80 BIRDS IX THEIR RELATIONS TO MAN. 



numbers, and before long they are in myriads. Inconceivable 

 numbers of birds are doubtless in these regions continually 

 passing over us unseen." 



In the presence of an unusual abundance of food the rate 

 of increase of some birds becomes greater. It has been noticed 

 that owls multiply rapidly when outbreaks of mice occur. 



Testimony of this kind could be multiplied indefinitely : it 

 unquestionably is sufficient to demonstrate that when an out- 

 break of mice or similar pests occurs the hawks and owls find 

 an abundant food supply, of which they readily avail them- 

 selves, and in so doing check to a great extent the damage 

 that might be done. 



The evidence furnished by these examples suffices to show 

 that birds do exert a decided influence in checking unusual 

 outbreaks of injurious animals. They have been well likened 

 to a great standing army which may be concentrated at short 

 notice upon any locality where an outbreak occurs. 



V 



CHIl'l'lXG-SI'AKUOW AT N KST. 



