10 USEFUL BIBDS. 



when insect food is not plentiful, and so be ready to check 

 any increase of insects which may occur. On the other 

 hand, if they become too numerous, they may create serious 

 disturbances by destroying grass, grain, or fruit. I have 

 witnessed attacks made by certain of these beetles on grain 

 and strawberries ; and were they not held in check by 

 birds, it is probable that they would soon become serious 

 pests. Their destruction by Robins and other birds tends 

 to keep these beetles within those normal bounds where 

 they will do most good and least harm ; while the check 

 kept by the Crow on the increase of the Robin may pre- 

 vent the latter from destroying too many ground beetles. 

 If certain low-feeding caterpillars became so numerous as to 

 be injurious, ground beetles and Robins would feed largely 

 on them. The caterpillars would then largely take the place 

 of the beetles in the Robin's food. The beetles, therefore, 

 would increase in numbers, and the force of both bird and 

 beetle would be exerted to reduce the caterpillars to their 

 normal limit. This accomplished, the Robin would again 

 attack the ground beetles, and thus tend to reduce them 

 to normal numbers. 



Let us now go back to the beginning of our chain of 

 destruction. The Eagles, Hawks, Owls, and raccoons may 

 indirectly allow an increase in the number of Robins by 

 preventing too great an increase of the Crow. But Hawks 

 and Owls also prey on the Robin, and, by dividing their 

 attention between Robin and Crow, assist in keeping both 

 birds to their normal numbers. Whenever Crows became 

 rare, Robins as a consequence would become very numerous, 

 were it not that the Hawks also eat Robins. (Hawks and 

 Owls eat also some species of insects that are eaten by both 

 Robin and Crow.) 



There are compensations in the apparently destructive 

 career of the Crow. An omnivorous bird, it seems inclined 

 to turn its attention to any food which is plentiful and readily 

 obtained. It is a great feeder on May beetles (miscalled 

 "June bugs"), the larvas of which, known as white grubs, 

 burrowing in the ground, sometimes devastate grass lands 

 and also injure the roots of many plants, including trees. 



