292 ANNUAL REPORT SMITHSONIAN INSTITUTION, 1952 



adults. Included in the Passeres are the finches and sparrows and 

 their relatives, forming the largest and most highly specialized group. 

 The sparrows and finches, like the other perching birds, feed their 

 young on insects but as adults are vegetarians, mainly seed eaters. 

 This is the reverse of the conditions seen in most amphibians which 

 are alga and detritus feeders when young, insectivorous as adults. 

 Other perching birds as adults are vegetarian, omnivorous, or insecti- 

 vorous. As seeds are to be found everywhere at all seasons the spar- 

 rows and their relatives are the most generally and widely distributed 

 of all terrestrial birds. They are able to exist under the most severe 

 conditions if sufficient food and water in usable form is available, and 

 therefore are not so strongly migratory as most other birds. 



All sea birds are carnivorous, feeding on crustaceans, fish, and 

 squid. The gulls are mainly scavengers; some feed more or less ex- 

 tensively on large insects, especially grasshoppers and cicadas. 

 Shore birds feed on crustaceans, insects, and small fish, some at cer- 

 tain seasons eating berries. Most of the smaller land birds feed 

 wholly or mainly on insects. All the very large birds, the ostriches, 

 rheas, emus, and cassowaries, are vegetarian, as are the parrots, pi- 

 geons, swans, geese, and many ducks, as well as a number of species 

 in other groups. Gallinaceous birds are chiefly vegetarian, though 

 most of them eat insects, especially when young. Vultures eat carrion, 

 and some birds, like the ravens and crows, are omnivorous. Preda- 

 tory birds feed chiefly on mammals, fish, reptiles, and other birds. 

 Many birds, as woodpeckers and hummingbirds, have highly special- 

 ized feeding habits, and others, like the hoatzin, will eat only a certain 

 kind of food. Very few birds store food, and these only casually. 

 Birds are much more likely to gather shiny, brightly colored, or other- 

 wise attractive objects, a habit shared with certain rodents. 



All birds are completely, or almost completely, feathered, with the 

 legs scaled. The beak suggests that of the turtles. Some, as the vul- 

 tures and a number of gallinaceous and struthious birds, have the 

 head and neck naked. The skin is dry. 



All birds have two pairs of limbs of which the posterior pair is al- 

 ways well developed, at least in the young, adapted for perching, 

 clinging, climbing, running, swimming, or grasping prey, with usually 

 four, sometimes only three or two, clawed digits, three or all four of 

 which may be connected by a web. The anterior pair is usually modi- 

 fied to form wings which in most birds serve for aerial transport, 

 though in individual species in many different groups they are reduced 

 in size and useless for flight, and in such birds as ostriches, rheas, emus, 

 cassowaries, and kiwis, which have greatly enlarged and powerful 

 legs like kangaroos, leaping rodents, and frogs, they are very greatly 

 reduced, especially in the three last. In the penguins the anterior 



