The Farmer's Feathered Helpers 221 



Flriley and Bohlman 



FIG. 171. A black-throated gray warbler feeding its young. Small birds 

 rear their young almost entirely on insect food. 



The investigations of this bureau have thrown much 

 light upon the problem of the value of birds. Around 

 the nest of a pair of barn owls was found nearly a bushel 

 of the remains of pocket gophers, which are so destructive 

 to the roots of trees and field crops in some parts of the 

 country. In another barn-owl retreat were found three 

 thousand skulls of rats, mice, gophers, and other small 

 animals (Fig. 172). The stomach of a Swainson's hawk 

 contained a hundred grasshoppers, and as birds digest 

 their food very quickly these must all have been eaten 



within a few hours. The lawmakers of Pennsylvania The value 



, , , J , , , e of owls and 



once, in ignorance, placed a bounty on the heads of hawks 



hawks and owls (Figs. 173 and 174). In a year and a half, 

 on account of the increase of field mice and other pests, 

 it was estimated that the state had suffered a loss of 

 four million dollars. The laws now protect these birds 

 of prey, for it has been discovered that, although they 

 may occasionally catch a chicken or a song bird, their 

 food in the main consists of animal pests. 



