﻿FOOD HABITS OF THE VIEEOS 19 



ANIMAL FOOD 



Animal matter (96.32 per cent) in the food of birds of this species 

 is, as usual in this family, composed ahnost entirely of insects, the few 

 spiders eaten forming but 2.63 per cent and the snails 0.25 per cent, 

 respectively, of the whole. This represents a slightly greater prefer- 

 ence for each of these items than that displayed by the yellow-throat;. 

 but, even so, the quantity consumed is of academic rather than, 

 economic interest. 



Lepidoptera. — The blue-headed vireos eat almost as many catei-- 

 pillars during the year as does the yellow-throat, but their record for 

 chrysalids and adults is not so favorable. The consumption of 

 caterpillars increases rapidly during January, February, and March, 

 when they constitute 41.56 per cent of the food of that season, and 

 then drops to 10.47 per cent in May, and rises again to 40.39 per cent 

 in September, after which it decreases rapidly with the approach of 

 winter. This fluctuation is marked and, as it does not coincide with 

 the known life cycle of the insects, may be attributed to fluctuating 

 abundance of other more palatable or attractive foods. The average 

 of the monthly percentages is found to be slightly below that for the 

 yellow- throated vireo, being 22.49 per cent. On the other hand, the 

 consumption of adult moths commenced in February with the 

 relatively high percentage of 20.32 and steadily dwindled to 7.26 per 

 cent iu May. A rise, culminating in July with a percentage of 18.38, 

 was immediately followed by a drop to 2.22 per cent in August. 

 From August until the end of the season, the adult lepidopterans 

 were taken in steadily increasing quantity, closing in November at 

 5.1. The yearly average of this item is 9.31 per cent, less than half 

 that of the yellow-throat. Lepidopterans in all stages contribute 31.8 

 per cent of the entire annual subsistence. 



Hemiptera. — True bugs form the second largest item of food of the 

 blue-headed vireos. Owing to the predominance of stink-bugs 

 (Pentatomidae) over all other kinds, this family has been tabulated 

 separately. During the winter months hibernating pentatomids 

 constitute one of the most important sources of food for the blue- 

 headed vireos, as shown by the November and January percentages of 

 48.7 and 29.02, respectively. During February, March, April, and 

 May there is considerable fluctuation in the quantities eaten, but all 

 these months have relatively high percentages, the highest being 

 29.6 in April. June and July apparently offer more attractive food 

 along other lines, as the consmnption of stink-bugs then drops to 3.45 

 and 4.38 per cent, respectively. August shows a sudden increase to 

 16.4 per cent, and from then on the item assumes considerable 

 importance. The yearly average (20.13 per cent) is considerably 

 more than that of the yellow-tlnoat. 



The other bugs make up only about half as much of the total bulk 

 of the food as do the pentatomids, but it is interesting to note that the 

 ratio between these forms and the rest of the bugs is almost identical 

 in both species of Lanivireo. There appears to be no rule followed 

 by the blue-heads in their selection of bugs other than pentatomids 

 for food, but in general they eat few before June and a great many in 

 the later months of the year. March is an exceptional month, in 

 that 12.91 per cent represents the miscellaneous bugs taken. 



