Natural History 469 



in winter, all but the black tips of its ears; in Ireland there is not 

 usually any seasonal change of colour. 



The Story of the Snow-Mouse 



One of the most definitely mountain-haunting mammals is 

 the Snow-Mouse, or, accurately, Snow-Vole (Microtus nivalis) 

 of the High Alps. It is a little creature about five inches long in 

 body and two more in tail, usually rusty-grey or whitish-grey in 

 colour. Perhaps it has the honour of living a harder life than 

 any other mammal, for it is rare below 4,000 feet, and it ascends 

 from the snow-line to the tops of the mountains. It does not 

 migrate in winter; it does not hibernate; and it does not turn 

 white. In fact, its only adaptation to its snowy retreats is that 

 in the summer it gathers to its nest among the loose rocks a store 

 of chopped grass and gentian roots. In winter it makes tortuous 

 burrows beneath the snow, mining its way from one Alpine plant 

 to another. It has the reward of freedom from enemies, for even 

 birds of prey are scarce at these heights. The explanation of the 

 habitat is interesting. The snow-mouse used to be one of the 

 "tundra" animals, like the Reindeer and Arctic Fox, that fre- 

 quented the low grounds of Central Europe when the uplands 

 were covered by a great ice-sheet. As the climate became milder 

 and the ice-sheet melted, some of the "tundra" animals, like the 

 Reindeer and Arctic Fox, retreated northwards, but the Snow- 

 Mouse went up the mountains, higher and higher. Thus we also 

 understand why they have to-day a scattered distribution, 

 separated by extensive mountainous tracts where none occur. 

 This corresponds to some extent to separate migrations from the 

 low grounds ; it also has to do with the available vegetation, for 

 the hardy Snow-Mouse must eat something. 



9 



Mammals show a thousand and one adaptations connected 

 with procuring and utilising their food, and we cannot give more 

 than a few illustrative examples. 



