View source for Biology:Bird feet and legs

{{Short description|Hindlimbs primarily used for the anchoring and locomotion of avians}}
[[File:African Jacana (Actophilornis africanus).jpg|thumb|upright=1.35|[[Biology:African jacana|African jacana]]. Extremely long toes<ref name="Gill01" /> and claws help distribute the jacana's weight over a wide area to allow it to walk on floating leaves.<ref name="Kochan94" />]]
{{Main|Biology:Bird anatomy}}
The anatomy of '''bird legs and feet''' is diverse, encompassing many accommodations to perform a wide variety of functions.<ref name="Gill01" />

Most birds are classified as [[Biology:Digitigrade|digitigrade]] animals, meaning they walk on their toes rather than the entire foot.<ref name=kochan-proctor-sibleybeh /><ref name="Dict90_1" /> Some of the lower bones of the foot (the [[Biology:Carpus and tarsus of land vertebrates|distals]] and most of the metatarsal) are fused to form the [[Biology:Tarsometatarsus|tarsometatarsus]] – a third segment of the leg, specific to birds.<ref name=proctor-dict-dobrowolski /><ref name="Romer77" /> The upper bones of the foot ([[Biology:Carpus and tarsus of land vertebrates|proximals]]), in turn, are fused with the [[Biology:Tibia|tibia]] to form the [[Biology:Tibiotarsus|tibiotarsus]], as over time the [[Biology:Carpus and tarsus of land vertebrates|centralia]] disappeared.<ref name="Proctor93" /><ref name="Romer77" /><ref name="Dict90_1" /><ref name="Dobrowolski81" /> The [[Biology:Fibula|fibula]] also reduced.<ref name=proctor-dict-dobrowolski>{{harvp|Proctor |Lynch|1993}}; {{harvp|Kowalska-Dyrcz|1990}}; {{harvp|Dobrowolski et al|1981}}</ref>

The legs are attached to a strong assembly consisting of the [[Biology:Pelvis|pelvic girdle]] extensively fused with the uniform spinal bone (also specific to birds) called the ''[[Biology:Synsacrum|synsacrum]]'', built from some of the fused bones.<ref name="Dobrowolski81" /><ref name="Dict90_2" />
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[[File:Bird leg and pelvic girdle skeleton EN.gif|thumb|upright=1.35|Bird left leg and pelvic girdle skeleton]]

== Hindlimbs ==
Birds are generally [[Biology:Digitigrade|digitigrade]] animals (toe-walkers),<ref name="Proctor93" /><ref name="SibleyBeh01" /> which affects the structure of their leg skeleton. They use only their [[Biology:Hindlimb|hindlimb]]s to walk ([[Bipedalism|bipedalism]]).<ref name="Kochan94" /> Their forelimbs evolved to become [[Physics:Wing|wing]]s. Most bones of the avian foot (excluding toes) are fused together or with other bones, having changed their function over time.

=== Tarsometatarsus ===
Some lower bones of the foot are fused to form the [[Biology:Tarsometatarsus|tarsometatarsus]] – a third segment of the leg specific to birds.<ref name="Dobrowolski81" /> It consists of merged [[Biology:Carpus and tarsus of land vertebrates|distals]] and metatarsals II, III and IV.<ref name="Romer77" /> Metatarsus I remains separated as a base of the first toe.<ref name="Dict90_1" /> The tarsometatarsus is the extended foot area, which gives the leg extra lever length.<ref name="Proctor93" />

=== Tibiotarsus ===
The foot's upper bones ([[Biology:Carpus and tarsus of land vertebrates|proximals]]) are fused with the [[Biology:Tibia|tibia]] to form the [[Biology:Tibiotarsus|tibiotarsus]], while the [[Biology:Carpus and tarsus of land vertebrates|centralia]] are absent.<ref name=proctor-dict-dobrowolski /><ref name="Romer77" /> The anterior (frontal) side of the dorsal end of the tibiotarsus (at the knee) contains a protruding enlargement called the [[Biology:Cnemial crest|cnemial crest]].<ref name="Kochan94" />

=== Patella ===
At the knee above the [[Biology:Cnemial crest|cnemial crest]] is the [[Biology:Patella|patella]] (kneecap).<ref name="Dict90_1" /> Some species do not have patellas, sometimes only a  cnemial crest. In grebes both a normal patella and an extension of the cnemial crest are found.<ref name="Kochan94" />

