Structure and function birds -

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Structure and function birds

Birds > Only the Birds

General structure

Birds have adapted to a multitude of situations. For this reason, they occur in a wide diversity of shapes, sizes, and col-ors. Weighing up to 285 lbs (130 kg), and reaching 9 ft (2.75 m), the flightless ostrich is the largest of the living birds. At a mere 0.7 oz (2 g) and around 2.4 in (6 cm), the tiny bee hummingbird is the smallest. Even closely related forms can look very different (adaptive radiation).A famous example is the enormous range of bill shapes and sizes in Charles Dar-win’s Galápagos finches; a single over-water colonizing species is thought to have undergone repeated evolutionary divergence to produce the 14 or so contemporary species on the different islands. Conversely, unrelated species can closely resemble each other (convergent evolution) because they have evolved for the same lifestyle. Examples of this are the Old World and New World vultures, which belong to the diur-nal birds of prey and storks, respectively.

Body shapes vary enormously, from the flexible, longnecked form of the cranes and ibises to short-necked, stiffbacked falcons and penguins. These latter species, the speedy, predatory hunters of the air and the seas, have torpedo-shaped bodies to minimize drag. Bills and beaks take a variety of forms that generally reflect their major function in feeding: from the sturdy, seed-cracking bills of finches to the long, soil-probing tween species, variation can be quite marked within species, either geographically or between the sexes.

Embryonic development in birds
Embryonic development in birds
Dorsal and ventral views of a birds wing
Dorsal and ventral views of a birds wing

Species often vary in size clinally (with environmental or geographic change), usually increasing in size between from hotter to cooler parts of their range (Bergman’s rule); races at either end of the cline can be remarkably different. A few species even have different forms, for example, the large-and small-beaked snail kites. Males are often larger (sexual dimorphism), but in some species, including birds of prey, some seabirds, and game birds, the female is larger.

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