BIRDS AS RELATED TO AGRICULTURE 195 



Among the seed-eating birds are sparrows, finches, gros- 

 beaks, towhees, meadowlarks, and quail. 



Birds as destroyers of insects. One reason birds are able 

 to destroy enormous numbers of insects is due to their ability 

 to get quickly to places where insects are numerous. It 

 may be noticed that an outbreak of grasshoppers is likely to 

 be followed by an increase of birds in that locality. After the 

 grasshoppers have been destroyed the birds pass on to some 

 other place where insect food is more abundant. In this way 

 insects are often kept in check and prevented from doing 

 much damage. 



The number of insects that a single adult bird will eat 

 at one meal is very great, as the following examples will 

 show. A yellow-billed cuckoo is known to have eaten 250 

 tent caterpillars; a nighthawk, 500 mosquitoes; another, 

 320 grasshoppers; a cedar waxwing, 200 canker worms; and 

 a flicker, 28 large grubs. A scarlet tanager was found to 

 have eaten 630 gypsy moth caterpillars in 18 minutes, and 

 a warbler 3500 plant lice in 40 minutes. Among the birds 

 that are largely insect eaters are the warblers, threshers, orioles, 

 flycatchers, swallows, woodpeckers, thrushes, nuthatches, 

 wrens, kinglets, vireos, creepers, titmice, and chickadees. 



Birds as destroyers of rodents and other mammals. Field 

 mice, deer mice, rats, weasels, rabbits, and some other mam- 

 mals are often very destructive of farm plants and farm 

 products. With the exception of the rabbit whose numbers 

 are usually kept down by hunters, the number of these harmful 

 mammals is controlled largely by hawks and owls, and to a 

 certain extent by crows. 



The service rendered by many kinds of hawks and owls is 

 not sufficiently understood and appreciated. Only two com- 

 mon species of hawks, Cooper's hawk and the sharp-shinned 



