220 THE ANIMALS AND MAN 



in bringing food for the young, and in defending them from 

 enemies. The young, when ready to hatch, break the egg- 

 shell with the "egg-tooth," a horny pointed projection on 

 the upper mandible, and emerge either blind and almost 

 naked, dependent upon the parents for food until able to 

 fly (altricial young), or with eyes open and with body cov- 



FlG. lis. Western chipping sparrow, Spizella socialis arizonae. (Photo- 

 graph from life by Eliz. and Jos. Grinnell.) 



ered with down, and able in a few hours to feed themselves 

 (precocial young). 



Classification and identification. — The class of birds, 

 Aves, is divided into various orders, of which seventeen are 

 represented in North America. There are eight hundred 

 (approximately) different species of North American birds, 

 but in any one locality not more than about a third of these 

 species can be found, and of these only comparatively few 

 are common or numerous. So that to learn the common 

 birds of a single locality is not a large matter; it means 



