450 



COLLEGE ZOOLOGY 



in shifts; and with a few birds, such as some 

 ostriches and shore birds, the male performs 

 practically all of this duty. 



Two general classes of young are recog- 

 nized: (1) those that are able to run about 

 soon after hatching, as young chickens do, 

 are known as precocial birds (Fig. 320); 

 and (2) those that remain in the nest for a 

 greater or lesser period before they are able 

 to take care of themselves are known as 

 altricial birds. 



OTHER BIRDS 



Wingless and flightless birds 



Five orders of living birds are flightless. 

 These include ostriches, rheas, cassowaries, 

 emus, penguins, and kiwis. Ostriches (Fig. 

 305) are the largest living birds, attain- 

 ing a height of more than 8 feet and a 

 weight of over 300 pounds. Although flight- 



less, they can run at a speed of more than 

 50 miles per hour. They live in dry open 

 regions of Africa and travel about in groups, 

 but do not stick their heads in the sand and 

 think themselves hidden, as commonly re- 

 ported. The nest is a hollow in the sand, 

 and several females lay their eggs in a single 

 nest. The males uncover and incubate the 

 eggs at night and cover them with warm 

 sand by day. 



Rheas (Fig. 322) are New World os- 

 triches which inhabit the pampas of South 

 America. They are smaller than the true 

 ostriches, but their habits are quite similar. 

 Cassowaries (Fig. 305) and emus are ostrich- 

 like birds; the emus (Fig. 321) are confined 

 to Australia, and the cassowaries, the world's 

 third largest flightless bird, to New Guinea 

 and neighboring islands. Kiwis (Fig. 305) 

 are wingless birds that live in New Zealand. 

 They are about the size of a common fowl; 

 their wings are rudimentary, and they lack 



Figure 321. An adult emu with chicks. The young emu is strikingly striped, a characteristic 

 which disappears as the flightless bird becomes mature. (Courtesy of Victorian Railways.) 



