462 University of California Publications in Zoology [Vol. 11 



A great number of factors operating together determine the 

 abundance of an insect. Birds and other natural enemies are 

 but one of these many factors. The rate of reproduction and 

 food supply are probably more important factors. In spite of 

 this fact birds are one of the limiting factors and are deserving 

 of attention as such. 



The following facts have been demonstrated by these investi- 

 gations : 



1. Birds cannot be considered a dependable means of com- 

 pletely controlling all insect outbreaks, but can be inferred to be 

 instrumental in the prevention of many. 



2. Birds can be depended upon to act as defenders and pro- 

 tectors of crops because of their warfare against insect pests. 



3. Birds change their food habits and feed on the insect most 

 abundant, thereby making themselves important maintainers of 

 the desired balance in nature. 



4. The failure of birds to check an insect outbreak entirely 

 is evident to all. Their success in preventing insects from be- 

 coming abundant is not so apparent, but is none the less real. 

 All obtainable evidence points to the fact that the regulative 

 influence exerted by birds when insects are to be found in normal 

 numbers, though less apparent, is none the less important, for 

 at such times artificial control measares are seldom used. 



5. Birds, which on account of their abundance cause serious 

 losses to the agriculturist, often become for the same reason the 

 most efficient insect destroyers at the time of an insect outbreak. 



6. Birds help to maintain an equilibrium in nature. Their 

 destruction, therefore, causes a dangerous disturbance of that 

 balance of nature most suited to mankind. 



Verdict of R.\nchers 

 In order that the opinion of the men mo.st directly concerned 

 might not be overlooked, a circular letter was sent out to promi- 

 nent ranchers throughout the state. A copy of the letter follows : 



Deak Sir: — 



The State Fish and Game Commission has taken up the study of the 

 meadowlark in its relation to agriculture and desires to know what you 

 think of the bird. In order to secure comprehensive and uniform data, 

 answers to the following questions are urgently requested: 



