1000 DU. E. A. WILSON OS THE [June 14, 



5. The Changes of Plinnago in the Kcd Grouse {Latjopxis 

 scodciis Lath.) in Health and in Disease. By Edward 

 A. Wilson, M.B., F.Z.S., FieUl-Observer to the Grouse 

 Disease Inquiry.* 



[KeceivcJ .luiif 11, 1910.] 



(Plates LXXVIII.-CI.t & Text-figure 150.) 



Part I. 

 Plumage Changes in the Cock Grouse. 



When a large number of skins of the cock Grouse are 

 arriingeil together, side by side, according to the month of the 

 3'eai' in which the birds were killed, it will be found that, even 

 takinfif into account the differences of well-mai-ked local vari- 

 ations in i)luinage, 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 tlie middle of November to the end of 

 June ; and likewise amongst those killed from the end of June 

 to the middle of November. 



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

 mark the two seasonal changes of plumage in the cock Grouse. 



The jirst is a phmiage worn throughout the winter, as well as 

 during the courting- and breeding-season of the spring. 



The second is a ])lumage worn throughoiot the summer and 

 autumn. 



It is necessary to lay stress u])on this general broad division 

 of the cock Grouse's plumage, and if a large number of skins 

 can be arranged as suggested, the exact time at which the 

 Grouse has definitely changed from the one plumage to the 

 other cannot possil)ly be overlooked. The bii-ds obtained at 

 the end of IMay are definitely in the dai-ker and redder winter- 

 plumage, and those procured at the end of June are definitely 

 in the paler and more buft-coloured summei'-plumage ; those 

 killed at the beginning of October are still j)aitly in the paler 

 sunniier-plumage, and by the end of Novendjer all are in the 

 dai-ker winter-plumage. 



It must, however, he added, that there is hardly a month in 

 the whole year, or a Grou.se-skin in a collection of many hundreds 

 covering every month of the year, in which one plumage only can 

 be found innnixed witii the other. This fact accoinits largely for 

 the misunderstanding which at one time existed, but which lias 

 now, we ho[)e, been sjitisfactorily settled, in res^jcct of the whole 



* Owing to Dr. Wilson Laving U'ft London on the Antarctic Exiu'dition before 

 fbis Mi'Uioir was sot up in fy|)f, lie was unable to n-vise the i)roofs, but lett full 

 jiower to the Editor ami Mr. W . K. Ogilvie-Gnint, who have nnide certain modi- 

 fications in the text. 



t For explanation of the I'lates sec p. 1032. 



