The Black-shouldered Kite (Elanus axillaris) is a common small raptor found in open habitat throughout Australia.
It is easily recognised: a small white raptor with black-tipped wings, usually seen hovering over crops or grassland. It can be mistaken for an oversized Silver Gull — both have long, slim wings with darker tips — but only on first glance. If the hovering raptor is small and tan or brown coloured, then it will be a Nankeen Kestrel. The larger Brown Falcon also hovers from time to time, but rarely without a moderate breeze to assist, and never with the same precise control. The Black-shouldered Kite's close relative, the rare nocturnal Letter-winged Kite is not usually sighted far beyond the channels of the northern Lake Eyre Basin.
Black-shouldered Kites live almost exclusively on mice. They take 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 their diet. Their influence on mouse populations is probably significant: adults take two or three mice a day each if they can, and on one occasion a male was observed bringing no less than 14 mice to a nest of well-advanced fledglings within an hour.
Like other elanid kites, Black-shouldered Kites hunt by quartering grasslands for small creatures. This can be from a perch (usually a dead tree), but more often by hovering in mid-air with conspicuous skill and little apparent effort. Typically, a kite will hover 10 to 30 metres above a particular spot, peering down intently, sometimes for only a few seconds, often for a minute or more, then glide swiftly to a new vantage point and hover again.
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. About two-thirds of attacks are successful. Prey can either be eaten in flight or carried back to a perch.
Black-Shouldered Kites are around 35 to 38 cm in length and have a wingspan of between 80 and 95 cm. Adults are a very pale grey with a white head and white underparts. The leading edge of the inner wing is black. When perched, this gives them their prominent black "shoulders".
Black-shoulderd Kites have been reported from all parts of mainland Australia, but are most common in the south and east, in the south-west corner of Western Australia, and in the far north-west. They are rare in the deep desert and appear to be only accidental visitors to northern Tasmania and the Torres Strait islands.
Although also found in timbered country, they are mainly birds of the grasslands. European occupation of Australia has, on the whole, benefited them by clearing vast expanses of forest for agriculture and providing suitable conditions for much larger numbers of mice.
In the south and east, pairs tend to breed in spring, but also in autumn if the year is good. If the food supply is ample, breeding can be at any time of year and near-continuous. Both birds cooperate to build an untidy shallow cup nest of sticks, and line it with greenery, bark, and fur; the male usually bringing the material for the female to work with. The usual clutch size is three or four; the female broods and feeds the hatchlings while the male stands guard and hunts.
In good years, Black-shouldered Kites can multiply rapidly, then disperse to other areas when the food supply runs short. It is common in a given area to see only a few birds for a time then, a season or a couple of years later, to see large numbers. It is not clear to what extent these fluctuations are the result of birds arriving or departing as opposed to overall population increases and decreases.
The Black-shouldered Kite was formerly classified as the Australian race of a single near-worldwide species, found in Europe, Africa, and North America as well as Australia. The name Black-shouldered Kite was applied to all. Modern authorities regard the group as a complex of three related but separate species: the Australian Black-shouldered Kite (Elanus axillaris), the European and African Black-winged Kite (Elanus caeruleus) and the North American White-tailed Kite (Elanus leucurus).