The Birds’ Calendar 
and larvee of insects abundant in the bark of so 
many trees, and also in the meagre supply of 
berries and seeds still clinging to the branches 
and to the dead stalks of last year’s growth. 
And, by the way, we are greatly indebted to 
these graceful and unobtrusive little scavengers 
for their constant service in ridding the trees of 
that which, if allowed to live and develop, would 
prove so injurious, if not fatal, to our forests. 
Thus, from one and the same cause, as cold 
weather approaches, the more northern species 
come to us, and our own summer birds go 
south, while in spring the migration is reversed. 
This accounts for the semi-annual appearance 
and disappearance of the two groups known as 
summer residents and winter residents, which 
being with us for the longest periods comprise 
all the best-known species. It should be re- 
marked in this connection that the permanence 
of some species remaining in one locality the 
year round is doubtless often secured by replace- 
ment of some individuals going south by har- 
dier ones from the north, and wzce versa. 
In anatomy and habits the several species of 
each of these two groups are widely different 
from each other. Size is no criterion of hardi- 
ness, as some of the smallest birds are the most 
52 
