白尾雷鸟种

其羽毛颜色随着季节的不同会发生变化，在夏天通常有灰色、褐色或白色斑点，冬季则完全变成白色。全年翅膀、腹部和尾巴都是白色的。白尾雷鸟以植物的花叶种子为食。其巢穴就筑在地上，一次最多产8枚卵。其数量稳定。

The white-tailed ptarmigan (Lagopus leucura), also known as the snow quail, is the smallest bird in the grouse tribe. It is a permanent resident of high altitudes on or above the tree line and is native to Alaska and the mountainous parts of Canada and the western United States. Its plumage is cryptic and varies at different times of the year. In the summer it is speckled in gray, brown and white whereas in winter it is wholly white. At all times of year the wings, belly and tail are white. The white-tailed ptarmigan has a diet of buds, leaves, flowers and seeds. The nest is a simple depression in the ground in which up to eight eggs are laid. After hatching, the chicks soon leave the nest. At first they eat insects but later move on to an adult diet, their mother using vocalisations to help them find suitable plant food. The population seems to be stable and the IUCN lists this species as being of Least Concern.

Taxonomy and etymology

The white-tailed ptarmigan was given the scientific name Tetrao (Lagopus) leucurus by the Arctic explorer John Richardson in 1831. It was later determined that Lagopus had sufficient distinguishing features to be regarded as a separate genus and the bird became Lagopus leucurus. Molecular studies have shown that Lagopus is monophyletic, with the rock ptarmigan (Lagopus muta) and White-tailed ptarmigan being sister species. The position of the willow ptarmigan (Lagopus lagopus) is less clear cut, it showing some genetic divergence over its wide range.

Description

The white-tailed ptarmigan is the smallest of the ptarmigans and the smallest bird in the grouse tribe. It is a stocky bird with rounded wings, square-ended tail, small black beak and short legs with feathering extending to the toes. Adults are 31 to 34 centimetres (12 to 13 in) long, with the males being only slightly larger than the females. The average weight is 325 grams (11.5 oz). During the summer, the white-tailed ptarmigan is a speckled grayish brown with white underparts, tail and wings.

Distribution

The white-tailed ptarmigan is an alpine species, a permanent resident of the high mountains above or near the timber line. It occupies open country and flies a great deal more than forest grouse, but still prefers running to flying. It ranges from Alaska and western Canada south to northern New Mexico. Males return from their wintering areas to establish territories on spruce-willow timber line breeding grounds in April. Females arrive in early May and pairs are formed.

The white-tailed ptarmigan is the only bird in North America to reside permanently in the alpine zone.

Diet

This herbivorous bird's diet varies seasonally. Nitrogen-rich snow buttercup leaves are favored in the spring season, while willow catkins, mountain avens flowers, and chickweed blooms, other flowers and leaves, lichens and berries form the majority of the ptarmigan's diet in the summer. Once fall and winter arrive in the region, the ptarmigan feeds on pine needles, seeds, willow and alder buds and twigs. Winter food sources have a much higher cellulose content than does summer forage, so the ptarmigan relies on bacteria-aided digestion in the cecum to extract essential nutrients.

Breeding

White-tailed ptarmigan males are usually monogamous and remain with the same mate for one breeding season. To attract females, a male will strut and display his tail feathers. The female builds a simple scrape nest on the ground, while the male acts as a sentry to guard the area. The nest is a shallow depression in a snow-free area, generally protected from the wind and is softened with grasses and a few feathers. One side of the nest generally provides a quick escape route.

Adaptations and status

The white-tailed ptarmigan is well-camouflaged when on the ground. In his pioneering 1909 book on the subject, Concealing-Coloration in the Animal Kingdom, the American artist Abbott Thayer wrote:

There is perhaps no other bird which moults as gradually as the Ptarmigan, and this fact goes very far to strengthen the supposition that it has developed a peculiarly fluid and perfect system of protective coloration. Figs. 8, 9, 10 and 39 show White-tailed Ptarmigans, of the Rocky Mountains, in winter and transitional plumages...