2 University of California Puilications in Zoology [Vol. 11 



of birds collected each month of the year in ovei- twenty differ- 

 ent parts of the State, are furnishing positive data as to the 

 food of these birds throughout the year. The feeding habits 

 of birds at the time of an insect outbreak, such as that of the 

 differential grasshopper {Melanoplus differ entiaUs) which oc- 

 curred in the San Joaquin Valley in the summer of 1912, afford 

 critical evidence of the value of birds as insect destroyers, and of 

 their part in maintaining that balance in nature most suited to 

 the interests of man. 



It is impossible, however, to determine accurately the full 

 value of birds, for we cannot ftnd out what the result would be 

 upon the insect population, if all the birds were suddenly de- 

 stroyed. Yet a knowledge of their food leads us to conjecture 

 that the destruction of so important an enemy of insects as the 

 birds would result in a great increase in these enemies of vegeta- 

 tion and thus cause a serious disturbance in the balance of nature. 

 The fact that birds destroy large numbers of injurious insects 

 shows them to be important agents in contributing to the safety 

 not onl.y of crops, but also of all vegetation. A realization of 

 the usefulness of birds promotes needed interest in and protec- 

 tion for them. 



It is hoped that, as a result of this investigation and others 

 in progress, the insectivorous habits of many of the common 

 birds, and their consequent value, may be more generally known 

 and appreciated b.y those who most profit by their activities ; and 

 also that this study of the relation of birds to a particular out- 

 break may add something of permanent value to the too meager 

 knowledge of the part played by birds in maintaining the desired 

 balance in nature. 



In the investigation here described an attempt was made to 

 answer the following questions : 



1. What species of birds in California feed on grasshoppers 

 during the periodical outbreaks of these insects ? 



2. To what extent does each species at such times feed on 

 grasshoppers as compared with other food? 



3. How many, and what proportion, of gra.sshoppei"s are 

 destroyed by birds at the time of an outbreak. 