=== Fibula ===
The [[Biology:Fibula|fibula]] is reduced and adheres extensively to the tibia, usually reaching two-thirds of its length.<ref name="Kochan94" /><ref name="Proctor93" /><ref name="Dobrowolski81" /> Only penguins have full-length fibulae.<ref name="Dict90_1" />

=== Knee and ankle – confusions ===
[[File:Pelargopsis_chick.jpg|thumb|left|Chick of ''Pelargopsis capensis'' with heel-pads]]
The bird knee joint between the [[Biology:Femur|femur]] and [[Biology:Tibia|tibia]] (or rather [[Biology:Tibiotarsus|tibiotarsus]]) points forwards, but is hidden within the feathers. The backward-pointing "heel" (ankle) that is easily visible is a joint between the [[Biology:Tibiotarsus|tibiotarsus]] and [[Biology:Tarsometatarsus|tarsometatarsus]].<ref name=kochan-proctor-sibleybeh /><ref name="Dict90_1" /> The joint inside the tarsus occurs also in some reptiles. It is worth noting here that the name "thick knee" of the members of the family [[Biology:Stone-curlew|Burhinidae]] is a misnomer because their heels are large.<ref name="Kochan94" /><ref name="Dobrowolski81" /> 

The chicks in the orders [[Biology:Coraciiformes|Coraciiformes]] and [[Biology:Piciformes|Piciformes]] have ankles covered by a patch of tough skins with tubercles known as the ''heel-pad''. They use the heel-pad to shuffle inside the nest cavities or holes.<ref>{{Cite journal | last=Munn | first=Philip W. | date=1 January 1894 | title=On the Birds of the Calcutta District | journal=Ibis | volume=36 | issue=1 | pages=39–77 | doi=10.1111/j.1474-919x.1894.tb01250.x | issn=1474-919X}}</ref><ref>{{Cite journal | last=Chasen | first=F. N. | year=1923 | title=On The Heel-Pad in certain Malaysian Birds | journal=Journal of the Malayan Branch of the Royal Asiatic Society | volume=1 | issue=87 | pages=237–246 | jstor=41559544 | jstor-access=free}}</ref>

=== Toes and unfused metatarsals ===
[[File:Straußenfuß.jpg|thumb|upright=1.0|The ostrich is the only bird that has the didactyl foot.<ref name="Kochan94" />]]
Most birds have four toes, typically three facing forward and one pointing backward.<ref name="Proctor93" /><ref name="SibleyBeh01" /><ref name="Dobrowolski81" /> In a typical perching bird, they consist respectively of 3, 4, 5 and 2 phalanges.<ref name="Kochan94" /> Some birds, like the [[Biology:Sanderling|sanderling]], have only the forward-facing toes; these are called tridactyl feet while the [[Biology:Ostrich|ostrich]] have only two toes (didactyl feet).<ref name="Kochan94" /><ref name="Dict90_1" /> The first digit, called the hallux, is [[Biology:Homology|homologous]] to the human big toe.<ref name="Proctor93" /><ref name="SibleyBeh01" />

The [[Biology:Claw|claw]]s are located on the extreme phalanx of each toe.<ref name="Dict90_1" /> They consist of a horny [[Biology:Keratin|keratin]]ous [[Biology:Podotheca|podotheca]], or sheath,<ref name="Kochan94" /> and are not part of the skeleton.

The bird foot also contains one or two metatarsals not fused in the [[Biology:Tarsometatarsus|tarsometatarsus]].<ref name="Dobrowolski81" />

== Pelvic girdle and synsacrum ==
The legs are attached to a very strong, lightweight assembly consisting of the [[Biology:Pelvis|pelvic girdle]] extensively fused with the uniform spinal bone called the [[Biology:Synsacrum|synsacrum]],<ref name="Proctor93" /><ref name="SibleyBeh01" /> which is specific to birds. The synsacrum is built from the [[Biology:Vertebral column|lumbar]] fused with the [[Biology:Vertebral column|sacral]], some of the first sections of the [[Biology:Vertebral column|caudal]], and sometimes the last one or two sections of the [[Biology:Vertebral column|thoracic]] vertebrae, depending on species (birds have altogether between 10 and 22 vertebrae).<ref name="Dict90_2" /> Except for those of [[Biology:Ostrich|ostrich]]es and [[Biology:Rhea (bird)|rheas]], pubic bones do not connect to each other, easing [[Biology:Egg|egg]]-laying.<ref name="Dobrowolski81" />

