Black-shouldered kite
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The black-shouldered kite (Elanus axillaris), also known as the Australian black-shouldered kite, is a small raptor found in open habitats throughout Australia. It resembles similar species found in Africa, Eurasia and North America, including the black-winged kite, a species that has in the past also been called "black-shouldered kite". Measuring around Template:Convert in length, with a wingspan of Template:Convert, the adult black-shouldered kite has predominantly grey-white plumage and prominent black markings above its red eyes. It gains its name from the black patches on its wings. The primary call is a clear whistle, uttered in flight and while hovering. It can be confused with the related letter-winged kite in Australia, which is distinguished by the striking black markings under its wings.
The species forms monogamous pairs, breeding between August and January. The birds engage in aerial courtship displays which involve high circling flight and ritualised feeding mid-air. Three or four eggs are laid and incubated for around thirty days. Chicks are fully fledged within five weeks of hatching and can hunt for mice within a week of leaving the nest. Juveniles disperse widely from their home territory. The black-shouldered kite hunts in open grasslands, searching for its prey by hovering and systematically scanning the ground. It mainly eats small rodents, particularly the introduced house mouse, and has benefitted from the modification of the Australian landscape by agriculture. It is rated as least concern on the International Union for Conservation of Nature (IUCN)'s Red List of Threatened Species.
Taxonomy
The black-shouldered kite was first described by English ornithologist John Latham in 1801, as Falco axillaris.<ref>Template:Cite book</ref> Its specific name is derived from the Latin axilla, meaning "armpit",<ref>Template:Cite book</ref> relating to the dark patches under the wings.<ref name=fraser13/> He reported the description came from a bird that had been kept for two months in the early colony.<ref>Template:Cite book</ref> The species description was based on one of four paintings by Australian painter Thomas Watling of a bird in the Sydney district in the 1790s.<ref name=mathews16/>
English naturalist John Gould described the same species as Elanus notatus in 1838 from a specimen from New South Wales,<ref>Template:Cite book</ref> apparently unaware of Latham's description.<ref name=mathews16>Template:Cite book</ref> English zoologist George Robert Gray followed Latham using the binomial Elanus axillaris in 1849.<ref>Template:Cite book</ref> Gould conceded Latham's name was valid and hence had precedence, and E. notatus was reduced to synonymy. Australian ornithologist Gregory Mathews argued that Latham's description mentioned black axillaries and hence must have referred to the letter-winged kite, and that Watling's drawings were inconclusive. He promoted the use of E. notatus over E. axillaris in 1916.<ref name=mathews16/> This was followed for many years.<ref name=hbw>Template:Cite journal</ref> But in 1980 Australian taxonomists Richard Schodde and Ian J. Mason refuted Mathews' claim that the original description of E. axillaris was ambiguous and reinstated the name.<ref>Template:Cite book</ref> This has been followed by subsequent authorities.<ref name=hbw/><ref name="ioclist"/> The black-shouldered kite has no recognised subspecies.<ref name="ioclist"/>
"Black-shouldered kite" has been designated the official English name by the International Ornithologists' Union (IOC).<ref name="ioclist">Template:Cite web</ref> It has also been called the Australian black-shouldered kite to distinguish it from the Eurasian black-winged kite (E. caeruleus) and American white-tailed kite (E. leucurus)—both formerly known as "black-shouldered kite".<ref name=fraser13>Template:Cite book</ref> Watling had recorded the Dharug term Geo-ga-rack.<ref name=mathews16/>
In 1959, American ornithologist Kenneth C. Parkes noted that the plumage of the black-shouldered kite is similar to that of the black-winged and white-tailed kites, and proposed that all three were subspecies of a single cosmopolitan species E. caeruleus—much like the peregrine falcon (Falco peregrinus).<ref name=Parkes/> Researchers William S. Clark and Richard C. Banks disputed this, pointing out the differences in anatomical proportions such as wing shape and tail length, and hunting behavior (E. caeruleus rarely hunts by hovering, unlike the other two species) and proposed the species be separated again in 1992.<ref name=Clark>Template:Cite journal</ref> They are regarded as distinct in the IOC World Bird List.<ref name="ioclist"/>
