﻿FOOD HABITS OF THE VIREOS 25 



ary, when according to our point of view few should be found, 

 they amount to 14.1 per cent. The yearly average, from the data 

 available, is 6.2 per cent. 



Spiders. — ^Except for February, spiders were eaten in all months of 

 the year that are represented by stomachs. The percentage is never 

 high, December with 6.83 being the maximum and June next with 

 4.16 per cent. The average for the eight months is 2.05 per cent. 



VEGETABLE FOOD 



The record of vegetable food for the Hutton vireos is fragmentary, 

 though coinciding so far as it goes with the known habits of other 

 species of this family of birds. Except for months when no vegetable 

 matter was found in the stomachs, the known data show a steady rise 

 in the quantity eaten as the year approaches its end. The December 

 percentage is 7.67 as compared with 0.7 in August. The yearly 

 average is only 1.77 per cent. 



SUMMARY 



The evidence before us, though of questionable value because of 

 the limited quantity of material, points to the fact that the Hutton 

 vireos have a propensity for consuming undue numbers of ladybird 

 beetles and rather fewer caterpillars than other vireos. Final judg- 

 ment should be deferred, however, until additional material is avail- 

 able for analysis. 



THE BELL VIREOS 



Vireo belli, subspp. 



The forms of the Bell vireos, like those of the Hutton, are birds 

 primarily of the western United States, though their range extends 

 much farther east than that of the Hutton vireos. In the willow 

 thickets along water courses birds of this species may be found 

 locally distributed in the greater part of the territory west of the Mis- 

 sissippi River. Although the available material in the collection of 

 the Biological Survey suitable for examination consists of only 52 

 stomachs, these were collected in the months from May to August, 

 inclusive, and serve as a fair index of the summer food. (See fig. 9.) 

 Eleven additional, partially filled stomachs yielded other data con- 

 •ceming food items. Nothing can be said of the winter food at this 

 time. 



ANIMAL FOOD 



Nearly all (99.3 per cent) of the food taken is of animal origin, such 

 forms as bugs, beetles, caterpillars, and grasshoppers predominating. 



Hemiytera. — Bugs make up 34.43 per cent of the summer food of 

 the Bell vireos. Of these about a quarter (9.34 per cent of the total 

 food) - are referable to the family of stink-bugs (Pentatomidae). 

 More stink-bugs are eaten early and late in summer than in July and 

 August. On the other hand, the rest of the hcmipterans show a 

 steady decrease as the season advances. In May more than half the 

 hemiptorous food was made up of bugs other than stink-bugs; June 

 shows a decrease to 28.07 per cent, July to 11.61 per cent, and in 

 August only 4 per cent belongs in this category. 