== Rigidity and reduction of mass ==
Fusions of individual bones into strong, rigid structures are characteristic.<ref name="Gill01" /><ref name="Proctor93" /><ref name="SibleyBeh01" />

Most major bird bones are extensively pneumatized. They contain many air pockets connected to the pulmonary [[Medicine:Lung#Avian lungs|air sacs]] of the [[Biology:Bird anatomy#Respiratory system|respiratory system]].<ref name="Wedel03" /> Their spongy interior makes them strong relative to their mass.<ref name="Kochan94" /><ref name="Proctor93" /> The number of pneumatic bones depends on the species; pneumaticity is slight or absent in [[Biology:Diving bird|diving bird]]s.<ref name="Schorger47" /> For example, in the [[Biology:Long-tailed duck|long-tailed duck]], the leg and wing bones are not pneumatic, in contrast with some of the other bones, while [[Biology:Loon|loon]]s and [[Biology:Puffin|puffin]]s have even more massive skeletons with no aired bones.<ref name="Fastovsky05" /><ref name="Gier52" />  The flightless [[Biology:Ostrich|ostrich]] and [[Biology:Emu|emu]] have pneumatic [[Biology:Femur|femur]]s, and so far this is the only known pneumatic bone in these birds<ref name="Bezuidenhout99" /> except for the ostrich's cervical vertebrae.<ref name="Wedel03" />

Fusions (leading to rigidity) and pneumatic bones (leading to reduced mass) are some of the many adaptations of birds for flight.<ref name="Gill01" /><ref name="Proctor93" />

== Plantigrade locomotion ==
Most birds, except [[Biology:Loon|loon]]s and [[Biology:Grebe|grebe]]s, are [[Biology:Digitigrade|digitigrade]], not [[Biology:Plantigrade|plantigrade]].<ref name="Kochan94" /> Also, [[Biology:Bird|chicks]] in the nest can use the entire [[Biology:Foot|foot]] (toes and [[Biology:Tarsometatarsus|tarsometatarsus]]) with the heel on the ground.<ref name="Dict90_1" />

Loons tend to walk this way because their legs and [[Biology:Pelvis|pelvis]] are highly specialized for swimming. They have a narrow pelvis, which moves the attachment point of the [[Biology:Femur|femur]] to the rear, and their [[Biology:Tibiotarsus|tibiotarsus]] is much longer than the femur. This shifts the feet (toes) behind the [[Physics:Center of mass|center of mass]] of the loon body. They walk usually by pushing themselves on their breasts; larger loons cannot take off from land.<ref name="SibleyBeh01" /> This position, however, is highly suitable for swimming because their feet are located at the rear like the [[Engineering:Propeller|propeller]] on a [[Engineering:Motorboat|motorboat]].<ref name="Kochan94" />

[[Biology:Grebe|Grebe]]s and many other waterfowl have shorter [[Biology:Femur|femur]] and a more or less narrow pelvis, too, which gives the impression that their legs are attached to the rear as in [[Biology:Loon|loon]]s.<ref name="Kochan94" />

