132 OBSERVATIONS ON CANADIAN BIRDS, 
al 
largely to the support of the birds of prey, and in the southern part 
of the continent, are, during the winter, taken in numbers with the 
net, and sold for the table. None of these causes, however, in 
any way affect the class which embraces the Fly-catchers and 
Warblers, as from their small size and the nature of their food, 
they are not sought after for these purposes. The check which applies 
to this class must therefore be of a different description from those 
referred to, and finding no way in which their numbers are reduced to 
any extent, except by the sacrifice made of their own young while 
rearing that of the Cowbird, leads me to conclude, that the habit 
has been given for the special purpose of keeping within proper 
bounds, a class of birds which might otherwise have exceeded 
their due proportion in the economy of nature. If we suppose the 
habit to be the result of any physical defect in the Cowbird, we might 
naturally expect, that it would confide the care of its young to a bird 
nearly allied to its own species, but in nine cases out of ten, the foster 
parents belong to a group which are different both in size, habit, and 
the nature of their food ; it is evident therefore that the result of the 
peculiarity is intended by nature to bear specially on the class to 
which the foster parents belong, and any one who has noticed the 
flocks of cowbirds which pass along on their migratory course in 
spring and fall, and estimated that for each bird in these flocks, 
from three to five of a different class have been prevented from 
coming to maturity, must admit that it is no small influence which 
the Cowbird exercises, in maintaining the balance of power which 
so admirably prevails among the feathered tribes. 
If we could imagine such a thing in nature, whose movements are 
all so well ordered as that the. Cow Buntings should at any time get in 
excess of the other class referred to, it would be curious to estimate 
the results ; the Flycatchers would then be fully occupied in rearing 
foster children, and not being permitted to perpetuate their own 
species, must soon die out, when the Cowbirds, finding themselves 
without a substitute in the rearing of their young, would either be 
driven by necessity to make the attempt themselves, or they too 
would soon be added to the list of extinct species. 
Passing the Jays and the Crows, (both of which are well deserving 
of notice did our limits permit,) we come to a speeies, which, in our 
vicinity, is the sole representative of his family.* This is the American 
* Since writing the above, I have found a second species near the city, which appears to 
be the Lanius Excubitorotdes of Baird. 
