Snow camouflage as Hugh B. Cott have echoed his observations, adding that other animals of the Arctic such as musk ox, moose, reindeer, wolverine and raven never become white "even in the coldest parts of their range". Cott noted that both animals that hunt, like polar bear and stoat, and prey animals like ptarmigan and mountain hare, require camouflage to hide from prey or from predators respectively. There is little experimental evidence for the adaptiveness of white as camouflage, though the ornithologist W. L. N. Tickell, reviewing proposed explanations of white plumage in birds, writes that in the ptarmigan "it is difficult
White-tailed ptarmigan is wholly white. At all times of year the wings, belly and tail are white. The white-tailed ptarmigan has a diet of buds, leaves, flowers and seeds. The nest is a simple depression in the ground in which up to eight eggs are laid. After hatching, the chicks soon leave the nest. At first they eat insects but later move on to an adult diet, their mother using vocalisations to help them find suitable plant food. The population seems to be stable and the IUCN lists this species as being of "Least Concern". The white-tailed ptarmigan was given the scientific