==Functions==
[[File:Psittacus erithacus erithacus -feet on perch-8a.jpg|thumb|upright=1.0|[[Biology:Grey parrot|Grey parrot]] grips the perch with zygodactyl feet.]]
[[File:Füße eines Chile-Flamingo Zoo Landau.JPG|thumb|upright=1.0|Palmate feet – [[Biology:Chilean flamingo|Chilean flamingo]].]]
[[File:Blue-footed Booby (Sula nebouxii) -feet.jpg|thumb|upright=1.0|Totipalmate feet – blue-footed booby.]]
[[File:Aechmophorus occidentalis foot.jpg|thumb|upright=1.0|[[Biology:Western grebe|Western grebe]] presenting a lobate foot.]]
[[File:Eurasian-Coot--chick.jpg|thumb|upright=1.0|Lobate feet – a chick of the Eurasian coot.]]
[[File:Podiceps cristatus - Holzbrücke 2011-06-14 17-12-54.JPG|thumb|upright=1.0|The [[Biology:Great crested grebe|great crested grebe]]. The feet in loons<ref name="Kochan94" /> and grebes<ref name="Kochan94" /><ref name="Proctor93" /> are placed far at the rear of the body - a powerful accommodation to swimming underwater,<ref name="Proctor93" /> but a handicap for walking.]] 
[[File:Lagopus lagopus foot.jpg|thumb|upright=1.0|The [[Engineering:Snowshoe|snowshoe]]-like foot of the willow ptarmigan is an adaptation for walking on snow.<ref name="Gill01" />]]
Because avian forelimbs are wings, many forelimb functions are performed by the bill and [[Biology:Hindlimb|hindlimb]]s.<ref name="SibleyBeh01" /> It has been proposed that the hindlimbs are important in flight as accelerators when taking-off.<ref name="Earls00" /><ref name="Whitfield00" /> Some leg and foot functions, including conventional ones and those specific to birds, are:
* Locomotion
** Walking, running ([[Biology:Ostrich|ostrich]]es, [[Biology:Grouse|grouse]], [[Biology:Wild turkey|wild turkey]]s) hopping, climbing ([[Biology:Woodpecker|woodpecker]]s, [[Biology:Nuthatch|nuthatch]]es, [[Biology:Treecreeper|treecreeper]]s)<ref name=gill-kochan-proctor-sibleybeh />
** Swimming and steering underwater ([[Biology:Duck|duck]]s, [[Biology:Grebe|grebe]]s, [[Biology:Loon|loon]]s)<ref name=kochan-proctor-sibleybeh />
* Perching (as on a branch) or clinging<ref name=kochan-proctor-sibleybeh />
* Carrying (like [[Biology:Osprey|osprey]]s holding [[Biology:Fish|fish]])<ref name=kochan-proctor-sibleybeh />
* Flight-related
** Serving probably as the primary take-off accelerator. In the [[Biology:Common vampire bat|common vampire bat]], by contrast, the required force is generated by the [[Biology:Bat#Wings and flight|wing]].<ref name="Earls00" /><ref name="Whitfield00" />
** Absorbing the shock of landing on a perch and on the water, becoming "water skis"<ref name=kochan-proctor-sibleybeh />
* Feeding and related
** Catching and killing prey in raptors ([[Biology:Hawk|hawk]]s, [[Biology:Owl|owl]]s)<ref name=kochan-proctor-sibleybeh />
** Holding (used like hands in [[Biology:Parrot|parrot]]s) and pulling apart food (with help from the bill)<ref name=kochan-proctor-sibleybeh />
** Scratching the ground in search of food<ref name="Kochan94" />
*** Double scratch: hopping forward and then backward using both feet to scratch (often [[Biology:Towhee|towhee]]s, [[Biology:Old World sparrow|sparrow]]s, [[Biology:Junco|junco]]s)<ref name="Kochan94" />
*** One-footed scratch ([[Biology:Grouse|grouse]], [[Biology:Quail|quail]]s, [[Biology:Wild turkey|wild turkey]]s, [[Biology:Chicken|domestic chicken]])<ref name="Kochan94" />
*Reproduction and related
** Cradling and turning [[Biology:Egg|egg]]s during incubation.<ref name=kochan-proctor-sibleybeh /> Birds lacking a [[Biology:Brood patch|brood patch]] incubate the eggs with their feet – grasping one or even two of them (gannets, boobies) or keeping them on the top surfaces of their feet ([[Biology:Penguin|penguin]]s under a pouch of belly skin, [[Biology:Uria|murres]]).<ref name="Gill01" />
** Courtship (sage grouse), including aerial courtship ([[Biology:Bald eagle|bald eagle]]s)<ref name=kochan-proctor-sibleybeh />
** Building nests (with help from the bill)<ref name="Gill01" />
* Preening and cleaning.<ref name="SibleyBeh01" /> Sometimes birds use a special [[Biology:Claw|claw]] (for example, [[Biology:Barn owl|barn owl]]s have a so-called "feather comb"). Some [[Biology:Heron|heron]]s and nightjars use the claw for cleaning the head.<ref name="Kochan94" />
* Heat loss regulation ([[Biology:Heron|heron]]s, [[Biology:Gull|gull]]s, [[Biology:Giant petrel|giant petrel]]s, [[Biology:Stork|stork]]s, [[Biology:New World vulture|New World vulture]]s, [[Biology:Duck|duck]]s, [[Biology:Goose|geese]])<ref name="Gill01" /><ref name="Kochan94" />

