Pernice bianca

Identificazione

The rock ptarmigan is 34–36 cm (13–14 in) long with an 8 cm (3.1 in) tail and with a wingspan of 54–60 cm (21–24 in) and a weight of .mw-parser-output .frac{white-space:nowrap}.mw-parser-output .frac .num,.mw-parser-output .frac .den{font-size:80%;line-height:0;vertical-align:super}.mw-parser-output .frac .den{vertical-align:sub}.mw-parser-output .sr-only{border:0;clip:rect(0,0,0,0);clip-path:polygon(0px 0px,0px 0px,0px 0px);height:1px;margin:-1px;overflow:hidden;padding:0;position:absolute;width:1px}440–640 g (15+1⁄2–22+1⁄2 oz). It is smaller than the willow ptarmigan by about ten percent.<p>The rock ptarmigan is seasonally camouflaged; its feathers moult from white in winter to brown in spring or summer. The breeding male has greyish upper parts with white wings and under parts. In winter, its plumage becomes completely white except for the black outer tail feathers and eye line. It can be distinguished from the winter willow ptarmigan by habitat and markings—the rock ptarmigan prefers higher elevations and more barren habitat. It also has a slender bill and a black eye stripe, which is absent in the willow ptarmigan.

Tassonomia

The rock ptarmigan has 23 recognized subspecies:

Nome scientifico

Lagopus muta

Autorità

(Montin, 1781)

Ordine

Galliformi

Famiglia

Phasianidae

Genere

Lagopo

Areale e habitat

The rock ptarmigan is a sedentary species which breeds across Arctic and Subarctic Eurasia and North America (including Greenland) on rocky mountainsides and tundra. It is widespread in the Arctic Cordillera and is found in isolated populations in the mountains of Norway, Sweden, Scotland, the Pyrenees, the Alps, Bulgaria, the Urals, the Pamir Mountains, the Altay Mountains, and Japan—where it occurs only in the Japanese Alps and on Mount Haku. Because of the remote habitat in which it lives, it has only a few predators—such as golden eagles—and it can be surprisingly approachable. It has been introduced to New Zealand, South Georgia, the Kerguelen Islands, and the Crozet Islands.<p>The small population living on Franz Josef Land in the Russian High Arctic overwinters during the polar night and survives by feeding on rich vegetation on and underneath high cliffs where seabird colonies are located in summer.<p>During the last ice age, the species was far more widespread in continental Europe.

Migrazione

Vertical migration

Comportamento

Food sources can vary tremendously depending on the region of their distribution. In Alaska, rock ptarmigans consume aspen buds, dwarf birch and willow buds and catkins as a staple winter diet. They transition their diets over to crowberries and lingonberry shrubs during the spring. The greatest variety in its diet occurs during early summer, when it feeds on willow leaves, as well as the leaves and flowers of Dryas and locoweed. It also feeds on berries, bistort seeds, and birch buds from late summer to autumn. Insects, larvae and snails are eaten by chicks.<p>Apart from the red eye combs, male rock ptarmigans have no 'distinct' plumage (other than the black eye stripe) that are more typical for other grouse in temperate regions. Studies on other grouses have shown that much variation in comb size and colour exists between the species, and that the comb is used in courtship display and aggressive interactions between males. Many studies have shown that there is a strong correlation between the comb size and the level of testosterone in males; one report from 1981 showed that the amount of testosterone is correlated to aggressiveness against other males.<p>The male's comb has been the focus of studies regarding sexual selection. Studies of a population of male rock ptarmigans in Scarpa Lake, Nunavut, have shown that during the first year, mating success among males was influenced by comb size and condition, and bigamous males had larger combs than monogamous males. The correlation to size disappeared after the first year, but the correlation to comb condition remained. This is consistent with another study of the same population of L. muta that showed that mating success overall is correlated to comb condition. Exceptions were first-time breeders, in which the size of the comb influenced mating success.<p>The rock ptarmigan becomes sexually mature at six months of age and commonly has up to six chicks. Because of this high breeding rate, the size of the population is affected very little by factors such as hunting.

Conservazione

Tendenza della popolazione

declining