THE WHITE WINTER COAT 



\ FAMILIAR human reaction to the conditions of life in 

 Ji\. winter is a change of dress. We clothe ourselves in 

 the skins of other mammals, putting on layer after layer of 

 wool, and, it may be, a fur coat on the top. Similarly it is 

 known of many mammals that they grow a thicker and longer 

 coat of hair as the days become colder. But what concerns 

 us now is the change of colour to white, as we see it, for 

 instance, in the mountain hare, among mammals, and in 

 the ptarmigan, among birds. How does this change come 

 about, and what is its significance ? 



In the first place, as to the occurrence of this peculiarity of 

 changing to white in winter, it is exhibited by distinctively 

 Northern creatures the Arctic fox (Canis lagopus), the 

 Hudson's Bay lemming (Cuniculus torquatus), the ermine 

 (Mustela erminea), the mountain hare (Lepus variabilis), the 

 American hare (Lepus americanus), and the ptarmigan 

 (Lagopus albus). This is interesting, since permanent white- 

 ness is characteristic of many Northern animals, such 

 as Polar bear and American Polar hare, Greenland falcon, 

 and snowy owl. It is probable, therefore, that changing 

 to white is advantageous for the same reasons as permanent 

 whiteness. 



It is also instructive to notice that some of the mammals 

 that usually turn white do not always change, and that this 

 is connected with the habitat. Thus the Arctic fox (Canis 

 lagopus) does not usually turn white in Iceland ; the 

 mountain hare rarely changes in Ireland ; and white stoats 



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