Introduction

This ptarmigan, the smallest grouse in North America, inhabits alpine areas at or above timberline in the mountain cordilleras of the west. Physiological, behavioral, and life history adaptations that conserve energy and enhance its ability to hide have allowed this ground nesting herbivore, which subsists on buds and leaves, to thrive in such cold, open, arid, and low-oxygen environments. In winter, for example, flocks are known to roost within snowbanks and individuals develop feathered tarsi that function as snowshoes. In addition, these birds tolerate a wide range of temperatures without expending excess energy. They generally walk rather than fly and in bad weather select microhabitats several degrees warmer than ambient temperature. Different calls identify a predator as avian or mammalian. Individuals respond to avian predators by crouching near or under rocks.

Like its arctic congeners, the Willow Ptarmigan (L. lagopus) and Rock Ptarmigan (L. mutus), the White-tailed Ptarmigan is noted for plumage that changes from white in winter to brown in summer. This is the southernmost species of ptarmigan, with populations extending from south-central Alaska to northern New Mexico. Because alpine areas have remained relatively undisturbed, this species still occupies most of its historic range.

Its cryptic plumage and behavior, and the inaccessibility of its alpine habitat, has hindered detailed examination of its life history. Most knowledge of the ecology of White-tailed Ptarmigan comes from studies of L. l. altipetens in Colorado. The unpublished data in this review were collected by CEB during 1966–1992 at Mt. Evans and Rocky Mountain National Park, Colorado, and by KM during 1987 and 1989–1992 at Mt. Evans, Guanella Pass, and Loveland Pass, Colorado.