354 



AVES 



The swallows {Fam. Hirundinidae) are extremely efficient insect 

 destroyers. Their relatives, the purple martins^ will readily take 

 up their abode in bird houses. The mocking-birds, thrashers and 

 wrens are beautiful singers and important enemies of insects. The 

 warblers {Fajn. Mniotilitidae) include over one hundred species, 

 about seventy-five of which are found in the United States. They 

 are important enemies of insects. 



Fig. 198. Whitebreasted nuthatch. (Courtesy of F. E. Brooks.) 



The Anatomy and Physiology of Birds 



No animal has feathers except the bird. " A bird is known by 

 its feathers." Every part of the organization is modified for aerial 

 life. 



Characteristics. — i. Feathers. 



1. Sternum and shoulder girdle enlarged to support wing mus- 

 cles. 



3. Forelimbs modified as wings. 



