258 



VERTEBRATA 



That birds limit in a large degree the outbreaks of injuri- 

 ous animals is shown by recent reports. An apple orchard 

 in Illinois was severely attacked by canker worms (Fig. 88) 

 and numerous species of birds came to feed on the pests. 

 Several individuals of each of thirty-six different species 

 were killed and the stomach contents examined by Pro- 



FiG. 295. A, Screech owl. Photograph from life. One fifth natural size. 

 M, Long-eared owl. 



fessor Forbes. Canker worms made up twenty per cent of 

 the food of the robins, fifteen per cent of the food of cat- 

 birds, two thirds of the food of the warblers, forty per 

 cent of the food of the vireos, fifty-nine per cent of the 

 food of the indigo bunting, sixty-one per cent of the food 

 of the chickadees, seventy-five per cent of the food of the 

 black-billed cuckoos, and practically all of the food of 

 the cedar birds. 



