Oca di Hutchins

Identificazione

The black head and neck with white "chinstrap" distinguish this goose from all other geese except the larger Canada goose (Branta canadensis) and the similarly sized barnacle goose (B. leucopsis). There are up to five subspecies of cackling goose of varying sizes and plumage details. The female looks virtually identical but is slightly lighter and has a different voice. Some are hard to distinguish from the Canada goose, with which the cackling goose was long assumed to form one species, the cackling goose and the smaller Canada goose subspecies being called the lesser Canada goose. The smallest 1.4 kg (3.1 lb) cackling geese (B. h. minima) are much smaller than any Canada goose, but the subspecies B. h. hutchinsii, at up to 3 kg (6.6 lb), grows to the same size as some Canada geese. The distinctness of the extinct population of the Komandorski and Kuril Islands B. h. asiatica is controversial. The barnacle goose differs in having a black breast and grey, rather than brownish, body plumage.<p>Measurements:

Tassonomia

The genus name Branta is a Latinised form of Old Norse Brandgás, "burnt (black) goose", and the specific epithet hutchinsii commemorates English surgeon Thomas Hutchins who was employed by the Hudson's Bay Company.<p>The cackling goose was originally considered to be the same species or a subspecies of the Canada goose, but in July 2004 the American Ornithologists' Union's (AOU) Committee on Classification and Nomenclature split the two into two species, making cackling goose into a full species with the scientific name Branta hutchinsii. The British Ornithologists' Union (BOU) followed suit in June 2005.<p>The AOU has divided the many associated subspecies between both animals. To the present species were assigned:<p>The distinctions between the two geese have led to a great deal of confusion and debate among ornithologists. This has been aggravated by the overlap between the small types of Canada goose and larger types of cackling goose. The old "lesser Canada geese" were believed to be a partly hybrid population, with the birds named taverneri considered a mixture of minima with subspecies occidentalis and parvipes, which today remain with the Canada goose proper. Actually however, taverneri is one of the larger subspecies of cackling geese. In addition, it has been determined that the barnacle goose (B. leucopsis) is a derivative of the cackling goose lineage, whereas the Hawaiian goose (B. sandvicensis) is an insular representative of the Canada goose.<p>In the wake of the discussion generated by the official standalone species designation, introduced by the AOU and BOU in 2004 and 2005, Harold C. Hanson published a paper in 2007 suggesting that Canada and cackling geese should be split into six species and 200 subspecies. The radical nature of this proposal provoked surprise, with Richard Banks of the AOU urging caution before any of Hanson's proposals be accepted. No further redesignation has been introduced by either of these Ornithologists' Unions.

Nome scientifico

Branta hutchinsii

Autorità

(Richardson, 1832)

Ordine

Anseriformi

Famiglia

Anatidae

Genere

Branta

Areale e habitat

This species is native to North America, breeding in Northern Canada and Alaska in a variety of tundra habitats, where the nest is usually located in an elevated area near water. The eggs are laid in a shallow depression, lined with plant materials and down. However, as the nests are made close-to, or directly on, the ground, the eggs (along with lone nesting females and newly-hatched goslings) are particularly vulnerable to predation by certain mammalian carnivores. Depending on the region, potential threats may vary from free-ranging domestic or feral cats and dogs, to foxes, coyotes, rats and other animals, such as some species of snakes. Thus, as a result, both geese—especially the male—in a nesting pair become highly aggressive and defensive of the nesting site, even chasing people away who may happen to walk by.<p>A pair may mate for life (up to around 20 years). Adult geese are often seen leading their goslings in a line with one parent at the front, and the other at the back of the "parade".<p>Like most geese, the cackling goose is naturally migratory, with their overwintering range being most of the U.S. (locally in Western Canada, the West Coast of the U.S. and northern Mexico). The calls overheard from large flocks of cackling geese, flying in their typical "V"-shaped formation, signal the transitions into spring and fall. In some areas, migration routes change due to shifts in available habitat, environment and food sources.<p>As vagrants, cackling geese have reached Western Europe of their own accord, as has been proven by ringing recoveries and documented sightings. The birds seen in Europe are of, at least, the subspecies hutchinsii, and possibly others. Cackling geese are also found, naturally, as vagrants around the Kamchatka Peninsula in Far Eastern Russia (Siberia), East China, and throughout the islands of Japan. Nevertheless, the IUCN considered the species to be extirpated from Japan, where it previously had an established non breeding (winter) population. Birds have recently been reintroduced to both Japan and Siberia.

Areale riproduttivo

NA : c Canada

Areale non riproduttivo

to Texas and n Mexico

Migrazione

Complete migrants

Conservazione

Tendenza della popolazione

rising