ISLAND AVIFAUNAS 193 



Europe, and the evidence strongly suggests that the 

 range of this Grouse reached far to the south-east, from 

 Scandinavia and North Russia as far as the Caucasus 

 (where it is probable this Grouse will yet be discovered 

 as an indigenous species ; at least one example has been 

 obtained there), Asia Minor, and Turkestan. Owing to 

 its arboreal habits, it soon became exterminated in the 

 north, its disappearance followmg that of the willows 

 and birches. The birds inhabiting what was then the 

 British portion of continental Europe were likewise 

 exterminated in the north by the glacial climate, say to 

 limits that reached from 53° north latitude, down to the 

 Pyrenees. In the course of time the great glaciers and 

 snow-fields of Central Europe completely isolated the 

 two colonies of Grouse. Those in the south-west were 

 probably never exposed to such a severe climate as the 

 individuals dwelling in the south-east. Be that as it 

 may, there can be no doubt that the Willow Grouse that 

 occupied that portion of the Pre-Glacial range of the 

 species composing Refuge Area I. during the Ice Age 

 were the ancestors of the Red Grouse, and must have been 

 differentiated to a certain extent by their isolation at 

 that period. During their long sojourn in this area, in 

 their probably severe struggle to maintain themselves, 

 they became heath or tundra birds, compelled to give 

 up their arboreal habits ; and as the climate ameliorated 

 and their descendants gradually spread north again, 

 they would naturally keep to those districts that pre- 

 sented the least changed conditions — the mountainous 

 areas, the watersheds and moors — as they still continue 

 to do, not emigrating across the low fertile plains of the 



North Sea Area, and perhaps finding no country suited 



O 



