BIRDS AS REGULATORS OF OUTBREAKS. 



69 



Nine robins had eaten only animal food, of which canker- 

 worms formed twenty, cutworms twenty-eight, and vine- 

 chafers fourteen per cent., making a total of sixty-two per 



APPLE-LEAVES ATTACKED BY CANKER-WORMS. 



cent, for these three groups of insects. Eleven per cent, of 

 the remainder consisted of- click-beetles (Elateridce). Fourteen 

 cat-birds were examined : they had eaten fifteen per cent, of 

 canker-worms, ten per cent, of cutworms and other cater- 

 pillars, fourteen per cent, of ants, and thirty-three per cent, 

 of vine-chafers. Four brown thrushes had eaten canker- 

 worms, vine-chafers, June-beetles, click-beetles, ground-beetles, 

 and other insects. Combining these food elements of twenty- 

 seven members of the thrush family, Professor Forbes found 

 that " none of them had eaten any vegetation whatever ; 

 that ninety-six per cent, of their food consisted of insects 

 (myriapods and earthworms making up the remaining four 

 per cent.) ; that sixteen per cent, was canker-worms, and 

 only four per cent, predaceous beetles." The vine-chafer 

 made just twenty-five per cent, of the entire food. 



The most important element in the food of five bluebirds 

 was the vine-chafer (thirty-six per cent.), while canker-worms 

 formed twelve per cent. Two black-capped chickadees had 



