Coloration evidence for natural selection J. Bowler wrote that Darwin's theory In his 1889 book "Darwinism", the naturalist Alfred Russel Wallace considered the white coloration of Arctic animals. He recorded that the Arctic fox, Arctic hare, ermine and ptarmigan change their colour seasonally, and gave "the obvious explanation", that it was for concealment. The modern ornithologist W. L. N. Tickell, reviewing proposed explanations of white plumage in birds, writes that in the ptarmigan "it is difficult to escape the conclusion that cryptic brown summer plumage becomes a liability in snow, and white plumage is therefore another cryptic adaptation." All the same, he notes, "in spite
Rock ptarmigan the Russian High Arctic overwinters during the polar night and survives by feeding on rich vegetation on and underneath high cliffs where seabird colonies are located in summer.<ref name="FJL/">Dinets, V. (2001) Winter ecology of Willow Ptarmigan "Lagopus lagopus" and Rock Ptarmigan "L. mutus" at the northern limit of their range. "Ornitologia" 29: 326-327 (in Russian with English summary).</ref> During the last ice age, the species was far more widespread in continental Europe. The rock ptarmigan feeds primarily on birch and willow buds and catkins when available. It also eats various seeds, leaves, flowers, and berries of other plant species. Insects