==Toe arrangements==
[[File:Bird feet - toe arrangement (dactyly) EN.gif|thumb|upright=2|none|Toe arrangement in a bird's right foot]]
Typical toe arrangements in [[Biology:Bird|bird]]s are:
* '''Anisodactyl''': three toes in front (2, 3, 4), and one in back (1); in nearly all [[Biology:Songbird|songbird]]s and most other perching birds.<!--, swifts from the subfamilies ''Cypseloidinae'' and ''Chaeturinae''<ref name="SibleyBeh01" />--><ref name="Dict90_1" /><ref name=gill-kochan-proctor-sibleybeh>{{harvp| Gill | 2001}}; {{harvp| Kochan | 1994}}; {{harvp| Proctor |Lynch| 1993}}; {{harvp| Elphick et al| 2001}}</ref>
* '''Zygodactyl''': two toes in front (2, 3) and two in back (1, 4) – the outermost front toe (4) is reversed. The zygodactyl arrangement is a case of [[Biology:Convergent evolution|convergence]], because it evolved in birds in different ways nine times.<ref name="Gill01" /><ref name="SibleyBeh01" />
** In many perching birds – most [[Biology:Woodpecker|woodpecker]]s and their allies, [[Biology:Osprey|osprey]]s, [[Biology:Owl|owl]]s, [[Biology:Cuckoo|cuckoo]]s, most [[Biology:Parrot|parrot]]s, [[Biology:Mousebird|mousebird]]s, some [[Biology:Swift (bird)|swift]]s and [[Biology:Cuckoo roller|cuckoo roller]]s.<ref name=gill-kochan-proctor-sibleybeh /><ref name="Dict90_1" />
*** Woodpeckers, when climbing, can rotate the outer rear digit (4) to the side in an ectropodactyl arrangement. [[Biology:Black-backed woodpecker|Black-backed woodpecker]]s, [[Biology:Eurasian three-toed woodpecker|Eurasian three-toed woodpecker]]s and [[Biology:American three-toed woodpecker|American three-toed woodpecker]]s have three toes – the inner rear (1) is missing and the outer rear (4) points always backward and never rotates.<ref name="SibleyBeh01" />
*** [[Biology:Owl|Owl]]s, [[Biology:Osprey|osprey]]s and [[Biology:Turaco|turaco]]s can rotate the outer toe (4) back and forth.<ref name="SibleyBeh01" />
* '''Heterodactyl''': two toes in front (3, 4) and two in back (2, 1) – the inner front toe (2) is reversed; heterodactyl arrangement only exists in [[Biology:Trogon|trogon]]s.<ref name=gill-kochan-proctor-sibleybeh />
* '''Syndactyl''': three toes in front (2, 3, 4), one in back (1); the inner and middle (2, 3) are joined for much of their length.<ref name="Kochan94" /><ref name="Gill01" /> Common in [[Biology:Coraciiformes|Coraciiformes]], including [[Biology:Kingfisher|kingfisher]]s and [[Biology:Hornbill|hornbill]]s.<ref name="Proctor93" />
* '''Pamprodactyl''': two inner toes in front (2, 3), the two outer (1, 4) can rotate freely forward and backward. In [[Biology:Mousebird|mousebird]]s and some [[Biology:Swift (bird)|swift]]s. Some [[Biology:Swift (bird)|swift]]s<!--(''Apodinae''<ref name="SibleyBeh01" />)--> move all four digits forward to use them as hooks to hang.<ref name=gill-kochan-proctor-sibleybeh />

The most common arrangement is the anisodactyl foot, and second among perching birds is the zygodactyl arrangement.<ref name=kochan-proctor-sibleybeh /><ref name="Proctor93" /><ref name="Kalbe83" />

==Claws==
All birds have claws at the end of the toes. The claws are typically curved and the radius of curvature tends to be greater as the bird is larger although they tend to be straighter in large ground dwelling birds such as ratites.<ref>{{cite journal|doi=10.1017/S0952836903004382|title=Scaling of bird claws|journal=Journal of Zoology|volume=262|pages=73–81|year=2004|last1=Pike|first1=A. V. L.|last2=Maitland|first2=D. P.}}</ref> Some species (including [[Biology:Nightjar|nightjar]]s, [[Biology:Heron|heron]]s, [[Biology:Frigatebird|frigatebird]]s, owls and [[Biology:Pratincole|pratincole]]s) have comb-like serrations on the claw of the middle toe that may aid in scratch preening.<ref name = "Stettenheim">{{Cite journal |last=Stettenheim |first=Peter R.|date=August 2000|title=The Integumentary Morphology of Modern Birds—An Overview|journal=American Zoologist|volume=40|issue=4|pages=461–477|doi=10.1668/0003-1569(2000)040[0461:timomb]2.0.co;2 |issn=0003-1569|citeseerx=10.1.1.559.1172}}</ref>

