166 YEAKBOOK OF THE DEPARTMENT OF AGRICULTURE. 



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 in- 

 terference of man and so rapid is the digestion of birds and so per- 

 fect 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 obtained 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, occasion- 

 ally 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. That the exact nature of the services 

 they render may be better understood, the food habits of certain of 

 the more prominent ones will be briefly reviewed. 



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 spar- 

 row hawk lives largely upon grasshoppers and crickets, and some, 

 even of the larger species, as the Swainson hawk of the Western 

 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 are so very 

 destructive to vegetation that but for the check on their increase 

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

 greater than it is. 



