naso, while movements by subspecies samueli in the wheatbelt can be irregular and unrelated to the seasons. Behaviour Red-tailed black cockatoos are diurnal, raucous and noisy, and are often seen flying high overhead in small flocks, sometimes mixed with other cockatoos. Flocks of up to 500 birds are generally only seen in the north or when the birds are concentrated at some food source. Otherwise, they are generally rather shy of humans. In northern and central Australia, birds may feed on the ground, while the two southern subspecies, graptogyne and naso, are almost exclusively arboreal. They tend to fly rather slowly with intermittent deep flapping wingbeats, markedly different from the shallow wingbeats of the similar glossy black cockatoo. They also often fly at considerable height. Breeding The male red-tailed black cockatoo courts by puffing up crest and cheek feathers, and hiding the beak; it then sings and struts, ending in a jump and a flash of red tail feathers toward the female who will most often reply by defensively biting him. Breeding generally takes place from May to September except in the case of the South-eastern subspecies, which nests during summer (December to February). Pairs of the subspecies samueli in the Wheatbelt region of Western Australia may produce two broods, while those of South-eastern subspecies only produce one. Nesting takes place in large vertical tree hollows of tall trees. Isolated trees are generally chosen, so birds can fly to and from them relatively unhindered. The same tree may be used for many years. Hollows can be 1 to 2 metres (3–7 ft) deep and 0.25–0.5 metres (10–20 in) wide, with a base of woodchips. A clutch consists of one or two white, lustreless eggs, although the second chick is in most cases neglected and perishes in infancy. Feeding Although red-tailed black cockatoos feed on a wide variety of native and introduced grains, the mainstay of their diet is eucalyptus seeds. There is a specific relationship between the species and larger-fruited species of gums. These vary across Australia but include the marri in Southwest Western Australia, Darwin woollybutt E. miniata across the north of the country, E. baxteri in Victoria and the bloodwood species Corymbia polycarpa and C. intermedia in Queensland. Cockatoos bite off branchlets with clusters of seed capsules, then hold them with their feet while chewing and harvesting seeds before littering the ground with debris. Among other seeds and