== {{anchor|lobed feet}} Webbing and lobation ==
[[File:Bird feet - webbing and lobation EN.gif|thumb|upright=2|none|Webbing and lobation in a bird's right foot]]
Palmations and lobes enable swimming or help walking on loose ground such as [[Earth:Mud|mud]].<ref name=kochan-proctor-sibleybeh /> The webbed or palmated feet of birds can be categorized into several types:
* '''Palmate''': only the anterior digits (2–4) are joined by webbing. Found in [[Biology:Duck|duck]]s, [[Biology:Goose|geese]] and [[Biology:Swan|swan]]s, [[Biology:Gull|gull]]s and [[Biology:Tern|tern]]s, and other aquatic birds ([[Biology:Auk|auk]]s, [[Biology:Flamingo|flamingo]]s, [[Biology:Fulmar|fulmar]]s, jaegers, [[Biology:Loon|loon]]s, [[Biology:Petrel|petrel]]s, [[Biology:Shearwater|shearwater]]s and skimmers).<ref name=gill-kochan-proctor-sibleybeh /><ref name="Kalbe83" /> [[Biology:Diving duck|Diving duck]]s also have a lobed hind toe (1), and gulls, terns and allies have a reduced hind toe.<ref name=kochan-sibleybeh>{{harvp| Kochan | 1994}}; {{harvp| Elphick et al| 2001}}</ref>
* '''Totipalmate''': all four digits (1–4) are joined by webbing. Found in gannets and boobies, [[Biology:Pelican|pelican]]s, [[Biology:Cormorant|cormorant]]s, [[Biology:Anhinga|anhinga]]s and [[Biology:Frigatebird|frigatebird]]s. Some gannets have brightly colored feet used in display.<ref name=kochan-proctor-sibleybeh /><ref name="Kalbe83" />
* '''Semipalmate''': a small web between the anterior digits (2–4). Found in some [[Biology:Plover|plover]]s ([[Biology:Eurasian dotterel|Eurasian dotterel]]s) and [[Biology:Sandpiper|sandpiper]]s ([[Biology:Semipalmated sandpiper|semipalmated sandpiper]]s, [[Biology:Stilt sandpiper|stilt sandpiper]]s, [[Biology:Upland sandpiper|upland sandpiper]]s, [[Biology:Greater yellowlegs|greater yellowlegs]] and [[Biology:Willet|willet]]), [[Biology:Avocet|avocet]], [[Biology:Heron|heron]]s (only two toes), all [[Biology:Grouse|grouse]], and some domesticated breeds of [[Biology:Chicken|chicken]]. Plovers and [[Biology:Lapwing|lapwing]]s have a vestigial hind toe (1), and sandpipers and their allies have a reduced and raised hind toe barely touching the ground. The [[Biology:Sanderling|sanderling]] is the only sandpiper having 3 toes (tridactyl foot).<ref name=kochan-proctor-sibleybeh>{{harvp| Kochan | 1994}}; {{harvp| Proctor |Lynch| 1993}}; {{harvp| Elphick et al| 2001}}</ref>
* '''Lobate''': the anterior digits (2–4) are edged with lobes of skin. Lobes expand or contract when a bird swims. In [[Biology:Grebe|grebe]]s, [[Biology:Coot|coot]]s, [[Biology:Phalarope|phalarope]]s, [[Biology:Heliornithidae|finfoots]] and some palmate-footed [[Biology:Duck|duck]]s on the hallux (1). Grebes have more webbing between the toes than coots and phalaropes.<ref name=gill-kochan-proctor-sibleybeh /><ref name="Dict90_1" /><ref name="Kalbe83" />
The palmate foot is most common.