Molecular evidence shows that the black-shouldered kite and its relatives belong to a subfamily Elaninae that is an early offshoot within the raptor family Accipitridae.<ref name=lerner2005/><ref name=griffiths2007/> There is some evidence they are more divergent from other raptors and better placed in their own family.<ref name=Wink/><ref name=Ausraptors/>
Description
The adult black-shouldered kite is around Template:Convert in length, with a wingspan of between Template:Convert. The female is slightly heavier, weighing on average around Template:Convert compared to the male's average weight of Template:Convert. The sexes have similar plumage.Template:Sfn The crown, neck and upperparts are pale grey, while the head and underparts are white. A black comma-shaped marking lies in front of and stretches over and behind the eye, which is deep red and surrounded by a black orbital ring. The leading edge of the outer wing is black. When perched, this gives the species its prominent black "shoulders". The central rectrices of the tail are pale grey, while the rest of the tail feathers are white. The bill is short with a sharp, hooked tip to the upper mandible. Its nostrils and the cere are bright or dull yellow and the bill is black. The legs and feet are also yellow or golden-yellow,Template:Sfn and the feet have three toes facing forwards and one toe facing backwards.<ref name=backyardbirds/>
The juvenile has a white forehead and chin and rusty brown neck, nape and breast with darker streaks. The back and wings are mottled buff or brown. There is a less distinctive dark shoulder patch, but a larger comma-shaped patch over the eyes. The eyes themselves are dark brown. The bill is black with a horn-coloured cere.Template:Sfn
Black-shouldered kites spiral into the wind like a kestrel. They soar with V-shaped up-curved wings, the primaries slightly spread and the tail widely fanned,<ref name=Morcombe/> giving the tail a squarer appearance and visible 'fingers' on the wings.Template:Sfn In level flight progress is rather indirect.<ref name=Morris/> Their flight pattern has been described as 'winnowing' with soft steady beats interspersed with long glides on angled wings.<ref name=Raptors/> They can most often be seen hovering with wings curved and tail pointing down.Template:Sfn
The black-shouldered kite is very similar to the related letter-winged kite (E. scriptus), but has the black mark above and behind the eye, a white rather than grey crown, and shows all-white underparts in flight except for the black markings on the shoulder, dark wingtips,<ref name=Morcombe/> and a small black patch on the underwing.Template:Sfn It is slightly larger than the nankeen kestrel (Falco cenchroides).Template:Sfn The latter species lacks wing markings and has pale brown plumage.<ref name=DebusS/> It keeps its wings level when soaring, and has a faster wingbeat when hovering. The grey falcon (Falco hypoleucos) has somewhat similar coloration to the black-shouldered kite but is bulkier and heavier overall and lacks the black markings.Template:Sfn Its wings are barred, and it preys on birds. The grey goshawk (Accipiter novaehollandiae) has wider more rounded wings, underwing markings and glides with lowered wings.<ref name=DebusS/>
Vocalisations
The black-shouldered kite is generally silent, except in the breeding season when its calls, though weak, can be persistent.<ref name=Raptors/> It primarily utters a clear whistled chee, chee, chee call in flight and while hovering, or a hoarse wheezing skree-ah when perched.<ref name=Raptors/> A short high whistle is the primary contact call between a pair, while a harsh scraping call is the most common call used by the female and large young, and brooding females call to their young with a deep, soft, frog-like croak.<ref name=Hollands/>
A variety of different calls have been recorded from captive birds, including harsh, harmonic, chatter and whistle vocalisations. Harsh calls were made when a bird was alarmed or agitated, whistle-type calls were emitted in general contexts, sometimes monotonously, and shorter duration "chatter" calls were given when a bird sighted a human near the enclosure.<ref name=Jurisevic/>
Distribution and habitat
