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 14 birds, 

 various unidentified insect pupse 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 4 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. 35). In 

 addition, 18 percent was composed of pupae 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 pupse likewise were consumed. 



One brood of the second group, Avhich 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 



