SONG BIRDS OF ORCHARD AND WOODLAND. 185 
WARBLERS. 
Of the twenty-five species and two sub-species of War- 
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. 
