444 University of California Publications in Zoology [VOL. 11 



Certain species of birds when hungry will not only fill the 

 stomach, but will continue eating until the gullet is also filled. 

 This is often found to be the case with linnets and bicolored 

 blackbirds. In no case, however, has the gullet of a western 

 meadowlark been found well filled with food. At the most, the 

 last insect taken before the bird was collected has been found in 

 the lower part of the gullet. 



CAPACITY FOR GOOD OR EVIL AS EVIDENCED BY THE NUMBER OF 

 BIRDS TAKING THE DIFFERENT ITEMS OF FOOD 



The percentage-volume method of estimating the proportion 

 of the different kinds of food taken by a bird gives us the best 

 idea of the relative importance of the different kinds of food 

 in the diet of a given bird. However, the frequency of occur- 

 rence of the different items in the food, shown by a statement 

 of the number of birds taking each item, furnishes additional 

 evidence as to the capacity of a species for good or ill. The 

 number of birds taking a certain kind of insect food can be 

 regarded as an approximate index of the availability of that 

 kind of food, and to a much less extent as an index of food 

 preference if we consider insects as being evenly distributed and 

 birds as being but slightly influenced by psychological processes. 

 A nearer approximation can be obtained by multiplying the 

 number of birds by the number of insects taken. In such a 

 computation the number of insects taken is considered, as well 

 as the number of birds taking the different elements of food. 

 By this method the index of availability of crickets at Live Oak, 

 Sutter County, was four in 1911, whereas this index was 6902 

 at Hollister, San Benito County, in the same year. By the same 

 method of calculation the index of availability of grasshoppers 

 was 2162 at Live Oak and but 1541 at Hollister. In the first 

 case crickets were 1670 times as available at Hollister as at 

 Live Oak, and grasshoppers 1.4 times more available at Live Oak 

 than at Hollister. The following table gives a comparison of 

 availability of the commoner insects as evidenced by indices of 

 availability. Preference is here classed as a factor in availability. 



