Ghiandaia di Steller

Identificazione

Steller's jay is about 30–34 cm (12–13 in) long and weighs about 100–140 g (3.5–4.9 oz). Steller's jay shows a great deal of regional variation throughout its range. Blackish-brown-headed birds from the north gradually become bluer-headed farther south. Steller's jay has a more slender bill and longer legs than the blue jay and, in northern populations, has a much more pronounced crest.: 69  It is also somewhat larger.<p>The head is blackish-brown, black, or dark blue, depending on the subspecies of the bird, with lighter streaks on the forehead. This dark coloring gives way from the shoulders and lower breast to silvery blue. The primaries and tail are a rich blue with darker barring. Birds in the eastern part of its range along the Great Divide have white markings on the head, especially over the eyes; birds further west have light blue markers and birds in the far west along the Pacific Coast have small, very faint, or no white or light markings at all.

Tassonomia

Steller's jay was formally described in 1788 by the German naturalist Johann Friedrich Gmelin in his revised and expanded edition of Carl Linnaeus's Systema Naturae. He placed it with the crows in the genus Corvus and coined the binomial name Corvus stelleri. Gmelin based his account on "Stellers crow" that had been described in 1781 by the English ornithologist John Latham in his book A General Synopsis of Birds. Latham had examined a specimen belonging to the naturalist Joseph Banks that had been collected in Nootka Sound, Vancouver Island off the Pacific coast of Canada. The specimen was one of the birds collected on Captain James Cook's third voyage to the Pacific Ocean. During this voyage Cook visited Nootka Sound from 29 March until 26 Apr 1778. Steller's jay is now placed with the blue jay in the genus Cyanocitta that was introduced in 1845 by the English ornithologist Hugh Strickland.<p>The bird is named after the German naturalist Georg Wilhelm Steller, the first European to record them, in 1741.<p>Thirteen subspecies are recognised:

Nome scientifico

Cyanocitta stelleri

Autorità

(Gmelin, JF, 1788)

Ordine

Passeriformi

Famiglia

Corvidi

Genere

Cyanocitta

Areale e habitat

Steller's jay occurs in most of the forested areas of western North America as far east as the eastern foothills of the Rocky Mountains from southern Alaska in the north to northern Nicaragua in the south completely replacing the blue jay prevalent on the rest of the continent in those areas. Its density is lower in the central Rocky Mountain region (Montana, Idaho, Wyoming and eastern Utah) plus the desert or scrubland areas of the Great Basin (e.g. Nevada, western Utah, southern Arizona and parts of California). Some hybridization with the blue jay in eastern foothills of the Rocky Mountains, especially Colorado, has been reported. It is also found in Mexico occurring through the interior highlands in northwestern Mexico as well as patchy populations in the rest of Mexico. In the northern end of its range it appears to be spreading from coastal Southeast Alaska across the Coast Mountains into southern Yukon Territory.<p>Steller's jay is also found in Mexico's interior highlands from Chihuahua and Sonora in the northwest southward to Jalisco, as well as other patchy populations found throughout Mexico. It is also found in south-central Guatemala, northern El Salvador, Honduras and Nicaragua.<p>Although Steller's jay primarily lives in coniferous forests, it can be found in other types of forests as well. They can be found from low to moderate elevations, and on rare occasions to as high as the tree line. Steller's jays are common in residential and agricultural areas with nearby forests.

Migrazione

Resident species

Conservazione

Tendenza della popolazione

rising