The Birds' Calendar 



and larvx 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 vice 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 



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