The Birds’ Calendar 
one of the very latest warblers is the ‘‘ black- 
poll,’’ which was still here June 4th. But the 
main host makes its passage between the mid- 
dle of April and the middle of May. 
The area occupied summer or winter by any 
species can never be stated with precision, as it 
will vary somewhat even from year to year. 
According to temperature and other conditions, 
the ‘‘ wave’’ may sweep a little farther north or 
south. A winter species may not appear for 
several years, and then be reported in great 
numbers. I think this is the case this winter 
in New England with the pine grosbeak, which 
has been rare for many seasons, and now seems 
to be quite plentiful, one correspondent inform- 
ing me he has seen hundreds of them. The 
severity of climate and perhaps scarcity of food 
have evidently driven them in great numbers 
from the north. 
As we approach the boundaries of its range, 
the individuals of a species are likely to become 
more and more infrequent, which makes the 
range more difficult to determine. But the 
increasing rarity of a species toward its boun- 
daries, and the uncertainty involved in their 
fluctuating movements, give additional zest in 
the search for specimens. 
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