CHAPTER Iir 



THE CHANGES OF PLUMAGE IN THE RED GROUSE IN HEALTH AND IN DISEASE 



By Edtvard A. Wilson 

 Part I. — Plumage Changes of the Cock Grouse 



When a large number of skins of the cock Grouse are arranged together, side 

 by side, according to the month in which the birds were killed, it will be found 

 that, even taking into account the diflerences of well-marked local variations in 

 plumage, the series can readily be divided into two very distinct sets. 



There is first a very marked uniformity in the plumage of the cock 

 birds killed from the middle of November to the end of June ; and 

 likewise amongst those killed from the end of June to the middle changes of 

 of November. 



These two periods, November to June and June to November, mark the two 

 seasonal changes of plumage in the cock Grouse. 



The first is a plumage ^vorn throughout the ivinter, as well as during the 

 courting and breeding season of the sjmng. 



The second is a plumage ivorn throughout the late summer and early autumn. 



It is necessary to lay stress upon this general broad division of the cock 

 Grouse's plumage, and if a large number of skins can be arranged as suggested 

 the time at which the Grouse has definitely changed from the one plumage 

 to the other cannot possibly be overlooked. The birds obtained at the end of 

 May are definitely in the darker and redder winter plumage, and those procured 

 at the end of June are definitely in the paler and more bufi'-coloured summer 

 plumage ; those killed at the beginning of October are still partly in the 

 paler summer plumage, and by the end of November all are in the darker 

 winter plumage. 



^ Reprinted from tlie Proceedings of the Zoological Society of London, 1910, 



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