Cross-Fostering, Imprinting and Learning in Two Sympatric Species of Cockatoo

Abstract

Two species of cockatoo, the galah Cacatua roseicapilla and Major Mitchell's cockatoo C. leadbeateri are sympatric throughout much of Australia. Both species nest in tree-hollows of similar dimensions at the same time of year. Their eggs which are very similar are laid every other day and are not incubated until at least three have been produced. Parent birds often forage a long way from the nest and so the early eggs are largely unattended. Sometimes a pair of C. roseicapilla and one of C. leadbeateri both "own" the same hollow and contribute eggs to the clutch. When confrontation finally arises the C. roseicapilla being smaller, lose out and the C. leadbeateri unknowingly incubate a mixed parentage clutch, and may rear a young C. roseicapilla with their own offspring. Such cross-fostered C. roseicapilla behave as, and associate with C. leadbeateri; they ignore other C. roseicapilla. Parts of their behaviour repertoire are innate, parts are the result of imprinting and parts, of later learning. They learn to fly and to call like C. leadbeateri and they also adopt the latter's much more varied diet. Cross-fostered C. roseicapilla are probably responsible for those cases of hybridisation in the wild between C. roseicapilla and C. leadbeateri that have been reported. Two species of cockatoo, the galah Cacatua roseicapilla and Major Mitchell's cockatoo C. leadbeateri are sympatric throughout much of Australia. Both species nest in tree-hollows of similar dimensions at the same time of year. Their eggs which are very similar are laid every other day and are not incubated until at least three have been produced. Parent birds often forage a long way from the nest and so the early eggs are largely unattended. Sometimes a pair of C. roseicapilla and one of C. leadbeateri both "own" the same hollow and contribute eggs to the clutch. When confrontation finally arises the C. roseicapilla being smaller, lose out and the C. leadbeateri unknowingly incubate a mixed parentage clutch, and may rear a young C. roseicapilla with their own offspring. Such cross-fostered C. roseicapilla behave as, and associate with C. leadbeateri; they ignore other C. roseicapilla. Parts of their behaviour repertoire are innate, parts are the result of imprinting and parts, of later learning. They learn to fly and to call like C. leadbeateri and they also adopt the latter's much more varied diet. Cross-fostered C. roseicapilla are probably responsible for those cases of hybridisation in the wild between C. roseicapilla and C. leadbeateri that have been reported.