The birds engage in aerial courtship displays which involve high circling flight and ritualised feeding mid-air.

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.

[5] 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.

[6] English naturalist John Gould described the same species as Elanus notatus in 1838 from a specimen from New South Wales,[7] apparently unaware of Latham's description.

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.

[9] 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.

[11] 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.

[20] The juvenile has a white forehead and chin and rusty brown neck, nape and breast with darker streaks.

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.

[25] A variety of different calls have been recorded from captive birds, including harsh, harmonic, chatter and whistle vocalisations.

[26] 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.

[19] They also hunt over coastal dunes and drier marshland,[23] but avoid areas with dense cover such as forest as well as bare or rocky ground.

[28] 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.

[33] 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.

[23] It is generally located in the canopy of an isolated or exposed tree in open country, elevated 5 to 20 m (16 to 66 ft) or more above the ground.

[35] Females perform most of the care of eggs and nestlings, though males take a minor share of incubation and brooding.

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.

[39] 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.

[36] 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.

[38] Unlike the nankeen kestrel, the black-winged kite shows no obvious sideways movement, even in a strong breeze.

[25] 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.

[22] 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.

[30] Populations in areas with high sheep and rabbit numbers may decline, as these animals compact the soil and reduce the available habitat for mice.