style="width:1%"><a href="/wiki/Anseranatidae" title="Anseranatidae">Anseranatidae</a></th><td class="navbox-list-with-group navbox-list navbox-even" style="width:100%;padding:0"><div style="padding:0 0.25em"> <ul><li><i><a href="/wiki/Magpie_goose" title="Magpie goose">Anseranas</a></i></li></ul> </div></td></tr></tbody></table><div></div></td></tr><tr><th scope="row" class="navbox-group" style="width:1%"><a href="/wiki/Galliformes" title="Galliformes">Galliformes</a> <br /> <span style="font-size:85%;">(<a href="/wiki/Landfowl" class="mw-redirect" title="Landfowl">landfowls</a>-</span> <br /> <span style="font-size:85%;"><a href="/wiki/Gamebirds" class="mw-redirect" title="Gamebirds">gamebirds</a>)</span></th><td class="navbox-list-with-group navbox-list navbox-odd" style="width:100%;padding:0"><div style="padding:0 0.25em"></div><table class="nowraplinks navbox-subgroup" style="border-spacing:0"><tbody><tr><th scope="row" class="navbox-group" style="width:1%"><a href="/wiki/Cracidae" title="Cracidae">Cracidae</a></th><td class="navbox-list-with-group navbox-list navbox-odd" style="width:100%;padding:0"><div style="padding:0 0.25em"> <ul><li><a href="/wiki/Cracinae" class="mw-redirect" title="Cracinae">Cracinae</a></li> <li><a href="/wiki/Oreophasinae" class="mw-redirect" title="Oreophasinae">Oreophasinae</a></li> <li><a href="/wiki/Penelopinae" class="mw-redirect" title="Penelopinae">Penelopinae</a></li></ul> </div></td></tr><tr><th scope="row" class="navbox-group" style="width:1%"><a href="/wiki/Megapodidae" class="mw-redirect" title="Megapodidae">Megapodidae</a></th><td class="navbox-list-with-group navbox-list navbox-even" style="width:100%;padding:0"><div style="padding:0 0.25em"> <ul><li><i><a href="/wiki/Aepypodius" title="Aepypodius">Aepypodius</a></i></li> <li><i><a href="/wiki/Alectura" class="mw-redirect" title="Alectura">Alectura</a></i></li> <li><i><a href="/wiki/Eulipoa" class="mw-redirect" title="Eulipoa">Eulipoa</a></i></li> <li><i><a href="/wiki/Leipoa" class="mw-redirect" title="Leipoa">Leipoa</a></i></li> <li><i><a href="/wiki/Macrocephalon" class="mw-redirect" title="Macrocephalon">Macrocephalon</a></i></li> <li><i><a href="/wiki/Megapodius" class="mw-redirect" title="Megapodius">Megapodius</a></i></li> <li><i><a href="/wiki/Talegalla" title="Talegalla">Talegalla</a></i></li></ul> </div></td></tr><tr><th scope="row" class="navbox-group" style="width:1%"><a href="/wiki/Numididae" class="mw-redirect" title="Numididae">Numididae</a></th><td class="navbox-list-with-group navbox-list navbox-odd" style="width:100%;padding:0"><div style="padding:0 0.25em"> <ul><li><i><a href="/wiki/Vulturine_guineafowl" title="Vulturine guineafowl">Acryllium</a></i></li> <li><i><a href="/wiki/Agelastes" title="Agelastes">Agelastes</a></i></li> <li><i><a href="/wiki/Guttera" title="Guttera">Guttera</a></i></li> <li><i><a href="/wiki/Numida" class="mw-redirect" title="Numida">Numida</a></i></li></ul> </div></td></tr><tr><th scope="row" class="navbox-group" style="width:1%"><a href="/wiki/Odontophoridae" class="mw-redirect" title="Odontophoridae">Odontophoridae</a></th><td class="navbox-list-with-group navbox-list navbox-even" style="width:100%;padding:0"><div style="padding:0 0.25em"> <ul><li><i><a href="/wiki/Callipepla" title="Callipepla">Callipepla</a></i></li> <li><i><a href="/wiki/Colinus" title="Colinus">Colinus</a></i></li> <li><i><a href="/wiki/Cyrtonyx" title="Cyrtonyx">Cyrtonyx</a></i></li> <li><i><a href="/wiki/Dactylortyx" class="mw-redirect" title="Dactylortyx">Dactylortyx</a></i></li> <li><i><a href="/wiki/Dendrortyx" title="Dendrortyx">Dendrortyx</a></i></li> <li><i><a