Plump chickenlike bird found in rocky tundra and alpine summits. Plumage changes strikingly throughout the year. In winter, both sexes are pure white with black outer tail feathers. As summer progresses, male develops cold grayish-brown feathers on head, neck, and back; generally quite splotchy looking. Summer female is paler golden-brown with intricate black and white markings. Female nearly identical to Willow Ptarmigan; look for slightly smaller bill. Summer male Willow and Rock Ptarmigans can be separated by the colder grayish plumage on Rock Ptarmigan and in winter by the distinctive black eyeline on Rock Ptarmigan. Also note habitat differences. Best distinguished from White-tailed Ptarmigan by black outer tail feathers. Vocalizations include guttural groaning and clucking notes.