166 YEARBOOK 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 TIIEIR 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. 
