Forest Red-tailed Black Cockatoo

Written by Ron Johnstone

Wednesday, 18 February 2009 09:38

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Known by the Noongar people as "Karrak", this spectacular cockatoo was named Calyptorhynchus banksii naso by John Gould in 1837; the name naso refers to the nose in reference to the large bill in comparison to other populations of Red-tailed Black Cockatoo. There are three subspecies, or different populations, of Red-tailed Black Cockatoo in Western Australia; Calyptorhynchus banksii macrorhynchus found in the Kimberley, C. b. samueli found in the arid zone (Pilbara, Gascoyne and northern Wheatbelt), and C. b. naso restricted, or endemic, to the Jarrah, Marri and Karri forests in the south-west corner of the State. Only naso the forest form is listed as Vulnerable as its overall distribution and population have declined greatly over the past 50 years.

Red-tailed Black Cockatoos have strong sexual dimorphism (sexual differences). The male is glossy black except for a bright red band towards the tip of the tail and it has a blackish bill. The female is mostly black with the head and wings spotted with pale yellow, the breast and belly barred with orange-yellow, the tail narrowly barred with orange-yellow and black and the bill greyish white. Juvenile and immature birds are similar to the female and adult plumage is acquired at four years of age. These birds live for about 50 years, begin breeding at four years of age, mate for life and tend to nest in the same hollow each breeding season (generally every 2 years). In many hills areas the cockatoos you see are from an ageing population with little recruitment back into the flock. Despite these being large conspicuous birds, very little is known about their breeding biology.

The male (L) is glossy black with a bright red panel in the tail.

The female (R) has orange-yellow barring on the breast and undertail.

The loud grating "kar-rak" call is very distinctive and carries for some distance.

They breed in large chimney-stack type hollows of mainly Marri, but also Jarrah, Karri, Wandoo and Bullich trees. The single egg is laid on woodchips at the bottom of the hollow and only the female incubates and broods the chick. She leaves the nest once or twice a day to be fed by the male.

Over the past 10 years the WA Museum has been studying the breeding biology of the Forest Red-tailed Black Cockatoo C. b. naso in the Perth hills slowly gaining knowledge of their nesting areas, nest sites, breeding behaviour and timing of nesting attempts. Their local movements from the hills onto parts of the Swan Coastal Plain and their food and social organisation have also been studied over this period. There has been a dynamic change in their foraging ecology over this time with flocks now moving well out onto the coastal plain almost to the coast.

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Research on growth rates of nestlings.

Note yellow band on right leg of chick (from research nest tree 044).

Our studies have shown that hollows suitable for these large cockatoos do not begin to appear in eucalypts until they are at least 230 years old. It is now very evident that the loss or decrease in ancient veteran and stag hollow-bearing trees throughout the south-west is a very important conservation issue. Apart from the dwindling supply of hollows in many areas, hollow users must also compete with the introduced feral European honeybee that is infesting hollows throughout our forests.

We are also studying the impact of fire on cockatoos. The January 2005 Perth hills wildfire had a devastating impact on the flora and fauna of the area. This fire affected one of the few known breeding and roosting sites for the Forest Red-tailed Black Cockatoo. Four of the five trees with breeding hollows were destroyed in this fire with the entire tree canopy (including the nest hollow) completely burnt away in three trees, leaving just a stump. Also for several small residual flocks of about 80 birds there was a massive loss of feeding habitat.