Kea

Identificazione

The kea is a large parrot measuring 46 to 50 cm (18 to 20 in) in total length, with some specimens possibly reaching 55 cm (22 in). Adult kea weigh between 750 and 1,000 g (1.65 and 2.20 lb), with males averaging 956 g (2.108 lb) and females averaging 779 g (1.717 lb). One source listed the mean adult weight as 922 g (2.033 lb) It has mostly olive-green plumage with a grey beak having a long, narrow, curved upper beak. The adult has dark-brown irises, and the cere, eyerings, and legs are grey. It has orange feathers on the undersides of its wings. The feathers on the sides of its face are dark olive-brown, the ones on its back and rump are orange-red, and some of the outer wing feathers are dull blue. It has a short, broad, bluish-green tail with a black tip. Feather shafts project at the tip of the tail and the undersides of the inner tail feathers have yellow-orange transverse stripes. The male is about 5% longer than the female, and the male's upper beak is 12–14% longer than the female's. Juveniles generally resemble adults, but have yellow eyerings and cere, an orange-yellow lower beak, and grey-yellow legs.

Tassonomia

The kea was described by ornithologist John Gould in 1856, from two specimens shown to him by Walter Mantell. Some elderly Māori had told Mantell about the bird around eight years previously and how it used to visit the coast in winter but had not been seen in recent times. Mantell investigated and obtained the birds in Murihiku. Its specific epithet, the Latin term notabilis, means "noteworthy". The common name kea is from Māori, probably an onomatopoeic representation of their in-flight call – 'keee aaa'. The word "kea" is both singular and plural.<p>The genus Nestor contains four species: the New Zealand kākā (Nestor meridionalis), the kea (N. notabilis), the extinct Norfolk kākā (N. productus), and the extinct Chatham kākā (N. chathamensis). All four are thought to stem from a "proto-kākā", dwelling in the forests of New Zealand five million years ago. Their closest relative is the flightless kākāpō (Strigops habroptilus). Together, they form the parrot superfamily Strigopoidea, an ancient group that split off from all other Psittacidae before their radiation.

Nome scientifico

Nestor notabilis

Autorità

Gould, 1856

Ordine

Psittaciformi

Famiglia

Strigopidae

Genere

Nestor

Areale e habitat

The kea is one of nine living endemic parrot species in New Zealand.<p>The kea ranges from lowland river valleys and coastal forests of the South Island's west coast up to alpine regions of the South Island such as Arthur's Pass and Aoraki / Mount Cook National Park. It is closely associated throughout its range with the southern beech (Nothofagus) forests in the alpine ridge.<p>Apart from occasional vagrants, kea today are not found in the North Island. Subfossil kea bones have been found in sand dunes at Mataikona in the eastern Wairarapa, Poukawa near Hastings, and Waitomo, indicating that they ranged through lowland forest over much of the North Island until the arrival of Polynesian settlers about 750 years ago. Kea subfossils are not restricted to alpine areas, being commonly found in lowland or coastal sites in the South Island. The current distribution of kea reflects the effects of mammalian predators, including humans, which have driven them out of lowland forests into the mountains.

Migrazione

Resident species

Comportamento

At least one observer has reported that the kea is polygynous, with one male attached to multiple females. The same source also noted that there was a surplus of females.<p>Kea are social and live in groups of up to 13 birds. Isolated individuals do badly in captivity, but respond well to seeing themselves in a mirror.<p>In one study, nest sites occur at a density of one per 4.4 square kilometres (1.7 sq mi). The breeding areas are most commonly in southern beech (Nothofagus) forests, located on steep mountainsides. Breeding at heights of 1,600 metres (5,200 ft) above sea level and higher, it is one of the few parrot species in the world to regularly spend time above the tree line. Nest sites are usually positioned on the ground underneath large beech trees, in rock crevices, or dug burrows between roots. They are accessed by tunnels leading back 1 to 6 metres (3.3 to 19.7 ft) into a larger chamber, which is furnished with lichens, moss, ferns, and rotting wood. The laying period starts in July and reaches into January. Two to five white eggs are laid, with an incubation time of around 21 days, and a brooding period of 94 days.<p>Mortality is high among young kea, with less than 40% surviving their first year. The median lifespan of a wild subadult kea has been estimated at five years, based on the proportion of kea seen again in successive seasons in Arthur's Pass, and allowing for some emigration to surrounding areas. Around 10% of the local kea population were expected to be over 20 years of age. The oldest known captive kea was 50 years old in 2008.<p>An omnivore, the kea feeds on more than 40 plant species, beetle larvae, grasshoppers, land snails, other birds (including shearwater chicks), and mammals (including sheep, rabbits and mice). It has been observed breaking open shearwater nests to feed on the chicks after hearing the chicks in their nests. It enjoys the flesh and bone marrow from carcasses. The kea has also taken advantage of human garbage and "gifts" of food.<p>Tool use behavior has been observed in this species, wherein a bird named Bruce, who has a broken upper beak, wedged pebbles between his tongue and lower mandible and then utilized this arrangement to aid with his preening habits.<p>The controversy about whether the kea preys on sheep is long-running. Sheep suffering from unusual wounds on their sides or loins were noticed by the mid-1860s, within a decade of sheep farmers moving into the high country. Although some supposed the cause was a new disease, suspicion soon fell on the kea. James MacDonald, head shepherd at Wanaka Station, witnessed a kea attacking a sheep in 1868, and similar accounts were widespread. Prominent members of the scientific community accepted that kea attacked sheep, with Alfred Wallace citing this as an example of behavioural change in his 1889 book Darwinism. Thomas Potts noted that attacks were most frequent during winter and snow-bound sheep with two years growth in their fleece were the most vulnerable, while newly-shorn sheep in warm weather were rarely molested. Despite substantial anecdotal evidence of these attacks, others remained unconvinced, especially in later years. For instance, in 1962, animal specialist J.R. Jackson concluded, while the bird may attack sick or injured sheep, especially if it mistook them for dead, it was not a significant predator. In August 1992, however, its nocturnal assaults were captured on video, proving that at least some kea will attack and feed on healthy sheep. The video confirmed what many scientists had long suspected: that the kea uses its powerful, curved beak and claws to rip through the layer of wool and eat the fat from the back of the animal. Though the bird does not directly kill the sheep, death can result from infections or accidents suffered by animals when trying to escape.<p>Since kea are now a protected species, their depredations are generally tolerated by sheep farmers, though why some kea attack sheep, and others do not, remains unclear. Various theories, including similarities with existing food sources, curiosity, entertainment, hunger, maggots as well as a progression from scavenging dead sheep and hides have all been put forward as to how the behaviour was first acquired. Anecdotal evidence also suggests only particular birds have learned the behaviour, with identification and removal of those individuals being sufficient to control the problem.<p>There are also anecdotal reports of kea attacking rabbits, dogs, and even horses. There are also suggestions that kea used to feed on moa in a similar way.

Conservazione

Tendenza della popolazione

declining