==Thermal regulation==
Some birds like [[Biology:Gull|gull]]s, [[Biology:Heron|heron]]s, [[Biology:Duck|duck]]s or [[Biology:Goose|geese]] can regulate their temperature through their feet.<ref name="Gill01" /><ref name="Kochan94" />

The [[Biology:Artery|arteries]] and [[Medicine:Vein|vein]]s intertwine in the legs, so heat can be transferred from arteries back to veins before reaching the feet. Such a mechanism is called [[Physics:Countercurrent exchange|countercurrent exchange]]. [[Biology:Gull|Gull]]s can open a shunt between these vessels, turning back the bloodstream above the foot, and constrict the vessels in the foot. This reduces heat loss by more than 90 percent. In gulls, the temperature of the base of the leg is 32&nbsp;°C (89&nbsp;°F), while that of the foot may be close to 0&nbsp;°C (32&nbsp;°F).<ref name="Gill01" />

However, for cooling, this heat-exchange network can be bypassed and blood-flow through the foot significantly increased ([[Biology:Giant petrel|giant petrel]]s). Some birds also excrete onto their feet, increasing heat loss via [[Physics:Evaporation|evaporation]] ([[Biology:Stork|stork]]s, [[Biology:New World vulture|New World vulture]]s).<ref name="Gill01" />

==See also==
* [[Biology:Bird anatomy|Bird anatomy]]
* [[Biology:Dactyly|Dactyly]]
* [[Biology:Synsacrum|Synsacrum]]
* [[Biology:Tarsometatarsus|Tarsometatarsus]]
* [[Biology:Tibiotarsus|Tibiotarsus]]

==References==
{{Commons}}
{{Reflist|2|refs=

<ref name="Bezuidenhout99">{{cite journal | last1=Bezuidenhout | first1=A.J. | last2=Groenewald | first2=H.B. | last3=Soley | first3=J.T. | year=1999 | title=An anatomical study of the respiratory air sacs in ostriches | journal=Onderstepoort Journal of Veterinary Research | volume=66 | issue=4 | pages=317–325 | url=http://repository.up.ac.za/bitstream/handle/2263/20155/39bezuidenhout1999.pdf | pmid=10689704 }}</ref>

<ref name="Dict90_1">{{cite book |last=Kowalska-Dyrcz |first=Alina |editor-last=Busse |editor-first=Przemysław |series=Mały słownik zoologiczny <nowiki>[</nowiki>Small zoological dictionary<nowiki>]</nowiki> |title=Ptaki |language=Polish |trans-title=Birds |pages=383–385 |chapter=Entry: noga <nowiki>[</nowiki>leg<nowiki>]</nowiki> |edition=1st |volume=I |publisher=Wiedza Powszechna |location=Warsaw |year=1990 |isbn=978-83-214-0563-6}}</ref>

<ref name="Dict90_2">{{cite book |ref=none |last=Kowalska-Dyrcz |first=Alina |editor-last=Busse |editor-first=Przemysław |series=Mały słownik zoologiczny <nowiki>[</nowiki>Small zoological dictionary<nowiki>]</nowiki> |title=Ptaki |language=Polish |trans-title=Birds |page=245 |chapter=Entry: synsakrum <nowiki>[</nowiki>synsacrum<nowiki>]</nowiki> |edition=1st |volume=II |publisher=Wiedza Powszechna |location=Warsaw |year=1990 |isbn=978-83-214-0563-6}}</ref>

<ref name="Dobrowolski81">{{cite book | last1=Dobrowolski | first1=Kazimierz A. | last2=Klimaszewski | first2=Sędzimir M. | last3=Szelęgiewicz | first3=Henryk | publisher=Wydawnictwo Szkolne i Pedagogiczne | location=Warsaw | year=1981 | pages= 462–464, 469 | chapter=Chapters: Gromada: Ptaki - Aves: Układ kostny; Pas miednicowy i kończyna tylna <nowiki>[</nowiki>Class: Birds: The skeletal system; The pelvic girdle and the hindlimb<nowiki>]</nowiki> | title=Zoologia | edition=4th | language=Polish | trans-title=Zoology | isbn=978-83-02-00608-1|ref={{harvid|Dobrowolski et al|1981}} }}</ref>

<ref name="Earls00">{{cite journal | last=Earls | first=Kathleen D. | date=Feb 2000 | title=Kinematics and mechanics of ground take-off in the starling Sturnis vulgaris and the quail ''Coturnix coturnix'' | journal=The Journal of Experimental Biology | volume=203 | issue=Pt 4 | pages=725–739 | doi=10.1242/jeb.203.4.725 | url=http://jeb.biologists.org/content/jexbio/203/4/725.full.pdf | pmid=10648214 }}</ref>

