UTILITY OF BIRDS IN NATURE. 11 



The C^row is also a destroyer of cut worms. These are 

 the young or larvte of such iioctuid moths or "millers" 

 as are eommonly seen fluttering from the grass by any one 

 who disturbs them by walking in the 

 fields. Eobins also feed largely on -fiySa^B^ 

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

 ffrub of the Ma\' beetle. AMien these insects are few in 

 number, a part of the usual food supplj'^ of both Robin 

 and Crow is cut otl'. This lieing the case, the hungry 

 (^rows 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 years this 

 Fig. 4.-No(tui(iiiu.th. ^^.Qiiifi decrease perceptibh^ the number 



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

 turn to allow an increase of ]\Iay beetles and cutworms. 

 As these insects became more })lentiful, the C^rows would 

 naturally turn again to them, paying less attention to the 

 young of Robins and other birds for the time, and allowing 

 them to increase once more, until their nuiltiplication put 

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

 again raid the Robins, 



The Blue Jay may be taken as another instance of this 

 means of })reserving the balance of nature. Hawks and 

 Owls kill Blue Ja^s, Crows destroy their eggs and young ; 

 thus the flays are kept in check, flays are onmivorous 

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

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

 which are active caterpillar hunters. But -Tays are also 

 extremely efficient cater})illar hunters. Thus the flays 

 compensate in some measure for their destruction of cat- 

 erpillar-eating birds, by themselves destroying the cater- 

 pillars which they unconsciously have allowed to increase 

 in numbers by destroying these birds. Like the Crow, 

 they vlrtmOhj kill the young of the smaller birds, and eat 

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

 sect food for their own young. When this object has been 

 attained, the flays may again, ])erhaps;, allow an increase of 