href="/wiki/Odontophorus" class="mw-redirect" title="Odontophorus">Odontophorus</a></i></li> <li><i><a href="/wiki/Oreortyx" class="mw-redirect" title="Oreortyx">Oreortyx</a></i></li> <li><i><a href="/wiki/Philortyx" class="mw-redirect" title="Philortyx">Philortyx</a></i></li> <li><i><a href="/wiki/Rhynchortyx" class="mw-redirect" title="Rhynchortyx">Rhynchortyx</a></i></li></ul> </div></td></tr><tr><th scope="row" class="navbox-group" style="width:1%"><a href="/wiki/Phasianidae" title="Phasianidae">Phasianidae</a></th><td class="navbox-list-with-group navbox-list navbox-odd" style="width:100%;padding:0"><div style="padding:0 0.25em"> <ul><li><a href="/wiki/Meleagridinae" class="mw-redirect" title="Meleagridinae">Meleagridinae <span style="font-size:85%;">(turkeys)</span></a></li> <li><a href="/wiki/Perdicinae" title="Perdicinae">Perdicinae</a></li> <li><a href="/wiki/Phasianinae" title="Phasianinae">Phasianinae <span style="font-size:85%;">(pheasants and relatives)</span></a></li> <li><a href="/wiki/Grouse" title="Grouse">Tetraoninae</a></li></ul> </div></td></tr></tbody></table><div></div></td></tr></tbody></table><div></div></td></tr></tbody></table><div></div></td></tr><tr><td colspan="2" class="navbox-list navbox-odd" style="width:100%;padding:0"><div style="padding:0 0.25em"></div><table class="nowraplinks navbox-subgroup" style="border-spacing:0"><tbody><tr><th scope="row" class="navbox-group" style="width:1%"><a href="/wiki/Neoaves" title="Neoaves">Neoaves</a></th><td class="navbox-list-with-group navbox-list navbox-odd" style="width:100%;padding:0"><div style="padding:0 0.25em"></div><table class="nowraplinks navbox-subgroup" style="border-spacing:0"><tbody><tr><th scope="row" class="navbox-group" style="width:1%"><a href="/wiki/Columbea" title="Columbea">Columbea</a></th><td class="navbox-list-with-group navbox-list navbox-odd" style="width:100%;padding:0"><div style="padding:0 0.25em"></div><table class="nowraplinks navbox-subgroup" style="border-spacing:0"><tbody><tr><th scope="row" class="navbox-group" style="width:1%"><a href="/wiki/Columbimorphae" title="Columbimorphae">Columbimorphae</a></th><td class="navbox-list-with-group navbox-list navbox-even" style="width:100%;padding:0"><div style="padding:0 0.25em"> <ul><li><a href="/wiki/Columbidae" title="Columbidae">Columbiformes <span style="font-size:85%;">(doves and pigeons)</span></a></li> <li><a href="/wiki/Mesite" title="Mesite">Mesitornithiformes <span style="font-size:85%;">(mesites)</span></a></li> <li><a href="/wiki/Sandgrouse" title="Sandgrouse">Pterocliformes <span style="font-size:85%;">(sandgrouse)</span></a></li></ul> </div></td></tr><tr><th scope="row" class="navbox-group" style="width:1%"><a href="/wiki/Mirandornithes" title="Mirandornithes">Mirandornithes</a></th><td class="navbox-list-with-group navbox-list navbox-odd" style="width:100%;padding:0"><div style="padding:0 0.25em"> <ul><li><a href="/wiki/Flamingo" title="Flamingo">Phoenicopteriformes <span style="font-size:85%;">(flamingos)</span></a></li> <li><a href="/wiki/Grebe" title="Grebe">Podicipediformes <span style="font-size:85%;">(grebes)</span></a></li></ul> </div></td></tr></tbody></table><div></div></td></tr><tr><th scope="row" class="navbox-group" style="width:1%"><a href="/wiki/Passerea" title="Passerea">Passerea</a></th><td class="navbox-list-with-group navbox-list navbox-odd" style="width:100%;padding:0"><div style="padding:0 0.25em"></div><table class="nowraplinks navbox-subgroup" style="border-spacing:0"><tbody><tr><th scope="row" class="navbox-group" style="width:1%"><a href="/wiki/Otidimorphae" title="Otidimorphae">Otidimorphae</a></th><td