UTILITY OF BIRDS IX NATURE . 11 



The Crow is also a destroj'or of cutworms. These are 

 the young or larva* of such noctuid moths or " millers " 

 as are commonly seen fluttering from the grass by any one 

 who disturbs them by walking in the 

 fields. Robins also feed largely on 

 cutworms, as well as on the white Fig. 3. — cutworm. 

 grub of the May beetle. When these insects are few in 

 number, a part of the usual food supply of both Robin 

 and Crow is cut otf. This being the case, the hungry 

 Crows are likely to destroy more young 

 Robins and other young birds than 

 usual, in order to make up the supply 

 of animal food for themselves and their 

 ravenous nestlings. In a few 3'ears this 

 Fig. 4.- Noctuid inoth. ^^.^uld decrease perceptibly the number 

 of Robins and other small birds, and would be likely in 

 turn to allow an increase of May beetles and cutworms. 

 As these insects became more plentiful, the Crows would 

 naturally turn again to them, pa3'ing less attention to the 

 young of Rol)ins and other birds for the time, and allowing 

 them to increase once more, until their multi})lication put 

 a check on the insects, when the Crows would of necessity 

 ao-ain raid the Robins, 



The Blue Jay may be taken as another instance of this 

 means of preserving the balance of nature. Hawks and 

 Owls kill Blue Jays, Crows destroy their eggs and young ; 

 thus the Jays are kept in check. .lays are omnivorous 

 feeders. They eat the eggs and young of other birds, par- 

 ticularly those of Warblers, Titmice, and Vireos, — birds 

 which are active caterpillar hunters. But Jays are also 

 extremely efficient caterpillar hunters. Thus the Jays 

 compensate in some measure for their destruction of cat- 

 erpillar-eating birds, ])y themselves destroying the cater- 

 pillars which they unconsciously have allowed to increase 

 in numbers by destroying these birds. Like the Crow, 

 they virtuaUi/ kill the young of the smaller birds, and eat 

 them, that they (the Jays) may eventually have more in- 

 sect food for their own young. When this ol)ject has been 

 attained, the Jaj's may again, perhaps, allow an increase of 



