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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