Journal of the Royal Society of Western Australia, 86:139-142, 2003 
Characteristics of Marri (Corymbia calophylla) fruits in relation to the 
foraging behaviour of the Forest Red-tailed Black Cockatoo 
(Calyptorhynchus banksii naso) 
CE Cooper 12 , PC Withers 1 , PR Mawson 3 , R Johnstone 4 , T Kirkby 4 , J Prince 1 , 
SD Bradshaw 1 & H Robertson 5 
1 Zoology, School of Animal Biology M092, University of Western Australia, Crawley WA 6009 
2 Present address: Centre for Behavioural and Physiological Ecology, Zoology, 
University of New England, Armidale NSW 2351 
3 Wildlife Branch, Department of Conservation and Land Management, 
Locked Bag 104, Bentley Delivery Centre WA 6983 
4 Western Australian Museum, Francis Street Perth WA 6000 
5 Perth Zoo, South Perth WA 6151 
El ccooper9@pobox.une.edu.au, pwithers@cyllene.uwa.edu.au 
Abstract 
Forest Red-tailed Black Cockatoos ( Calyptorhynchus banksii naso) feed predominantly on seeds of 
the eucalypt Marri ( Corymbia calophylla) and often only from specific feed trees. There was no 
difference between wet weight of fruits from feed (24.1 ± 1.72 g) and non-feed trees (23.2 ± 1.57 g), 
but trees from which Forest Red-tailed Black Cockatoos fed had a significantly higher seed number 
per fruit (3.9 ± 0.18), a greater individual dry seed weight (0.10 ± 0.003 g) and total seed weight per 
fruit (0.39 ± 0.02 g), and a higher ratio of total seed dry weight to fruit wet weight (0.02 ± 0.001) 
compared with non-feed trees (3.1 ± 0.20 seeds per fruit; 0.09 ± 0.005 g individual seed dry weight; 
0.29 ± 0.020 g total seed dry weight per fruit; 0.013 ± 0.001 ratio of total seed dry weight to fruit wet 
weight). Discriminate analysis had a limited capacity to predict Marri use by Forest Red-tailed 
Black Cockatoos, correctly classifying about 70 % of feed trees. Seed number and total seed mass 
were the best fruit characteristics for the prediction of tree type. We conclude that Forest Red-tailed 
Black Cockatoos selectively forage from trees with fruits that have a high seed yield, but the 
method by which the cockatoos select these trees is unclear. 
Key words: cockatoo, marri, food selection, seeds, parrots, eucalyptus 
Introduction 
The Forest Red-tailed Black Cockatoo ( Calyptorhynchus 
banksii naso) inhabits tall eucalypt forests of Marri 
(Corymbia calophylla), Jarrah ( Eucalyptus marginata) and 
Karri (E. diversicolor) in the south-west of Western 
Australia (Saunders el al. 1985; Saunders & Ingram 1995; 
Johnstone & Kirkby 1999). The geographical distribution 
and abundance of this sub-species of Red-tailed Black 
Cockatoo is suspected to have declined over the past 50 
years (Saunders & Ingram 1995); it is considered to be 
rare to uncommon throughout its range (Johnstone & 
Storr 1998; Johnstone & Kirkby 1999), and is listed as 
near threatened (Garnett & Crowley 2000). 
The Forest Red-tailed Black Cockatoo feeds on seeds 
of a variety of species of native flora, including Jarrah, 
Karri, Blackbutt (£. patens), Albany Blackbutt (E. staeri), 
Common Sheoak (Allocasuarina fraseriana) and 
Snottygobble (Persoonia longifolia), but Marri seeds are its 
principal food source Qohnstone & Kirkby 1999). Flocks 
appear to select specific Marri trees when feeding, 
returning to the same tree until its food supply is 
exhausted and often ignoring neighbouring trees. 
Johnstone & Kirkby (1999) suggested that the quality of 
the fruit varies between trees selected and ignored by 
these cockatoos, and that the quality of food might limit 
the breeding success and long-term distribution and 
© Royal Society of Western Australia 2003 
abundance of Forest Red-tailed Black Cockatoos. Cooper 
(1999) reported that the fruits of feed trees had a higher 
seed yield than non-feed trees. We examine here fruit 
characteristics (fruit mass, seeds per fruit and seed mass) 
to further determine differences between fruits of feed 
and non-feed Marri trees of the Forest Red-tailed Black 
Cockatoo. 
Methods 
Fruits from feed and non-feed Marri trees of the Forest 
Red-tailed Black Cockatoo were examined at Armadale, 
Jarrahdale and north of the North Dandalup Dam, south¬ 
east of Perth, Western Australia (31° 58' S, 115° 51' E), in 
1999 and 2003. Feed trees were identified either by 
observing birds feeding from a particular tree, or by 
observing freshly chewed fruits scattered at the base of 
the tree. Non-feed trees had no fruits opened and 
discarded by Forest Red-tailed Black Cockatoos beneath 
them. Three other species of parrot also feed on these 
Marri fruits, Baudin's Cockatoo (C. baudinii), Carnaby's 
Cockatoo (C. latirostris) and the Red-capped Parrot 
(Purpureicephalus spurius). Each species leaves 
characteristic marks on discarded fruits (Cooper 1999, 
2000), and so trees from which the Forest Red-tailed 
Black Cockatoo had been feeding could be easily 
identified. 
Six fruits were collected from each feed tree and from 
the nearest non-feed tree using long-handled clippers. 
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