Black-shouldered kites may be sedentary or nomadic and are generally found in open grasslands or valleys where there are scattered clumps of trees, where the grass or groundcover is accessible from the air and ranges from 30 cm to 1.5 m (1–5 ft) high. As well as native grasslands they forage over pastures, cereal or vegetable crops and vineyards, often focusing on areas that have been recently harvested or ploughed and hence rendering prey more exposed. In urban areas, they are encountered on the edge of towns on wasteland, irregularly mown areas, sports fields, golf courses or grassy roadside verges.Template:Sfn They also hunt over coastal dunes and drier marshland,<ref name=Raptors/> but avoid areas with dense cover such as forest as well as bare or rocky ground.Template:Sfn
Their numbers fluctuate during drought and floods and can be irruptive in response to sudden increases in mouse populations.<ref name=Raptors/> The most distant banding recovery was from the Red Banks area in South Australia to Lithgow in eastern New South Wales three and a half years later, a distance of Template:Convert.<ref>Template:Cite web</ref>
Although reported throughout Australia, they are most common in the relatively fertile south-east and south-west corners of the mainland, and in south-east Queensland. They are rare in the deep desert and dryer areas such as western Cape York or the Northern Territory, and are occasional visitors to northern Tasmania,Template:Sfn King Island,<ref>Template:Cite journal</ref> and the Torres Strait islands.Template:Sfn
Behaviour
Black-shouldered kites usually hunt singly or in pairs, though where food is plentiful they occur in small family groups and can be loosely gregarious at times of irruptions, with up to 70 birds reported feeding together during a mouse plague.<ref name=Raptors/> They roost communally, like other Elanus species.<ref name=GRIN/> They are territorial when food is not abundant. The practice of "tail flicking" where, on landing, the tail is flicked up and lowered and the movement repeated persistently is thought to be a possible territorial display.<ref name=Raptors/>
Breeding
Aerial courtship displays involve single and mutual high circling flight, and the male may fly around with wings held high rapidly fluttering, known as flutter-flight.Template:Sfn Courting males dive at the female, feeding her in mid-flight. The female grabs food from the male's talons with hers while flipping upside-down. They may lock talons and tumble downwards in a ritualised version of grappling, but release just before landing.<ref name=Curtis/> All courtship displays are accompanied by constant calling.<ref name=Raptors/>
Black-shouldered kites form monogamous pairs. The breeding season is usually August to January, but is responsive to mice populations,<ref name=Raptors/> and some pairs breed twice in a good season.<ref name=DebusS/> Both sexes collect material for the nest but the female alone builds it.Template:Sfn A large untidy shallow cup of sticks usually in the foliage near the top of trees, the nest takes anywhere from two to six weeks to be built.Template:Sfn It is constructed of thin twigs and is around Template:Convert across when newly built, but growing to around Template:Convert across and Template:Convert deep after repeated use.<ref name=Raptors/> The nest is lined with green leaves and felted fur, though linings of grass and cow dung have also been reported.<ref name=Raptors/> It is generally located in the canopy of an isolated or exposed tree in open country, elevated Template:Convert or more above the ground. Black-shouldered kites have been known to use old Australian magpie, crow or raven nests.<ref name=Beru03/>
Females perform most of the care of eggs and nestlings, though males take a minor share of incubation and brooding.<ref name =Debus/> The clutch consists of three to four dull white eggs of a tapered oval shape measuring Template:Convert and with red-brown blotches that are often heavier around the larger end of the egg.<ref name=Beru03/> The eggs are laid at intervals of two to five days.Template:Sfn The female incubates the eggs for 30 days and when the eggs hatch the chicks are helpless but have soft down covering their body. For the first two weeks or so the female broods the chicks constantly, both day and night. She does no hunting at all for the first three weeks after hatching, but calls to the male from the nest, and he generally responds by bringing food.<ref name=Cupper/> The female feeds the chicks with the mice brought back to the nest by the male,<ref name=backyardbirds/> feeding them in tiny pieces for the first week or two, at which time the chicks are capable of swallowing a mouse whole.<ref name=Cupper/> The nestling period lasts around 36 days, and the post-fledging period at least 36 days with parental feeding for at least 22 days.<ref name=Debus/> When the chicks are older both parents take it in turns to feed them. Black feathers start to appear along the chicks' wings when they are about a fortnight old, and they are fully fledged and are ready to fly in five weeks.<ref name=backyardbirds/> Within a week of leaving the nest the young birds are capable of hunting for mice on their own.<ref name=Hollands/>
