178 MIGRATION AND DISTKIBUTION 



your inlorinant mentioned of the hilltop Ptarmigan 

 assuming their winter plumage earlier than the birds 

 lower down shows that the winter there is longer, as of 

 course, might have been predicated, and it is extremely 

 interesting to me to have my observations of the Nor- 

 wegian birds borne out by yours of the Scotch ones. The 

 very fact you mention of the Ptarmigan being scarce 

 on the Sutherland hilltops and plentiful lower down 

 shows that the conditions of their existence on the 

 former are less favourable to them than where less 

 exposed. 



As to Lagopus montanus, as I have said elsewhere, I 

 believe that all the mountain Ptarmigans of Europe 

 (exclusive of Iceland and Spitzbergen) are referable to 

 one and the same species, viz. L. mutus, but I must 

 confess that I have not had all the opportunities I should 

 like of comj^aring Ptarmigans from the Alps and Pyrenees 

 with those of Scotland and Scandinavia. It is true that 

 the Swiss and Pyrenean birds are now completely isolated 

 and cut ol? by a wide interval from their northern 

 brethren, but no one can doubt that there was a time 

 and that (geologically speaking) not so long ago when the 

 range of the species was uninterrupted. Bones of the 

 Willow Grouse and Snowy Owl are found in the French 

 bone-caverns very far south, contemporary with those 

 of the Rein-Deer, and it is pretty plain that as that 

 glacial epoch gradually disappeared bnds of the habits 

 of the Ptarmigan would be driven (by the coming of a 

 warmer climate) to the mountains, while they would 

 cease to exist in the low countries.* 



Although he would never commit himself in his 

 published writings to theories of migration and distribu- 

 tion, he sometimes allowed himself to speculate on such 

 matters in correspondence with his friends : — 



I never made any notes that would be of any use to 

 you on the polar distribution of animals, for I did not 



* LeUer to J. A. Harvie-Bromi. October II, 1869. 



