488 University of California Publications in Zoology [VOL. 11 



totality of factors governing the food-taking of birds. In other 

 words, in spite of the fact that birds select food to a greater 

 extent than many other animals, they do not select kinds or 

 quantities of food elements to the degree to which we have been 

 led to believe from experiments on captive birds, but are gov- 

 erned more largely by the abundance, the ease of capture, the 

 conspicuousness, etc., of the insect, or, in other words, its avail- 

 ability. 



The attempt has been made heretofore to interpret the food 

 habits of birds from the standpoint of the insect, an endeavor 

 being made to show why certain insects were not taken as food. 

 Looking at the same problem from the standpoint of the bird, 

 we can say that with few exceptions the term availability, when 

 defined as above, best expresses the interrelations associated 

 with the food habits of birds. Under this term can be grouped 

 both the objective factors concerned, such as abundance, ease of 

 capture, conspicuousness, etc., and the psychological factors 

 involved in the taking of food. 



SOLVED AND UNSOLVED PROBLEMS IN ECONOMIC 

 ORNITHOLOGY 



In spite of the advance made in the study of the food of birds 

 and their relation to agriculture, there are still many problems 

 connected with economic ornithology that are still unsolved. 



Great improvement in the technique of determining the food 

 of birds has been achieved. The modern method of stomach 

 examination combined with field observation is so far ahead of 

 the former method of simple observation or inferential reasoning 

 that one is led to believe that a solution of many of the problems 

 presented is near at hand. The criteria used in determining the 

 status of a bird have also been improved to such an extent that 

 were it possible to obtain the prescribed kind of evidence our 

 estimates of the value of a bird must needs be near the truth. 



Our goal, "a balance of all the benefits conferred against all 

 the injuries inflicted," is a fine ideal, but we are still unable to 

 attain it. A great deal is still made of the fact that certain birds 

 eat large quantities of injurious insects. Yet what are injurious 

 insects? Insects injurious in one place may be comparatively 



