OTHER ANIMALS 631 



the tree tops for such of the enemy as have escaped pursuit below. 

 Thus each family plays its part in the never-ending warfare, and the 

 number of insects annually consumed by the combined hoste is 

 simply incalculable. It is well that this is so, for so vast is the num- 

 ber of insects and so great is the quantity of vegetation required for 

 their subsistence that the existence of every green thing would be 

 threatened were it not for birds and other agents specially designed 

 to keep them in check. 



While birds are not numerous in the sense that insects are, they 

 exist in fair numbers everywhere or would were it not for the inter- 

 ference of man and so rapid is the digestion of birds and so perfect 

 their assimilative powers that, to satisfy the appetite of even a small 

 bird, great numbers of insects are needed. Much of this food is 

 hidden and must be searched for; much of it is active and must be 

 vigorously pursued. Hence only by the expenditure of much time 

 and labor do birds procure their daily food. With birds the struggle 

 for existence is peculiarly a struggle for subsistence; shelter is ob- 

 tained with comparative ease, and if climatic conditions are not to 

 their liking they migrate to other regions. 



When by reason of favorable conditions insects have multiplied 

 and become unusually abundant, birds eat much more than at ordi- 

 nary times ; hence the importance of their services during insect in- 

 vasions. It is not, however, at such periods that their services are 

 most valuable. It is their persistent activity in destroying insects 

 every day, at all seasons, and in every stage of growth the long, 

 steady pull rather than the spasmodic effort that tends to prevent 

 insect irruptions and to keep the balance true. 



Few birds are wholly beneficial, and there are very few among 

 the harmful ones that have no redeeming traits that do not, Occa- 

 sionally at least, do good. Most birds most of the time are beneficial; 

 a few birds most of the time are injurious. Certain species may be 

 beneficial in one region and harmful in others, or perform useful 

 services at one season and be injurious at another. Instead, there- 

 fore, of being simple, as at first sight they may appear, the relations 

 of birds to man are complex. 



INSECTIVOROUS BIRDS AND THEIR FOOD HABITS. 



Hawks and Owls. The strong beaks and sharp talons of the 

 hawks and owls at first sight might be thought designed for more 

 serious work than the destruction of insects, and yet many of the 

 birds of prey make insects an important part of their food. The 

 little sparrow hawk lives largely upon grasshoppers and crickets, and 

 some, even of the larger species, as the Swainson hawk of the West- 

 ern States, in summer time live almost exclusively upon them. It is 

 very fortunate that so many birds the hawks among them are 

 fond of grasshoppers, since these insects multiply so fast and aro so 

 very destructive to vegetation that but for the check on their in- 

 crease by birds the cost to the farmer of fighting them would be 

 much greater than it is. 



Important as is the work of some of the hawks in destroying 

 noxious insects, this is by no means the chief service the group ren- 



