114 USEFUL BIRDS. 
tions may be questioned by those who rely solely upon the 
examination of stomach contents to determine the food of 
birds ; but for the purpose for which these investigations are 
made they are, if skilfully conducted, quite as serviceable 
as stomach examinations. In fact, one must supplement the 
other. Were one to follow the birds about through the. 
fields and woods, no doubt some interesting facts might be 
learned in regard to their food; but it is not in this way 
that a series of accurate observations can be made. For 
our purpose, the method pursued was to find an outbreak 
of hairy caterpillars situated in a locality where many spe- 
cies of birds would be likely to find it. The watcher first 
made sure as to the kind of insects to be found upon the 
trees or plants to be watched; he then concealed himself 
near the insects whose destruction he wished to observe, and 
watched the birds which came there to feed. When this 
method is followed methodically by trustworthy, painstaking 
naturalists, and when results obtained by different observers, 
working independently, agree in the main, there can be no 
reasonable doubt as to the value of such observations. When 
the caterpillars are small, certain marked branches are selected 
to be watched, or certain nests, webs, or tents are studied at 
close range. By this method, as well as by stomach exam- 
inations, fifty-one species or subspecies of birds were found 
to be feeding to a greater or less extent upon hairy cater- 
pillars. A list of these is given below. It will be seen 
that it comprises most of the common summer birds found 
in Massachusetts woodlands, and some not commonly found 
there. 
Birds observed feeding on Hairy Caterpillars. 
Yellow-billed Cuckoo. 
Black-billed Cuckoo. 
Hairy Woodpecker. 
Downy Woodpecker. 
Yellow-bellied Sapsucker. 
Northern Flicker. 
Kingbird. 
Crested Flycatcher. 
Pheehe. 
Wood Pewee. 
Least Flycatcher. 
Blue Jay. 
Crow. 
Red-winged Blackbird. 
Baltimore Oriole. 
Purple Grackle or Crow Blackbird. 
Bronzed Grackle. 
White-throated Sparrow. 
Chipping Sparrow. 
Field Sparrow. 
Song Sparrow. 
Towhee. 
