I40 THE MIGRATION OF BIRDS. 



southern limits of its range it retires to mountains 

 to breed. 



Much shorter yet equally interesting movements 

 in a vertical direction are furnished by a great many 

 endemic mountain species. Wherever the mountains 

 are lofty enough to range from a tropic or sub- 

 tropic zone at their base to a temperate or Arctic 

 climate at their summit, we have numerous instances 

 of vertical migration. In summer these birds ascend 

 into the region that affords them the requisite climate 

 during the season of reproduction, some of course 

 going to much greater elevations than others, to 

 the rhododendron, the pine, or the birch region, as 

 the case may be, and descending with the approach 

 of winter to a more genial climatal zone. Many 

 instances of this kind occur in the Caucasus, the 

 mountains of Turkestan, the Himalayas, the Andes, 

 and elsewhere. In the Alps and the Carpathians, 

 for instance, we find the Alpine Accentor {Accentor 

 alpinus) an endemic species, which visits the highest 

 summits to breed in the Arctic climate above the 

 limit of forest growth, and just below the line of 

 perpetual snow, retiring in winter to the lower 

 valleys. The vertical migrations of some of the 

 Rose Finches [Ccirpodacus) are precisely similar, 

 some of these birds ascending in summer to an 

 elevation of 10,000 feet, and wintering in the lower 

 valleys. 



From all these facts it will be seen that vertical 

 migration is very similar to latitudinal migration, 

 and that it is undertaken for purposes precisely the 



