Cross breeding in closely related parrots in the wild is well known, but the
reasons why and the associated life history mechanisms are not.
Many years ago when, with Ian Rowley, I was lucky enough to study Major
Mitchell's Cockatoos for some years in Western Australia, we were able to
document, using marked individuals, just what happens.
This was published in the journal "Behaviour", the paper entitled
"CROSS-FOSTERING, IMPRINTING AND LEARNING IN TWO SYMPATRIC SPECIES OF COCKATOO"
in Vol 96, Issue 1, pp 1-16.
For those unable or less inclined to access this reference, the abstract
reads:-
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 inate, parts are the result of imprinting and parts,
of later learning. They learn to fly and 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 and
C. leadbeateri that have been reported.
So essentially, the initial reason for all this is a shortage of nest hollows.
Parrots, on the whole have traditional nest sites, that is they use the same
one year after year, so if an interloper comes along and pops an egg in early
in the peace, that's where the story really starts.
My memories of watching one of our main young imprinted galahs, tagged NO, are
still vivid after 40 years; seeing her leading the flock of 50 or so Majors,
flying like a Major, calling like a Major - always at the head of the flock
because the galah had difficulty flying slowly enough.
It was rather sad to watch her when she eventually became adult and tried
cuddling up to a handsome young male Major Mitchell, only to be continually
rejected by him, and effectively in limbo.
For a long while I've been meaning to write an illustrated version of this
story for a more popular magazine. I have a stunning picture (made by me) of a
Galah looking at its reflection in a puddle where the reflection is actually a
Major Mitchell which I entitle " Mirror, mirror on the wall ........"
Graeme Chapman
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