All very interesting my curiosity is around the word "probably" in:
"Cross-fostered C. roseicapilla are probably responsible for those cases of
hybridisation in the wild between and C. leadbeateri that have been
reported."
It sounds like a very plausible working hypothesis and likely to be true.
But is it.
Philip
-----Original Message-----
From: Birding-Aus On Behalf Of
Graeme Chapman
Sent: Thursday, 3 September 2015 10:24 AM
To:
Subject: X Breeding in the wild.
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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