92 BIRD FRIENDS 



do much harm. They eat all sorts of plant prod- 

 ucts, including grains and vegetables. The softer 

 products constitute their summer food, and in the 

 winter, bark and twigs are eaten, damage being 

 done by girdling fruit-trees. In the West they are 

 especially destructive to melons, pears, and cab- 

 bages. 



Pocket gophers live on a great variety of plant 

 products and are especially destructive to potatoes 

 and alfalfa, and do much damage to fruit and shade 

 trees. 



Value of hawks and owls. Nature's chief checks 

 for controlling these rodent pests are the hawks and 

 owls, whose food consists largely of these injurious 

 animals, although insects, poultry, and wild birds 

 form minor items of their food. These two groups 

 of birds supplement each other, the hawks working 

 by day and the owls by night. As with other birds, 

 so here, enormous quantities of food are eaten. It is 

 the habit of owls to disgorge pellets of indigestible 

 matter — bones, fur, etc. — taken with their food. 

 An examination, made by Dr. A. K. Fisher, of the 

 pellets found during a summer beneath the nest of 

 a pair of barn owls showed the presence of 432 skulls 

 of mice and rats, out of a total of 454 skulls found 

 in 200 pellets. A similar study of long-eared owls 

 in another locality, made during several winter 

 months, showed that each owl on the average de- 

 stroyed two mice a day. Under the nest of a pair of 



