4 
and birds of other families feeding together in the midst 
of a dense cloud of locusts. 
The study of birds and their habits with regard to (1) 
whether they injure agriculture by eating fruits, grains, 
etc., that the farmer is raising for his own benefit, or 
(2) whether they aid agriculture by eating injurious insects 
and the seeds of undesirable plants or weed, or (3) whether 
they neither help nor hinder by their feeding habits is 
known as economic ornithology. Birds of the first class 
are known as “injurious,” of the second class as “beneficial/’ 
and of the third class as “neutral.” 
The recognition of the part played by birds in the pro¬ 
tection of crops, orchards, and forests has grown with the 
development of economic ornithology and is comparatively 
recent. The earliest information concerning the food of 
most birds was fragmentary or consisted of deductions from 
insufficient data. This led to statements and beliefs some 
of which are now known to be entirely erroneous. For ex¬ 
ample, thirty years ago in the United States hawks and owls 
were almost universally looked upon as injurious to man’s 
interest, and thousands of them were killed each year be¬ 
cause they sometimes ate chickens. There are a very few 
species which live almost exclusively on chickens and 
game birds, but most hawks and owls eat hundreds of field 
mice to each chicken they kill and, therefore, deserve to be 
protected. These facts were determined by the Biological 
Survey of the United States Department of Agriculture from 
a study of the stomach contents of hundreds of birds. Si¬ 
milar results have been obtained in the same way with 
regard to the predacious birds of Europe. 
The Bureau of Biological Survey has done more work 
on economic ornithology than any other single institution. 
Since this line of study was begun in 1885, over sixty 
thousand stomachs have been examined and some of the 
results have been published in more than one hundred 
thirty papers. These deal with such subjects as Birds as 
conservators of the forest, Birds of California in relation 
to the fruit industry, The relations between birds and in¬ 
sects, The hawks and owls of the United States in their 
