The letter-winged kite (Elanus scriptus) is a small, rare and irruptive bird of prey that is found only in Australia.

[2] The species begins breeding in response to rodent outbreaks, with pairs nesting in loose colonies of up to 50 birds each.

[4] British explorer Charles Sturt wrote of seeing them on his travels in his 1849 book Narrative of an Expedition into Central Australia.

[7] Molecular evidence shows that the letter-winged kite and its relatives belong to the subfamily Elaninae, an early offshoot within the raptor family Accipitridae.

[10][11] "Letter-winged kite" has been designated as the official English-language name by the International Ornithologists' Union (IOU),[6] derived from the letter-like markings under the wings.

[14] The letter-winged kite soars with v-shaped upcurved wings, the primaries slightly spread and the tail fanned, giving it a square appearance.

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.

[18] 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.

[19] Its calls have been described as chicken-like chirping or a repeated loud kacking,[16] and at times resemble those of the barn owl or black-shouldered kite.

The species is generally rare in New South Wales:[18] it has been recorded in the vicinity of Broken Hill in the far west,[20] 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.

[23] Eventually dry conditions lead to a fall in rodent numbers and dispersal of birds, which often starve if they fail to find prey elsewhere.

[18] The letter-winged kite typically hunts at night, with daytime foraging taking place in areas of superabundant or scarce prey.

[18] By day, birds roost in leafy trees with plenty of cover, in colonies of up to 400 individuals, becoming active at dusk.

[18] Their social behaviour is poorly known on account of their nocturnal habits and shy nature, being difficult to approach when roosting.

[19] Within its range, the letter-winged kite generally breeds in an area covering the Diamantina and Lake Eyre drainage basins, Sturt Stony Desert, eastern Simpson Desert and Barkly Tableland, to Richmond, Queensland, and Banka Banka Station in the north and Boolkarie Creek, South Australia, in the south.

[24] There does not appear to be a set breeding season; instead, the species forms nesting colonies in response to rodent irruptions.

Other species used include waddy (Acacia peuce), coolibah (Eucalyptus microtheca) and sheoaks (Casuarina spp.).

The nest is a large, untidy and shallow cup of sticks, usually located in the foliage near the top of trees, some five metres (15 ft) or higher off the ground.

[15] One Central Australian study over two and a half years found that, within six months of an outbreak starting, the birds had relocated to that location.

[27] When the rodent populations decline, the now superabundant kites may disperse and appear in coastal areas far from their normal range; though they may occasionally breed in these new locations, they do not persist and eventually disappear.

[15] Across Central Australia, the letter-winged kite shares its habitat with other nocturnal rodent hunters, the eastern barn owl and eastern grass owl; the former species prefers larger rodents such as the plains rat (Pseudomys australis), whereas the kite hunts all species, including the sandy inland mouse (Pseudomys hermannsburgensis) and spinifex hopping mouse (Notomys alexis), on availability.

[22] It is unknown to what extent competition for food with the introduced red fox or feral cat,[27] or if habitat degraded by overgrazing, have an impact on the letter-winged kite.