40 USEFUL BIRDS. 
save by such checks as may come, in time, through natural 
causes. 
In view of the dangers threatened by insect increase and 
voracity, how fortunate it is for the human race that so many 
counter-checks are provided against the multiplication of 
these destructive creatures. If we could increase by so much 
as one per cent. the efficiency of the natural enemies of 
insects, a large proportion of the loss occasioned by insect 
injury might be saved. Hence the importance of the study 
of these natural enemies, among which birds hold a high 
place. 
THE CAPACITY OF BIRDS FOR DESTROYING PESTS. 
When we realize the losses that insects are capable of in- 
flicting, we see at once that birds, in their capacity of insect 
destroyers, continually operate to prevent the destruction of 
some of our most important industries. If birds are present 
in sufficient numbers, they will prevent the excessive increase 
of any kind of a pest which they will eat. 
The number of birds required to accomplish this highly 
desirable end need not be very large in comparison with the 
number of insects; for each bird can devour an incredible 
number of insects, and the young birds in the nests require 
more of this food, in proportion to their size, than do their 
parents. 
The Digestion of Birds. 
The digestive organs of birds are so constructed and 
equipped that they can both contain and dispose of a very 
large quantity of food. The stomachs of many species 
quickly separate the indigestible portions of the food from 
the digestible parts, and the former are thrown out of the 
mouth, thus relieving the stomach of much worthless mate- 
rial, and enabling the bird immediately to consume more 
food. The alimentary canal (including the crop, gullet or 
cesophagus, the first division of the stomach or proventricu- 
lus, the gizzard, gigerium or second division of the stomach, 
the intestine and the cloaca) consists of a tube reaching from 
mouth to anus, conveying the food. The nutritious qualities 
of the food are drawn off by the lacteals as it passes; the 
