BIRDS AS REGULATORS OF OUTBREAKS. 71 



numbers too insignificant to figure in the ratios, the entire 

 food of all these birds consisted of canker-worms, which 

 therefore stand at an average of one hundred per cent. The 

 number in each stomach determined by actual count ranged 

 from seventy to one hundred and one, and was usually nearly 

 one hundred. Assuming that these constituted a whole day's 

 food, the thirty birds were destroying three thousand worms 

 a day, or ninety thousand for the month during which the 

 caterpillar is exposed.'' 



A specimen each of the cliff-swallow, American gold- 

 finch, and yellow- winged sparrow had eaten no canker-worms. 

 About one-third of the food of eight chipping-sparrows con- 

 sisted of caterpillars, half of them being canker-worms. 

 Three field-sparrows had eaten largely of canker-worms and 

 various beetles, forty-three per cent, of the food of fourteen 

 black-throated buntings consisted of canker-worms, and a 

 very few of these worms had been eaten by two rose-breasted 

 grosbeaks ; they also formed fifty-nine per cent, of the food 

 of eighteen indigo-birds. 



No canker-worms were found in the stomachs of a single 

 cow-bird and two red-winged blackbirds. Three Baltimore 

 orioles, however, had eaten forty per cent, of these worms 

 and fifty per cent, of vine-chafers. Two orchard-orioles made 

 even a better showing. " More than three-fourths of the food 

 of these consisted of canker-worms, and other caterpillars 

 made an additional twenty per cent." Three bronzed 

 grackles had eaten no caterpillars. 



Passing now to the family of flycatchers we find that more 

 than one-fourth of the food of three kingbirds consisted of 

 canker-worms and fully one-half of vine-chafers. The food 

 of three wood-pewees consisted entirely of flying insects. 

 Two specimens of Traill's flycatcher had eaten twenty-five 

 per cent, of canker-worms, and a single yellow-bellied fly- 

 catcher had eaten an equal percentage of vine-chafers but no 

 canker-worms. A single black-billed cuckoo had eaten of 



