BIRDS AS REGULATORS OF OUTBREAKS. 77 



lard, dusky duck, pintail, and blue-winged teal — contained 

 quantities of 'hoppers. Two out of five white pelicans exam- 

 ined had varied their diet of crayfish and frogs by picking up 

 locusts, one containing forty-one and the other sixty-seven 

 specimens. 



The gulls — including the black-backed, herring, ring-billed, 

 and Franklin's rosy gull — had eaten many grasshoppers, as 

 had also the least and the black tern. 



It certainly would be difficult to obtain more striking evi- 

 dence than this concerning the utility of birds in checking out- 

 breaks of injurious insects. The fact that birds of all sorts 

 and sizes, from the giant pelican to the tiny humming-bird, 

 — birds of the prairie, the forest, the air, the shore, the sea, 

 and the inland lake, — fed so largely upon the locusts proves 

 beyond doubt that these feathered allies were using to the 

 fullest extent a tremendous force to check the ranks of the 

 invaders. 



A few years ago the army-worm appeared in great num- 

 bers in Pennsylvania, causing much damage to field crops. 

 The State zoologist, Professor B. H. Warren, made a careful 

 series of investigations to determine the extent to which birds 

 fed upon the pests. The results showed that a large propor- 

 tion of the common birds devoured them eagerly. Crows, 

 blackbirds, robins, cat-birds, thrushes, meadow-larks, and 

 bluebirds were found to get a large part of their food from 

 the hosts of the army-worms. Kill-deers, sand-pipers, and 

 sparrows also fed freely upon them, while the screech-owl 

 and the sparrow-hawk devoured great numbers of the pests. 



Insects, however, are not the only animals against whose 

 undue increase the agriculturist needs protection. In many 

 parts of Europe there have been for centuries periodic out- 

 breaks of field-mice that have caused enormous injury. The 

 species oftenest concerned appears to be the short-tailed field- 

 mouse (Arvicola agrestis), related to the common meadow- 

 mice of the United States. There is abundant evidence that 



