334 HISTORY OF THE EUROPEAN FAUNA. 



cannot altogether be explained by the supposition of 

 an interchange in the faunas of the two regions. That 

 this has taken place to some extent is probable, but 

 the resemblance appears more especially due to the 

 fact that the Alps and Scandinavia have been peopled 

 from the same centres of distribution. 



In order to make this matter quite clear, I will give 

 a familiar example as an instance of the manner in 

 which the present distribution can be explained with- 

 out taking recourse to direct migration from the Alps 

 to Scandinavia or vice versa. The example I will 

 take is that of a family of birds, not only of extreme 

 interest from the fact of its northern range, but also 

 from the pleasure it gives to those addicted to sport. 

 This is the grouse family, the Tetraonida. 



Let us commence with our British Grouse (Lagopus 

 scoticus\ which is peculiar to the British Islands. 

 In Norway we find a Grouse (L. albus) which differs 

 in habit, and in the fact of its turning white in 

 winter ; otherwise it is so closely allied to our 

 Grouse that many ornithologists do not separate 

 them specifically. No doubt the British Grouse is a 

 descendant of this Scandinavian Willow-grouse. The 

 latter is known also to inhabit Greenland and Arctic 

 North America, and it is even found beyond Behring 

 Straits in Northern Siberia. En route between 

 Scandinavia and Asia, travelling in a westward 

 direction, we meet with two other very local species 

 of Grouse, which may be looked upon as offshoots 

 of L. rnpestris viz., L. hyperboreus of Spitsbergen, 



