Bete 
THE MIGRATION OF BIRDS. 343 
however, is an almost insurmountable difficulty to be encountered 
at the very outset. 
Yet some species remain in the same localities throughout the 
year. The gallinaceous birds are true residents of the regions in 
which they raise their young; and many of the Corvide shift 
their quarters very slightly, if at all, in any season. Some of the 
rapacious birds, especially among the owls, are quite stationary ; 
and among the woodpeckers, are species that appear to reside 
constantly in the same localities. Other species, again, seem to be 
indifferently migratory or stationary. Of the vast numbers of 
‘mallards that frequent the ponds and streams of Texas, during 
winter, great numbers are said to remain and breed, while the 
others rove hundreds of miles to the northward. 
In the “ Natural History of the state of New York”* DeKay 
gives the Carolina titmouse as being found in southern New York 
in winter only. If this observation is correct, it affords a unique 
instance of a bird migrating north in winter; but there is good 
reason to doubt the accuracy of the statement. 
The causes of migration are various; but the principal one is 
undoubtedly the want of food. Birds seek a milder climate than 
hat of their native regions, because their means of subsistence 
fail, and they must either obtain it elsewhere, or starve. As soon 
as the chill of autumn destroys the greater number of insects, and 
banishes the remainder to their winter retreats, the insectivorous 
tribes are compelled to migrate to regions where a warmer sun 
sustains a sufficiency of insect life to supply them with food; and 
the granivorous species, finding their usual stores of seeds either 
becoming exhausted or covered with deep snow, follow in their 
track, while rapacious birds are obliged to accompany their prey. 
Only the species whose food-supply is unaffected by the inclem-. 
ency of the season remain. The nuthatch and brown creeper are 
able to find as ample fare in one season, as in another, and a few 
Sparrows find sufficient food in such scattered weed 
s as appea 
above the snow, or amid sheltered nooks and thickets protected 
from the storm. Even in the coldest weather, wherever the cedar 
berries are abundant, we find robins, who refuse to leave as long 
as they can find anything to eat; and bluebirds may be seen amid 
clumps of sumachs, clinging to their northern homes, until com- 
* Possibly, I am mistaken in the reference. = so, the statement is made in Giraud’s 
Birds of Lon g Island.” 
