White-tailed ptarmigan cover. The white-tailed ptarmigan was introduced into the Sierra Nevada of California, Wallowa Mountains in Oregon, and Uinta Mountains of Utah in the 1970s. It may have been native here during the early Pleistocene but became locally extinct due to climate changes with greater snow-cover in spring impacting on its breeding season. Alternatively, it may have been unable to colonize the Sierra Nevada because of the barriers provided by the Columbia River and the Great Basin, and the low altitudes of the intervening South Cascades. This herbivorous bird's diet varies seasonally. Nitrogen-rich snow buttercup leaves are favored in the spring
Arctic fox pads are covered in fur. There are two genetically distinct coat color morphs: white and blue. In the winter the white morph is white in color and turns brown along the back with light grey around the abdomen in summer. The blue morph is often a dark blue, brown, or grey color year-round. Although the blue allele is dominant over the white allele, 99% of the Arctic fox population is the white morph. The fur of the Arctic fox provides the best insulation of any mammal. The fox has a low surface area to volume ratio, as evidenced by its