The Rock Ptarmigan is Nunavut's official bird. It is truly a bird of the Arctic because, unlike most other Arctic birds, it remains there year-round.

The Rock Ptarmigan is about 27 to 40 cm (11 to 16 in.) long. The end of its tail is square, and it has a small black bill. Unusually, this species has three seasonal plumages—most birds have only two: the Rock Ptarmigan's feathers moult and change colour for summer, autumn and winter. The colours help the birds blend into their surroundings, thereby helping them keep safe from predators.

During the breeding season in spring, females change to the summer plumage that has a barred pattern of brown, black and gold. Males stay white longer, but by late summer they look similar to the females.

As autumn approaches, males and females turn greyer. They barely complete this moult before they begin to change for winter.

In winter, both the males and the females are white, except for black feathers in the tail that are visible when the tail feathers are spread. Males, and some females, also have a black stripe that extends from behind each eye to the bill. The stripe apparently reduces glare in the eyes.

Both males and females have a red comb above their eyes, but it is barely visible in females. The comb is always quite visible in males, and it becomes especially evident when they are courting or defending their territory because it engorges with blood, and so grows (temporarily) larger and more prominent.

Rock Ptarmigans have feathers covering their legs and feet that help them survive the Arctic climate. Not only do these feathers help keep them warm in winter, but they help the birds walk on top of the snow because the feather-widened feet act like snowshoes, distributing the bird's weight over a larger area.

Rock Ptarmigans can be found in all the countries that circle the North Pole, including northern North America, Asia, Europe, Iceland and Greenland, and also in mountainous parts of southern Europe.