74 FOOD HABITS OF THE GROSBEAKS., 
The remaining constituents of the animal food have slight per- 
centage value. Fifteen grosbeaks devoured spiders or their cocoons, 
these items amounting to 0.34 percent of the entire regimen. Among 
other substances of little importance are snails, eaten by 1+ birds, 
various unidentified insect pupe by 10, eggshells by 5, and flies by 
2; and, most remarkable for a bird of the blackhead’s feeding habits, 
a bit of bone and the remains of a small fish were found in a single 
stomach each. 
MINERAL MATTER. 
The average percentage of mineral matter in the stomachs of the 
whole number of birds examined is 2.35. The nestlings of 2 or 3 
days’ age had none; those of a week, 6.57 percent; and those of 2 
weeks, only 3 in number, however, had 2.33 percent. 
NESTLINGS. 
We are fortunate in having a fair amount of material to illustrate 
the food habits of the nestling black-headed grosbeaks. The nestlings 
at hand are readily divisible into three groups, separated both by age 
and character of the diet. Ten, comprising two broods of 3 each and 
one of 4+, which were collected at the age of 2 and 3 days, had been 
fed animal matter exclusively. Seven, made up of two broods, num- 
bering 3 and + individuals, respectively, had reached the age of 7 and 
8 days, at which period a small amount, namely, 2.1 percent, of vege- 
table food had been introduced into the dietary, while 3 scattered 
fledgelings of a fortnight’s growth consumed an average of 13.3 per- 
cent of vegetable substances, mainly fruit. 
Two-thirds of the food of the youngest or entirely insectivorous 
group consisted of caterpillars, much over half of which, to wit, 37.2 
percent, was spring cankerworms (Paleacrita vernata, fig. 85). In 
addition, 18 percent was composed of pupe of the codling moth (fig. 
34), which, indeed, were fed to part or all of each brood, including 8 
of the 10 nestlings. If the habit of feeding these important pests, 
on the scale here indicated, to nestlings, whose never-ceasing demands 
for food are proverbial, is general, the amount of destruction wrought 
in their ranks is almost incalculable. Besides the codling moth and 
cankerworm, the flower-beetle and black olive scale also figure in the 
diet of this lot of youngsters; and longicorn beetles, spiders, leaf- 
hoppers, other bugs, and ant pup likewise were consumed. 
One brood of the second group, which was just being initiated into 
the use of vegetable food, was given oats in the milk, while the other 
family was entirely carnivorous. More hard-bodied insects are fed 
