614 



COLLEGE ZOOLOGY 





salivary glands, producing the edible birds'-nests of the 

 Chinese. 



The woodpeckers (Picid^e), comprising about three hundred 

 and fifty species, are found in wooded regions almost everywhere 

 except in the Australian region and Madagascar. About fifty 

 species occur in North America. The downy, hairy, and red- 

 headed woodpeckers, the nicker, and the yellow-bellied sap- 

 sucker are the best known. Woodpeckers use their chisel-shaped 



bills for excavating holes 

 in trees, at the bottom of 

 which their eggs are laid, 

 or for digging out grubs 

 from beneath the bark. 

 Most of them are of great 

 benefit because of the 

 insects they destroy, but 

 the yellow-bellied sap- 

 sucker (Fig. 503) is harm- 

 ful, since it eats the cam- 

 bium of trees and sucks 

 sap. 



Order 21. Passeri- 

 formes. — Sparrow-like 

 Birds (Fig. 504). — It is 

 necessary, because of lack 

 of space, to refer the 

 student to books on birds for a detailed account of the birds 

 included in this order. On page 591 will be found a list of 

 the principal families. Almost half, about seven thousand 

 species and subspecies, of all the birds known belong to this 

 order. They are grouped into sixty-four families ; rep- 

 resentatives belonging to twenty- five of these occur in North 

 America. 



Passerine birds are usually small or of medium size, but are 

 the most highly organized of the .class Aves. Their feet are 



Fig. 503. — Yellow-bellied sapsucker, Sphy- 

 rapicus varins. (From Judd, Bui. 17, Bur. 

 Biol. Survey, U. S. Dep't Agric.) 



