122 



USEFUL BIRDH. 



tain })lant lice ; and two years previously I had published a 

 list of thirty-four species which feed upon plant Uce. 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 necessarj' for one to find a locality where these 

 insects are numerous if he wishes to make sure of findina; 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. Undoubtedl}^ 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 1)y l)irds. A list of thirty-eight 

 species of ])irds that have been found, either by myself or 

 my assistants, feeding on 1)ircli plant lice, is appended : — 



Downy Woodpecker. 



Nortliern Flieker. 



Chimney Swift. 



Ruby-throated I Iiniimingljird. 



Wood Pewee. 



Least Flycatcher. 



Purple Finch. 



Rusty BlaeklMrd. 



Red-win<i;ed l>laekl)ird. 



Baltimore Oriole. 



American Goldfinch. 



Slate-colored Junco. 



Chijjping Sparrow. 



White-throated Sparrow. 



Field Sparrow. 



Bobolink. 



Towhee. 



Rose-breasted Clrosl>eak. 



Indiifo Buntino-. 



Chickadee. 



Scarlet Tanager. 



Red-eyed Vireo. 



Yellow-throated A'ireo. 



Black and 'White ^A'arbler. 



Myrtle Warbler. 



Parula Warbler. 



Yellow AVarbler. 



Black-throated Blue A\'ar])ler. 



Magnolia Warbler. 



Chestnut-sided Warbler. 



Northern Yellow-throat. 



Black-throated (ireen "\\'arbler. 



Black-poll AVarbler. 



Oven-l:)ird. 



American Redstart. 



Catbird. 



White-1 )reasted Nuthatch. 



American Robin. 



Some of the evidence from which my conclusions were 

 drawn regarding the economic relations existing between 

 birds on the one hand and jjlatit lice and hairy caterpillars 

 on the other, is here jH-esented, that the reader may have an 



