Pernice codabianca

Identificazione

The white-tailed ptarmigan is the smallest of the ptarmigans and the smallest bird in the grouse family. 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 11.8 to 12.2 inches (30 to 31 cm) long, with the males being only slightly larger than the females. The average weight is 11.6 to 16.9 ounces (330 to 480 g). During the summer, the white-tailed ptarmigan is a speckled grayish brown with white underparts, tail and wings. In the fall, the plumage has turned a much more reddish-brown color and white feathers begin to grow through. By winter all the summer brown feathers are lost and the bird is completely white. A further molt in the spring precedes the breeding season and the bird returns to its summer plumage. The finely barred greyish coloration on the back makes it easy to distinguish this species from the much browner willow ptarmigan and rock ptarmigan. Both sexes maintain white tail and wing feathers all the year and males can be identified by their reddish eyecombs (fleshy growths above the eye), also present year-long. In general this bird is silent but it sometimes makes quiet, low-pitched hoots and soft clucking noises.

Tassonomia

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.<p>The genus name Lagopus is derived from Ancient Greek lagos (λαγως), meaning "hare", + pous (πους), "foot", in reference to the bird's feathered legs. The species name leucura was for a long time misspelt leucurus, in the erroneous belief that the ending of Lagopus denotes masculine gender. However, as the Ancient Greek term λαγωπους is of feminine gender, and the species name has to agree with that, the feminine leucura is correct. The species name leucura is derived from the Latinized version of the Greek leukos, meaning "white" and oura, meaning "tail", in reference to the bird's permanently white tail.<p>The white-tailed ptarmigan has five recognized subspecies:

Nome scientifico

Lagopus leucura

Autorità

(Richardson, 1831)

Ordine

Galliformi

Famiglia

Phasianidae

Genere

Lagopo

Areale e habitat

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.<p>The white-tailed ptarmigan is the only bird in North America to reside permanently in the alpine zone. Its habitat includes areas of boulders, krummholz, snowfields, rock slides, frost-heaved soil and upland herbage. Even in winter it stays in high valleys and mountain slopes where alder, willow, birch and spruce poke through the snow cover.<p>The white-tailed ptarmigan was introduced into the Sierra Nevada of California 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.<p>The white-tailed ptarmigan was first introduced into Oregon's Wallowa Mountains with 36 birds taken from Colorado and Washington in September 1967. A second set of 54 birds was released in September 1968 that were supplied from Colorado and British Columbia. Although a few of the birds were observed in the spring and summer of 1969 the effort to establish a population in Oregon was ultimately unsuccessful.

Migrazione

Vertical migration

Conservazione

Tendenza della popolazione

declining