290 ENTOMOLOGY 



whose exhaustive tables the following- food-percentages are 

 taken : 



Birds Examined. Insects. Canker-worms. 



Robin, 9 93 % 21 % 



Catbird, 14 98 15 



Brown Thrush, 4 94 12 



Bluebird, 5 98 12 



Black-capped Chickadee, 2 100 61 



House Wren, 5 91 46 



Tennessee Warbler, i 100 80 



Summer Yellow Bird, 5 94 67 



Black-throated Green Warbler, I 100 70 



Maryland Yellow-throat, 2 100 37 



Baltimore Oriole, 3 loo 40 



To quote Forbes : " Three facts stand out very clearly as 

 results of these investigations: i. Birds of the most varied 

 character and habits, migrant and resident, of all sizes, from 

 the tiny wren to the blue-jay, birds of the forest, garden and 

 meadow, those of arboreal and those of terrestrial habits, were 

 certainly either attracted or detained here by the bountiful 

 supply of insect food, and were feeding freely upon the species 

 most abundant. That thirty-five per cent, of the food of all 

 the birds congregated in this orchard should have consisted of 

 a single species of insect, is a fact so extraordinary that its 

 meaning can not be mistaken. Whatever power the birds of 

 this vicinity possessed as checks upon destructive irruptions of 

 insect life, was being largely exerted here to restore the broken 

 balance of organic nature. And while looking for their in- 

 fluence over one insect outbreak we stumbled upon at least two 

 others, less marked, perhaps incipient, but evident enough to 

 express themselves clearly in the changed food ratios of the 

 birds. 



" 2. The comparisons made show plainly that the reflex effect 

 of this concentration on two or three unusually numerous in- 

 sects was so widely distributed over the ordinary elements of 

 their food that no especial chance was given for the rise of new 

 fluctuations among the species commonly eaten. That is to 

 say, the abnormal pressure put upon the canker-worm and vine- 



