66 BIRD FRIENDS 



that a single bob-wliite will eat in a year an average 

 of 75,000 insects and 5,000,000 weed seeds, which 

 would make about 7^ pounds of insects and 10 

 pounds of weed seeds. 



Examination of stomachs. But the most impor- 

 tant method of determining the food of birds is 

 by examination of the contents of birds' stomachs. 

 This is the final court of appeal, and is the method 

 used chiefly by the Bureau of Biological Survey. 

 Many specimens of a certain bird are collected dur- 

 ing different months from different sections of the 

 country and sent to Washington, where the stomachs 

 are examined. There usually remain in the stomach 

 some of the harder portions of the insects which have 

 not been changed, such as mandibles, scales of 

 moths, wing-covers, and pieces of legs. From an 

 examination of these with microscopes, experts are 

 able to determine the insects from which they have 

 come. Among the vegetable foods, differences in the 

 epidermis of many fruits and in the starch grains of 

 common cereals can be detected, and weed seeds can 

 be identified. Food of similar kinds is arranged in 

 piles and the percentage of the various kinds of food 

 computed. As an illustration of the method pur- 

 sued, we may take results obtained from the study 

 of the robin. Twelve hundred and thirty-six stom- 

 achs, collected from forty-two States, the District 

 of Columbia, and three Canadian Provinces, and 

 representing every month in the year, were exam- 



