horn-coloured. The underparts are barred with fine yellow over a black base. Male birds weigh between 670 and 920 grams (1.5–2 lb), while females weigh slightly less at 615–870 grams (1.25–1.75 lb). 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 (along with nearly all other cockatoos and most parrots). 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. As with other cockatoos, the red-tailed black cockatoo can be very long-lived in captivity; in 1938, ornithologist Neville Cayley reported one over fifty years old at Taronga Zoo. Another bird residing at London and Rotterdam Zoos was 45 years and 5 months of age when it died in 1979. Several calls of red-tailed black cockatoos have been recorded. The bird's contact call is a rolling metallic krur-rr or kree, which may carry long distances and is always given while flying; its alarm call is sharp. Displaying males vocalize a sequence of soft growling followed by a repetitive kred-kred-kred-kred. Distribution and habitat 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