FOOD HABITS OF THE VIKEOS 19 
ANIMAL FOOD 
Animal matter (96.32 per cent) in the food of birds of this species 
is, as usual in this family, composed almost 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-thro at ; 
but ; even so, the quantity consumed is of academic rather than, 
economic interest. 
Lepidoptera. — The blue-headed vireos eat almost as many cater- 
pillars during the year as does the yellow- thro at, 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 in 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. 
Eemiptera. — 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 consumption 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-throat. 
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. 
