Red-tailed black cockatoo

Appearance

Red-tailed black cockatoos are around 60 centimetres in length and sexually dimorphic. The male's plumage is all black with a prominent black crest made up of elongated feathers from the forehead and crown. The bill is dark grey. The tail is also black with two lateral bright red panels. Females are black with yellow-orange stripes in the tail and chest, and yellow grading to red spots on the cheeks and wings. The bill is pale and horn-coloured. The underparts are barred with fine yellow over a black base. Male birds weigh between 670 and 920 grams, while females weigh slightly less at 615–870 grams. In common with other cockatoos and parrots, red-tailed black cockatoos have zygodactyl feet, two toes facing forward and two backward, that allow them to grasp objects with one foot while standing on the other, for feeding and manipulation. Black cockatoos are almost exclusively left-footed.

Juvenile red-tailed black cockatoos resemble females until puberty, which occurs around four years of age, but have paler yellow barred underparts. As the birds reach maturity, males gradually replace their yellow tail feathers with red ones; the complete process takes around four years.

Naming

The species complex was first described by the ornithologist John Latham in 1790 as "Psittacus banksii", commemorating English botanist Sir Joseph Banks. The red-tailed black cockatoo also has the distinction of being the first bird from Eastern Australia illustrated by a European, as a female, presumably collected at Endeavour River in north Queensland, was sketched by Banks' draughtsman Sydney Parkinson in 1770.

Distribution

The red-tailed black cockatoo principally occurs across the drier parts of Australia. It is widespread and abundant in a broad band across the northern half of the country, where it has been considered an agricultural pest, with more isolated distribution in the south. It is found in a wide variety of habitats, from shrublands and grasslands through eucalypt, sheoak and "Acacia" woodlands, to dense tropical rainforests. The bird is dependent on large, old eucalypts for nesting hollows, although the specific gums used vary in different parts of the country.

Cockatoos are not wholly migratory, but they do exhibit regular seasonal movements in different parts of Australia. In the northern parts of the Northern Territory, they largely leave areas of high humidity in the summer wet season. In other parts of the country cockatoo seasonal movements tend to follow food sources, a pattern recorded in Northern Queensland, and New South Wales. In southwest Western Australia, both extant subspecies appear to have a north-south pattern; northwards after breeding in the case of subspecies "naso", while movements by subspecies "samueli" in the wheatbelt can be irregular and unrelated to the seasons.

Behavior

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.

Reproduction

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. 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 deep and 0.25–0.5 metres wide, with a base of woodchips. A clutch consists of 1 to 2 white, lustreless eggs, although the second chick is in most cases neglected and perishes in infancy.

Food

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 woolybutt "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 nuts consumed are those of "Acacia", "Allocasuarina", "Banksia", "Grevillea" and "Hakea", as well as berries, fruits and various insects. Cockatoos have adapted to eating some introduced plants such as the doublegee. There is some evidence of consumption of wild radish, wild turnip and melon. Red-tailed black cockatoos have been implicated as agricultural pests of peanut and other crops at Lakeland Downs in Far North Queensland. Here the cockatoos, in flocks of up to several hundred birds, have learned to sever the peanut plants above ground level before pulling the peanuts out of the ground by their stems and shelling them. They also damage electrical cables on pivot irrigators.