This successful fledging of both nestlings raises a number of questions, such as the following: in what proportion of nesting attempts does this occur is the raising of two nestlings achieved at a cost to one or both nestlings is there a net benefit to the species in being able to fledge both nestlings and does the species' current environment support such a strategy? A review of field data collected on Carnaby's Cockatoo since the study reported by Saunders (1982) at Coomallo Creek and in other areas has also shown that a number of hollows in which two eggs are laid result in two nestlings that survive for longer than 1–2 days in some cases, both nestlings have fledged. During the same period at Manmanning there were no instances of two nestlings from the same nest hollow surviving to fledge. That study showed that between 19 at Coomallo Creek, eight of 222 (3.6%) nesting attempts fledged both nestlings. Saunders also reported that in two-egg clutches, when both eggs hatched, the younger nestling most commonly died within 48 h of hatching. Average clutch size was larger at Coomallo Creek than at Manmanning.
Location of each study area that produced two nestlings aged 14 days or more and the extent of native vegetation remaining within a 6 and 12 km radius of the nest hollows in the ‘Midlands’ ( a) and ‘Great Southern’ ( b).īased on studies at Coomallo Creek and Manmanning, Saunders (1982) reported that Carnaby's Cockatoo lays one or two eggs, with two being more common. In addition, the species has been studied in less detail at Nereeno Hill and in the wider ‘Midlands’ region of the northern wheatbelt and at Tarwonga, Moornaming and the wider ‘Great Southern’ region in the southern wheatbelt (Fig. Those studies were based on two populations at Coomallo Creek and Manmanning, both in the northern wheatbelt. The ecology and behaviour of this species have been studied in detail since 1969 ( Saunders, 1982 Saunders and Ingram, 1998). It is listed as endangered under the Australian Environment Protection and Biodiversity Conservation Act 1999 and as ‘Fauna that is rare or likely to become extinct’ in Schedule 1 of the Western Australian Wildlife Conservation (Specially Protected Fauna) Notice 2012(2) under the Wildlife Conservation Act 1950. In Yellow-tailed Black Cockatoo and Carnaby's Cockatoo, when both eggs hatch, the younger nestling usually comes from a smaller egg and dies within 1–2 days of hatching ( Saunders, 1982 Higgins, 1999 Forshaw, 2002).Ĭarnaby's Cockatoo is endemic to south-western Australia. Little published information is available on the breeding of Baudin's Cockatoo (560–770 g). Red-tailed Black Cockatoo ( Saunders, 1977 body weight 530–870 g) and Glossy Black Cockatoo ( Garnett et al., 1999 400–460 g) lay single-egg clutches, while clutch size is variable in Yellow-tailed Black Cockatoo ( Saunders, 1979a 505–900 g) and Carnaby's Cockatoo ( Saunders, 1982 480–790 g weights and clutch sizes from Saunders, 2009), but clutches of two predominate. The five recognized species of black cockatoo in the genus Calyptorhynchus do not conform to this pattern. The Australian cockatoos (subfamily Cacatuinae) are the largest species of Australian parrots, and most members conform to this pattern. In the Psittaciformes, despite the variation in the number of eggs in the clutches of some species, there is an inverse relationship between average clutch size and body weight ( Saunders et al., 1984). The conservation implications of these findings are discussed in the light of predicted changes to the climate of south-western Australia. Sets of siblings are usually the product of older, more experienced females nesting in areas where more native vegetation has been retained. However, the species is capable of fledging both nestlings from a breeding attempt.
While both eggs hatch in 77% of two-egg clutches, the species normally fledges only one young. While the usual clutch size is two, average clutch size tended to be lower in areas where much native vegetation has been cleared. There was a significant negative relationship between the health of nestlings and percentage loss of native vegetation around nest hollows. When raising nestlings the species feeds on seeds of native vegetation, and there was a strong but not significant negative relationship between nesting success and percentage loss of native vegetation within 6 and 12 km of nest hollows. The breeding of the endangered Carnaby's Cockatoo has been studied from 1969 to 2012 at a number of localities throughout its range in south-western Australia within a region largely cleared for agriculture. Of the five species of black cockatoo in the genus Calyptorhynchus, those species with red tail bands (Red-tailed Black Cockatoo and Glossy Black Cockatoo) lay clutches of only one egg and those with white or yellow tail bands (Carnaby's Cockatoo, Baudin's Cockatoo and Yellow-tailed Black Cockatoo) usually lay clutches of two.
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