Juveniles disperse widely, taking up territory that can be as far as Template:Convert from the nest site.<ref name=DebusS/>
Food and hunting
The black-shouldered kite has become a specialist predator of the introduced house mouse, often following outbreaks of mouse plagues in rural areas.<ref name=Sinclair/> It takes other suitably-sized creatures when available, including grasshoppers, rats, small reptiles, birds, and even (very rarely) rabbits, but mice and other mouse-sized mammals account for over 90% of its diet. Its influence on mouse populations is probably significant; adults take two or three mice a day each if they can,<ref name=Sinclair/> around a thousand mice a year.<ref name=Hollands/> On one occasion, a male was observed bringing no less than 14 mice to a nest of well-advanced fledglings within an hour.<ref name=Debus/> In another study, a female kite was seen to struggle back to fledglings in the nest with a three-quarters grown rabbit, a heavy load for such a small bird.<ref name=Cupper/>
Like other elanid kites, the black-shouldered kite hunts by quartering grasslands for small creatures. This can be from a perch, but more often by hovering in mid-air.<ref name=Raptors/> It is diurnal, preferring to hunt during the day, particularly in the early morning and mid to late afternoon, and occasionally hunts in pairs. Its hunting pattern, outside breeding periods and periods of abundant prey, has distinct crepuscular peaks, perhaps corresponding to mouse activity.<ref name=Morris/> When hunting, the kite hovers with its body hanging almost vertically, and its head into the wind.<ref name=Cupper/> Unlike the nankeen kestrel, the black-winged kite shows no obvious sideways movement, even in a strong breeze.<ref name=Cupper/> One study of a nesting pair noted that the male searched aerially for 82% of the search time.<ref name=Debus/> Typically, a kite hovers Template:Convert above a particular spot, peering down intently, sometimes for only a few seconds, often for a minute or more, then glides swiftly to a new vantage point and hovers again.<ref name=Morris/> When hunting from a perch, a dead tree is the preferred platform. Like other Elanus kites, the black-shouldered kite grips a vertical branch with a foot on either side, each one above the other and turned inwards, which enables them to maintain a secure footing on relatively small branches.<ref name=Hollands/> Though hovering is the most common hunting method, the kites have been observed searching the ground beneath a vantage point for periods of up to an hour.<ref name=Hollands/>
When a mouse or other prey is spotted, the kite drops silently onto it, feet-first with wings raised high; sometimes in one long drop to ground level, more often in two or more stages, with hovering pauses at intermediate heights. Prey is seized in the talons and about 75% of attacks are successful.<ref name=Debus/> Prey can either be eaten in flight or carried back to a perch. Birds will have a favoured feeding perch, beneath which accumulate piles of pellets or castings.<ref name=Morris/>
Conservation status
The arrival of Europeans to Australia has, on the whole, benefited the black-shouldered kite through land clearing, irrigation for agriculture, grain harvesting, and storage practices which provide suitable conditions for much larger numbers of mice.<ref name=backyardbirds/> As the species has a large range and an increasing population, it is listed as "Least Concern" on the IUCN Red List of Threatened species.<ref name="iucn status 13 November 2021" /><ref name=BirdLife/> In southwestern Australia, it has become one of the most commonly recorded raptors in the wheatbelt.<ref name=GRIN/> According to raptor researcher Stephen Debus, this species did not suffer from eggshell thinning during the period of DDT use in Australia, though he believes secondary poisoning is possible from rodenticides used during mouse plagues or from pesticides used during locust plagues.<ref name=GRIN/> Populations in areas with high sheep and rabbit numbers may decline, as these animals compact the soil and reduce the available habitat for mice.<ref name=backyardbirds/>