122 



USEFUL BIRDS. 



tain plant lice ; and two years previously I had published a 

 list of thirty-four species which feed upon plant lice. It is 

 a widely known fact in Massachusetts that practically all of 

 the resident and migrant Warblers eat the birch plant louse. 

 It is only necessary for one to find a locality where these 

 insects are numerous if he wishes to make sure of finding in 

 their seasons about all the Warblers that breed in that region 

 or migrate through it, and also many other birds not ordi- 

 narily found among the birches. Trees are seldom killed 

 by plant lice ; but they are often seriously weakened, their 

 fruitage lessened, and their growth greatly retarded by the 

 attacks of these prolific creatures. Undoubtedly the plant 

 lice of the birch would greatly reduce the annual crop of 

 birch wood and lumber were it not for the manner in which 

 their increase is checked by birds. A list of thirty-eight 

 species of birds that have been found, either by myself or 

 my assistants, feeding on birch plant lice, is appended : 



Downy Woodpecker. 



Northern Flicker. 



Chimney Swift. 



Ruby-throated Hummingbird. 



Wood Pewee. 



Least Flycatcher. 



Purple Finch. 



Rusty Blackbird. 



Red-winged Blackbird. 



Baltimore Oriole. 



American Goldfinch. 



Slate-colored Junco. 



Chipping Sparrow. 



White-throated Sparrow. 



Field Sparrow. 



Bobolink. 



Towhee. 



Rose-breasted Grosbeak. 



Indigo Bunting. 



Chickadee. 



Scarlet Tanager. 



Red-eyed Yireo. 



Yellow-throated Vireo. 



Black and White Warbler. 



Myrtle Warbler. 



Parula Warbler. 



Yellow Warbler. 



Blaek-throated Blue Warbler. 



Magnolia Warbler. 



Chestnut-sided Warbler. 



Northern Yellow-throat. 



Black-throated Green Warbler. 



Black-poll Warbler. 



Oven-bird. 



American Redstart. 



Catbird. 



White-breasted Nuthatch. 



American Robin. 



Some of the evidence from w r hich my conclusions were 

 drawn regarding the economic relations existing between 

 birds on the one hand and plant lice and hairy caterpillars 

 on the other, is here presented, that the reader may have an 



