The Dazzling Diversity of Avian Feet I I Text Lisa Nupen Anisodactyl
BIOLOGY insight into the birds’ different modes of life. THE BONES IN THE TOES Birds’ feet are not only used for n almost all birds, the number of bones locomotion (walking or running, Iin each toe is preserved: there are two swimming, climbing), but they bones in the first toe (digit I), three bones serve other important functions in in the second toe (II), four in the third (III) perching, foraging, preening, re- and five in the fourth (IV). Therefore, the production and thermoregulation. identity of a toe (I to IV) can be determined Because of this, the structure of a quite reliably from the number of bones in bird’s foot often provides insight it. When evolutionary toe-loss occurs, this into the species’ ecology. Often, makes it possible to identify which digit distantly related species have con- has been lost. verged on similar foot types when adapting to particular environ- ments. For example, the four fully demands of a particular niche or The first, and seemingly ances- webbed, forward-pointing toes environment. The arrangement tral, configuration of birds’ toes – called totipalmate – of pelicans, of toes in lovebirds, barbets and – called anisodactyly – has three gannets and cormorants are an ad- cuckoos, for example, is differ- digits (numbered II, III and IV) aptation to their marine habitat. ent from that in passerines (such orientated forwards and digit I The closely related Shoebill as finches, shrikes or starlings) in (the ‘big toe’, or hallux) pointing does not have webbed feet, per- the same environment. The func- backwards. This arrangement is haps because of its wetland habi- tional reasons for differences in shared with theropod fossils and The toes of penguins tat, but the tropicbirds, which foot structure can be difficult to is the most common, being found (below left) and gan- fancy form their own relatively ancient explain.
[Show full text]