460 SCIENCE OF HOME AND COMMUNITY 



beneficial or injurious. In order to do this, specimens of 

 birds are collected in different months and from different 

 states. The experts at Washington open the stomachs of 

 these birds and make a careful study of their contents. 

 From this study they are able to determine what food the 

 birds have been eating. So far the Bureau of Biological 

 Survey has examined more than sixty thousand stomachs, 

 comprising over four hundred species of birds. 



For instance, in order to find out about the food of the 

 robin, 1236 specimens were collected in different months 

 from forty-two states, the District of Columbia, and three 

 Canadian Provinces. It was found that about one seventh 

 of the robin's food was made up of things valuable to man, 

 such as fruit and beneficial insects, one third was composed 

 of injurious insects, and about one half was made of neutral 

 elements, chiefly wild fruit. 



Birds as insect destroyers. These studies have shown 

 that insects form the chief food of birds, and that most of 

 these insects are injurious to man because they feed upon 

 the crops he is raising, or because they carry diseases. Birds 

 help man because they keep these insects down to such a 

 point that man is able to control those that remain. If man 

 were to be deprived of the services of the birds, insects would 

 increase to such an extent that man would have a terrible 

 struggle to overcome them. 



Amount eaten by birds. One thing that makes birds so 

 helpful is the fact that they devour so many insects in the 

 course of a day. Birds watched in the field have been ob- 

 served to eat from two to ninety insects in a minute, depend- 

 ing on the bird and the kind of insect. In the studies made 

 by the Biological Survey it was found that a single stomach 

 of a bird contained a great many insects. For instance, the 

 stomach of a grosbeak was found to contain fourteen potato 

 beetles ; a crow blackbird, thirty grasshoppers ; and a flicker, 

 five thousand ants. 



