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 vegetation in the spring, and flower and set seed much sooner than plants that grow in warmer conditions. Their peak metabolic rate also occurs at a much lower temperature than plants from farther south. Compact cushions of vegetation keep the plants close to the warm soil and shield the tender central growing shoot. The height of Arctic plants is also governed by snow depth. Plants that protrude above the snow are subject to strong winds, blowing snow, and being eaten by caribou, muskox, or ptarmigan. Mosses and lichens are common in the Arctic. These plants have the ability to stop growth