<ref name="Fastovsky05">{{cite book | last1=Fastovsky | first1=David E. | last2=Weishampel | first2=David B. | publisher=Cambridge University Press | location=Cambridge, UK | year=2005 | title=The Evolution and Extinction of the Dinosaurs | edition=2nd | url=https://books.google.com/books?id=M8nt10bkovIC&pg=PA304| isbn=978-0-521-81172-9 }}</ref>

<ref name="Gier52">{{cite journal |last=Gier |first=H. T. | year=1952 |title=The air sacs of the loon |journal=The Auk | volume=69 | issue = 1 | pages=40–49 | url=https://sora.unm.edu/sites/default/files/journals/auk/v069n01/p0040-p0049.pdf | doi=10.2307/4081291|jstor=4081291 }}</ref>

<ref name="Gill01">{{cite book | last=Gill | first=Frank B. | publisher=W.H. Freeman and Company | location=New York | year=2001 | title=Ornithology | edition=2md | isbn=978-0-7167-2415-5 }}</ref>

<ref name="Kalbe83">{{cite book | last=Kalbe | first=Lothar | publisher=Urania-Verlag | location=Leipzig-Jena-Berlin | year=1983 | pages= 72–77 | chapter=Besondere Formen für spezielle Aufgaben der Wassertiere <nowiki>[</nowiki>Special adaptations of aquatic animals to specific lifestyles<nowiki>]</nowiki> | title=Tierwelt am Wasser | edition=1st | language=German | trans-title=Wildlife by the Water }}</ref>

<ref name="Kochan94">{{cite book | last=Kochan | first=Jack B. | series=Birds | title=Feet & Legs | publisher=Stackpole Books | location=Mechanicsburg | year=1994 | isbn=978-0-8117-2515-6}}</ref>

<ref name="Proctor93">{{cite book |last1=Proctor |first1=Noble S. |last2=Lynch |first2=Patrick J. |title=Manual of Ornithology. Avian Structure & Function |publisher=Yale University Press | location=New Haven and London | year=1993 | pages=70–75, 140–141, 142–144 | chapter=Chapters: 6. Topography of the foot, 11. The pelvic girdle, and 12. The bones of the leg and foot Family | isbn=978-0-300-07619-6 }}</ref>

<ref name="Romer77">{{cite book | last1=Romer | first1=Alfred Sherwood |  last2=Parsons | first2=Thomas S. |  year=1977 | title=The Vertebrate Body | publisher=Holt-Saunders International | location= Philadelphia, PA | pages= 205–208 | isbn= 978-0-03-910284-5 }}</ref>

<ref name="Schorger47">{{cite journal | last=Schorger | first=A. W. | date=September 1947 | title=The deep diving of the loon and old-squaw and its mechanism | journal=The Wilson Bulletin | volume=59 | issue=3 | pages=151–159 | url=https://sora.unm.edu/sites/default/files/journals/wilson/v059n03/p0151-p0159.pdf }}</ref>

<ref name="SibleyBeh01">{{cite book | last1=Elphick | first1=John B. | last2=Dunning | first2=Jack B.  Jr.| last3=Sibley | first3=David Allen | title=National Audubon Society: The Sibley Guide to Bird Life & Behavior | publisher=Alfred A. Knopf | location=New York | year=2001 | isbn=978-0-679-45123-5 | ref={{harvid|Elphick et al|2001}} | url-access=registration | url=https://archive.org/details/sibleyguidetobir00sibl_1 }}</ref>

<ref name="Wedel03">{{cite journal | last=Wedel | first=Mathew J. | year=2003 | title=Vertebral pneumaticity, air sacs, and the physiology of sauropod dinosaurs | journal=Paleobiology | volume=29 | issue=2 | pages=243–255 | url=http://sauroposeidon.files.wordpress.com/2010/04/wedel-2003-sauropod-pneumaticity.pdf | doi=10.1666/0094-8373(2003)029<0243:vpasat>2.0.co;2}}</ref>

<ref name="Whitfield00">{{Cite journal | url=http://www.nature.com/news/2000/000310/full/news000316-1.html | title=Off to a flying jump-start : Nature News | journal=Nature | last=Whitfield | first=John | date=10 March 2000 | publisher=Nature Publishing Group | accessdate=17 January 2014 | doi=10.1038/news000316-1 }}</ref>

}}

[[Category:Bird anatomy]]

{{Sourceattribution|Bird feet and legs}}