class="navbox-list-with-group navbox-list navbox-even" style="width:100%;padding:0"><div style="padding:0 0.25em"> <ul><li><a href="/wiki/Cuckoo" title="Cuckoo">Cuculiformes <span style="font-size:85%;">(cuckoos)</span></a></li> <li><a href="/wiki/Turaco" title="Turaco">Musophagiformes <span style="font-size:85%;">(turacos)</span></a></li> <li><a href="/wiki/Bustard" title="Bustard">Otidiformes <span style="font-size:85%;">(bustards)</span></a></li></ul> </div></td></tr><tr><th scope="row" class="navbox-group" style="width:1%"><a href="/wiki/Strisores" title="Strisores">Strisores</a></th><td class="navbox-list-with-group navbox-list navbox-odd" style="width:100%;padding:0"><div style="padding:0 0.25em"> <ul><li><a href="/wiki/Caprimulgiformes" class="mw-redirect" title="Caprimulgiformes">Caprimulgiformes <span style="font-size:85%;">(nightjars and relatives)</span></a></li> <li><a href="/wiki/Steatornithiformes" class="mw-redirect" title="Steatornithiformes">Steatornithiformes <span style="font-size:85%;">((oilbird))</span></a></li> <li><a href="/wiki/Nyctibiiformes" class="mw-redirect" title="Nyctibiiformes">Nyctibiiformes <span style="font-size:85%;">(Potoos)</span></a></li> <li><a href="/wiki/Podargiformes" class="mw-redirect" title="Podargiformes">Podargiformes <span style="font-size:85%;">(frogmouths)</span></a></li> <li><a href="/wiki/Aegotheliformes" class="mw-redirect" title="Aegotheliformes">Aegotheliformes <span style="font-size:85%;">(owlet-nightjars)</span></a></li> <li><a href="/wiki/Apodiformes" title="Apodiformes">Apodiformes <span style="font-size:85%;">(swifts and hummingbirds)</span></a></li></ul> </div></td></tr><tr><th scope="row" class="navbox-group" style="width:1%"><a href="/wiki/Opisthocomiformes" class="mw-redirect" title="Opisthocomiformes">Opisthocomiformes</a></th><td class="navbox-list-with-group navbox-list navbox-even" style="width:100%;padding:0"><div style="padding:0 0.25em"> <ul><li><a href="/wiki/Opisthocomidae" title="Opisthocomidae">Opisthocomiformes <span style="font-size:85%;">(hoatzin)</span></a></li></ul> </div></td></tr><tr><th scope="row" class="navbox-group" style="width:1%"><a href="/wiki/Cursorimorphae" class="mw-redirect" title="Cursorimorphae">Cursorimorphae</a></th><td class="navbox-list-with-group navbox-list navbox-odd" style="width:100%;padding:0"><div style="padding:0 0.25em"> <ul><li><a href="/wiki/Charadriiformes" title="Charadriiformes">Charadriiformes <span style="font-size:85%;">(gulls and relatives)</span></a></li> <li><a href="/wiki/Gruiformes" title="Gruiformes">Gruiformes <span style="font-size:85%;">(cranes and relatives)</span></a></li></ul> </div></td></tr><tr><th scope="row" class="navbox-group" style="width:1%"><a href="/wiki/Phaethontimorphae" class="mw-redirect" title="Phaethontimorphae">Phaethontimorphae</a></th><td class="navbox-list-with-group navbox-list navbox-even" style="width:100%;padding:0"><div style="padding:0 0.25em"> <ul><li><a href="/wiki/Tropicbird" title="Tropicbird">Phaethontiformes <span style="font-size:85%;">(tropicbirds)</span></a></li> <li><a href="/wiki/Eurypygiformes" title="Eurypygiformes">Eurypygiformes <span style="font-size:85%;">(kagu and sunbittern)</span></a></li></ul> </div></td></tr><tr><th scope="row" class="navbox-group" style="width:1%"><a href="/wiki/Aequornithes" title="Aequornithes">Aequornithes</a></th><td class="navbox-list-with-group navbox-list navbox-odd" style="width:100%;padding:0"><div style="padding:0 0.25em"> <ul><li><a href="/wiki/Loon" title="Loon">Gaviiformes <span style="font-size:85%;">(loons or divers)</span></a></li> <li><a