374 



PRACTICAL ZOOLOGY 



so covered with lichens as to resemble its surroundings very 

 closely. Two tiny eggs are laid (Fig. 234). The young are fed 

 by regurgitation. 



The chimney swift breeds commonly in eastern North America. 

 This species formerly made its nest in hollow trees, but now usu- 

 ally frequents chimneys. When in the open air, it is always on 

 the wing, catching insects or gathering twigs from the dead 

 branches of trees for its nest. The twigs are glued together with 



FIG. 256. Vesper sparrow on nest in a field. (Photo, by Hegner.) 



saliva and firmly fastened to the inside of the chimney, forming 

 a cup-shaped nest (Figs. 249, 250, 251). Certain species of 

 Chinese swifts make nests entirely of a secretion from the sal- 

 ivary glands, producing the birds' nests eaten for food in China. 

 PERCHING BIRDS. Over one half of the twelve thousand 

 species of birds belong to this group. They are divided into 

 sixty-four families, twenty-five of which have representatives 

 in this country. It is impossible to give an adequate account of 

 them here because of lack of sp?ce, so the student is urged to 

 refer to books devoted especially to birds. Some of the common 



