SONG BIRDS OF ORCHARD AND WOODLAND. 185 



WARBLERS. 



Of the twenty-five species and two sub-species of AVar- 

 blers that may be confidently looked for each spring in 

 Massachusetts, either as migrants or residents, only eight 

 are generally distributed throughout the State in the breed- 

 ing season, and two of these are rather local. Several other 

 species breed here, but only locally or rarely. Only the 

 more common familiar summer resident species, which are 

 of great economic importance, will be mentioned here. The 

 migrants are of great though lesser importance. Their 

 abundance in migration is probably governed largely by 

 the number of insects to be found upon the trees. When- 

 ever large numbers of Warblers are seen here in migration, 

 their presence may be taken as an indication of a plenti- 

 ful supply of the arboreal insects on which chiefly they 

 feed. The fact that Warblers live mostly on small insects 

 does not lessen their usefulness, it may even make them 

 more valuable. Warblers are undoubtedly responsible for 

 the destruction of many of the young caterpillars of the 

 great cecropia, promethea, and luna moths, which, while 

 still too small to do any harm, are killed off by birds. It 

 should be noted also that many of the greatest pests are very 

 small even at maturity. The onion fly, the Hessian fly, the 

 wheat midge, and many injurious Lepidoptera and Cole- 

 optera are among the tiny insects that are eaten by small 

 birds. Only the smaller birds can follow insects to the tips 

 of the slenderest twigs ; therefore, the smaller the bird the 

 greater its special usefulness. 



We have already seen that Warblers have a great capacity 

 for destroying small insects. In migration they seem to 

 possess most remarkable appetites. Rev. Leander S. Keyser 

 watched a Hooded Warbler, and found that it caught on the 

 average two insects a minute, or one hundred and twenty an 

 hour. He estimates that at this rate the bird would kill at 

 least nine hundred and sixty insects a day, assuming that it 

 sought them but eight hours. 1 



1 Papers presented at the World's Congress on Ornithology, 1896, pp. 41, 42. 