href="/wiki/Penguin" title="Penguin">Sphenisciformes <span style="font-size:85%;">(penguins)</span></a></li> <li><a href="/wiki/Procellariiformes" title="Procellariiformes">Procellariiformes <span style="font-size:85%;">(albatrosses and petrels)</span></a></li> <li><a href="/wiki/Stork" title="Stork">Ciconiiformes <span style="font-size:85%;">(storks)</span></a></li> <li><a href="/wiki/Suliformes" title="Suliformes">Suliformes <span style="font-size:85%;">(cormorants and relatives)</span></a></li> <li><a href="/wiki/Pelecaniformes" title="Pelecaniformes">Pelecaniformes <span style="font-size:85%;">(pelicans and relatives)</span></a></li></ul> </div></td></tr><tr><th scope="row" class="navbox-group" style="width:1%"><a href="/wiki/Australaves" title="Australaves">Australaves</a></th><td class="navbox-list-with-group navbox-list navbox-even" style="width:100%;padding:0"><div style="padding:0 0.25em"> <ul><li><a href="/wiki/Cariamiformes" title="Cariamiformes">Cariamiformes <span style="font-size:85%;">(seriemas and relatives)</span></a></li> <li><a href="/wiki/Falconiformes" title="Falconiformes">Falconiformes <span style="font-size:85%;">(falcons and relatives)</span></a></li> <li><a href="/wiki/Parrot" title="Parrot">Psittaciformes <span style="font-size:85%;">(parrots)</span></a></li> <li><a href="/wiki/Passerine" title="Passerine">Passeriformes <span style="font-size:85%;">(perching birds)</span></a></li></ul> </div></td></tr><tr><th scope="row" class="navbox-group" style="width:1%"><a href="/wiki/Afroaves" title="Afroaves">Afroaves</a></th><td class="navbox-list-with-group navbox-list navbox-odd" style="width:100%;padding:0"><div style="padding:0 0.25em"> <ul><li><a href="/wiki/Accipitriformes" title="Accipitriformes">Accipitriformes <span style="font-size:85%;">(raptors)</span></a></li> <li><a href="/wiki/Owl" title="Owl">Strigiformes <span style="font-size:85%;">(owls)</span></a></li> <li><a href="/wiki/Mousebird" title="Mousebird">Coliiformes <span style="font-size:85%;">(mousebirds)</span></a></li> <li><a href="/wiki/Trogon" title="Trogon">Trogoniformes <span style="font-size:85%;">(trogons and quetzals)</span></a></li> <li><a href="/wiki/Cuckoo-roller" title="Cuckoo-roller">Leptosomiformes <span style="font-size:85%;">(cuckoo-roller)</span></a></li> <li><a href="/wiki/Bucerotiformes" title="Bucerotiformes">Bucerotiformes <span style="font-size:85%;">(hornbills and hoopoes)</span></a></li> <li><a href="/wiki/Coraciiformes" title="Coraciiformes">Coraciiformes <span style="font-size:85%;">(kingfishers and rollers)</span></a></li> <li><a href="/wiki/Piciformes" title="Piciformes">Piciformes <span style="font-size:85%;">(woodpeckers and relatives)</span></a></li></ul> </div></td></tr></tbody></table><div></div></td></tr></tbody></table><div></div></td></tr></tbody></table><div></div></td></tr></tbody></table><div></div></td></tr></tbody></table><div></div></td></tr></tbody></table><div></div></td></tr></tbody></table><div></div></td></tr></tbody></table><div></div></td></tr><tr><td class="navbox-abovebelow" colspan="2"><div> <ul><li><span class="noviewer" typeof="mw:File"><span title="Category"><img alt="" src="//upload.wikimedia.org/wikipedia/en/thumb/9/96/Symbol_category_class.svg/16px-Symbol_category_class.svg.png" decoding="async" width="16" height="16" class="mw-file-element" srcset="//upload.wikimedia.org/wikipedia/en/thumb/9/96/Symbol_category_class.svg/23px-Symbol_category_class.svg.png 1.5x, //upload.wikimedia.org/wikipedia/en/thumb/9/96/Symbol_category_class.svg/31px-Symbol_category_class.svg.png 2x" data-file-width="180" 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