Here are a couple more references on the subject which provide some food
for thought:
1. Joseph, L. (1989) "Food-holding behaviour in some Australian parrots".
Corella 13(5):143-144.
2. Magrath, D. I. (1994) "Footedness in the Glossy Black-Cockatoo: Some
observations and a review of the literature with a note on the husking of
Allocasuarina cones by this species". Corella 18(1):21-24.
The first paper listed a number of species which appeared to be exclusively
or predominantly left-footed, with the Crimson Rosella being the only
predominantly right-footed example mentioned. The author then put forward
the hypothesis "that exclusive use of the left or right foot for holding
food will be found most commonly in species or populations that feed either
while perched, or by employing specialised feeding techniques, or both". He
suggested testing this by comparing various populations of the Red-tailed
Black-Cockatoo, which varies in its feeding habits and amount of
specialisation.
The second paper noted that most Glossy Black-Cockatoos are left-footed.
Interestingly, two authors were quoted as claiming the species to be mainly
right-footed and these were both probably based on observations of captive
birds, which in one case were bred from a single pair. It was also
suggested that captive birds may have been influenced by food being offered
more from one side of the cage.
The other point that Magrath makes is that the Glossies on Kangaroo Island,
Mt Majura (Canberra) and coastal NSW all husked seed cones from the stem
end outwards, while those near Dubbo NSW husked from the free (distal) end.
This was regardless of food species, with all but the NSW coastal birds
feeding on A. verticillata. Magrath suggested that feeding from the free
end might be a general characteristic of the central-western NSW population
but makes no suggestions as to how this difference might have arisen.
Carol
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