Letter-winged Kite

识别特征

The adult letter-winged kite is about 35 cm (14 in) in length, with a wingspan between 84 and 100 cm (33 and 39 in). The female is slightly heavier, averaging 310 g (11 oz) compared to the male's average weight of 260 g (9.2 oz). The sexes have similar plumage. The adult male has pale grey upperparts, wings and nape with a white head and white underparts. It has large deep-red eyes, which are surrounded by a black eye patch. Its bill is black, with a dark grey-brown cere at its base. Its wings are marked with a black shoulder patch above and a striking black line underneath, which runs from the primary coverts to the body, and which resembles a letter 'M' or 'W' when flying. The central rectrices of the tail are pale grey, while the rest of the tail feathers are white. The legs and feet are a fleshy pinkish white or white. The feet have three toes facing forwards and one toe facing backwards. The female is similar but can be distinguished by a greyer crown, and its grey plumage is slightly darker all over. Moulting has been recorded from all months except May and August, and is probably related to breeding.<p>The juvenile has a white lower forehead, face, chin and throat, with a brownish orange band across the forehead, neck and breast. It has a similar dark eye patch to the adult, and the eyes themselves are dark brown. The hindneck is grey-brown, and the upperpart feathers are grey-brown with orange tips. The rump and central tail rectrices are pale grey tipped with orange. The bill is black with a brownish grey cere.<p>The letter-winged kite soars with v-shaped upcurved wings, the primaries slightly spread and the tail fanned, giving it a square appearance. When flying actively, it beats its wings more slowly and deeply than the black-shouldered kite (Elanus axillaris). The wing beats are interspersed with long glides on angled wings. It can also hover motionless facing into the wind and flapping its wings. The 'M' or 'W' on the underside of its wing and lack of black wing tips help distinguish it from the black-shouldered kite. Additionally, the latter species is diurnal, not nocturnal. At night, the letter-winged kite could be mistaken for the eastern barn owl (Tyto javanica) or eastern grass owl (T. longimembris), but these species have large heads; longer and trailing legs; blunted wings; and stockier bodies. The grey falcon (Falco hypoleucos) has somewhat similar colouration to the letter-winged kite but is bulkier and heavier overall, and lacks the black markings.<p>The letter-winged kite is generally silent when alone but often noisy when breeding or roosting communally at night, beginning to call at the rising of the moon. Its calls have been described as chicken-like chirping or a repeated loud kacking, and at times resemble those of the barn owl or black-shouldered kite. A rasping call, or scrape, composed of six or seven half-second long notes is the main contact call between a pair. It is often used by the female in answer to a whistle by her mate, when a bird alights at the nest, or—loudly—in response to an intruder. The male can utter a loud whistle in flight, which can serve as an alarm call. Mated pairs chatter to one another at night in the colony.

分类信息

The letter-winged kite was described by ornithologist John Gould in 1842 under its current binomial name Elanus scriptus. The specific epithet is from the Latin word scriptum, meaning "written" or "marked". British explorer Charles Sturt wrote of seeing them on his travels in his 1849 book Narrative of an Expedition into Central Australia. The letter-winged kite is monotypic: no subspecies are recognised, nor is there any recorded geographic variation. Molecular evidence shows that the letter-winged kite and its relatives belong to the subfamily Elaninae, an early offshoot within the raptor family Accipitridae. There is some evidence that they may be more divergent from other raptors and better placed in their own family.<p>"Letter-winged kite" has been designated as the official English-language name by the International Ornithologists' Union (IOU), derived from the letter-like markings under the wings. In Central Australia, southwest of Alice Springs, the Pitjantjatjara name for the letter-winged kite is nyanyitjira. It has been incorrectly called white-breasted sparrowhawk.

学名

Elanus scriptus

命名信息

Gould, 1842

目

Accipitriformes

科

Accipitridae

属

Elanus

分布与栖息地

The usual habitat of the letter-winged kite is arid and semi-arid open, shrubby or grassy country, across the arid interior of the continent, particularly the southern Northern Territory, particularly the Barkly Tableland, and northeastern South Australia, and Queensland, where it is relatively common in western areas south of 20° south, and has been recorded as far afield as Townsville and Stradbroke Island. In South Australia it may reach the Eyre Peninsula and southeastern corner on occasion. The species is generally rare in New South Wales: it has been recorded in the vicinity of Broken Hill in the far west, and twice in Inverell in the north of the state—once found dead in a street in 1965 and once spotted alive a year later. It is rare in Western Australia.<p>Its abundance or even presence in any given area is heavily dependent on availability of food; spells of significant rainfall inland lead to surges in rodent numbers, which in turn lead to irruptions of letter-winged kites. Nesting and raising multiple broods in succession, the kite population may increase ten-fold. Major irruptions have taken place in 1951–53, 1969–70, 1976–77, and 1993–95. Eventually dry conditions lead to a fall in rodent numbers and dispersal of birds, which often starve if they fail to find prey elsewhere.

迁徙

Nomadic

行为

Migration pattern: Nomadic.

保护状况

Population trend: stable.

种群趋势

stable