THE ST. KILDA WEEN 



(Troglodytes liirtensis) 



It is a singular fact in the ornithology of the British Islands 

 that so few of the birds found resident in them are peculiar 

 to the country, and one that seems conclusively to prove that 

 the separation of these islands from the continent of Europe 

 has, geologically speaking, been comparatively recent. When 

 the ornithologist begins to study his favourite science more 

 deeply, and especially in relation to its bearing on the origin 

 of species, he will find much to interest him. He will be able 

 satisfactorily to determine the history of many species, and 

 clearly to trace the descent of many local forms and isolated 

 races from the parent stock. In this country his examples of 

 the evolution of species by the agency of isolation are ex- 

 tremely few, but quite sufficient to illustrate very forcibly 

 this law of the origin of species. One of the most interesting 

 examples is to be found in the Eed Grouse, a bird which is 

 only found in the British Islands. This bird is very closely 

 related to the Willow Grouse, a species that lives as close to 

 this country as Scandinavia, and which, like the Ptarmigan, 

 assumes a snow-white winter plumage.. Indeed, the Eed 

 Grouse is nothing^ more than an island form of the Willow 

 Grouse, its chief point of distinction being its constant brown 

 dress. In accounting for the presence of the Eed Grouse 

 in this country, we can either presume that the range of the 

 Willow Grouse became discontinuous when our islands were 



