THE NATURAL ENEMIES OF BIRDS 131 



Feathered enemies. There is strong evidence 

 that the crow, blue jay, and crow blackbird at 

 times do much damage, especially the crow, in de- 

 stroying eggs and the young of small birds. These 

 birds have been repeatedly observed to attack the 

 nests of other birds, and some students consider 

 the crow the worst natural enemy of small birds. 



An examination of eleven hundred stomachs of 

 crows, made by the Bureau of Biological Survey, 

 showed that fifty, or about five per cent, had fed 

 on wild birds or their eggs. In the same bulletin is 

 the following reference to the egg-eating habit of 

 the blue jay: " As this trait of the jay appears to be 

 most pronounced during its own breeding season, it 

 is quite possible for many birds which have suffered 

 from his boldness early in the season to raise an- 

 other brood unmolested." This egg-destroying 

 habit is probably not true of all crows and jays, 

 but is limited to a certain number of individuals. 



Among the hawks are found some of the worst 

 natural enemies of birds, the chief offenders being 

 the pigeon hawk, Cooper's hawk, and sharp-shinned 

 hawk. They attack the adult birds, and our small 

 insectivorous birds make up over half of the food 

 of the sharp-shinned hawk. 



The owls occasionally feed on small birds, but 

 not nearly so frequently as hawks. They are not to 

 be considered serious enemies of the small birds. 

 Shrikes feed to some extent on small birds, which 



