G'day Richard,
I think you have misunderstood what Stephen was saying, three factors to
consider.
1- a given population of Brown Falcons say at Werribee or where ever, does
not consist of a number of different morphs. The differences in plumage are
primarily the result of differences between the sexes overlaid by increasing
paleness as the individuals get older.
2- there are regional differences eg. birds in Central Aust are paler more
"Kestrel like", birds from the Kimberley are very dark. There are other
features of difference between these regional types beyond pale and dark
which I am not going to go into here, but the important thing to understand
is that a pale regional type from Central Aust and a very old pale male from
Werribee are not the same thing, they don't look identical. Same for the
dark Kimberley/Top end birds, there is no equivalent found elsewhere. These
are regional types.
3- yellow cere is apparently only found in the older males especially the
pale Central Australian population, Stephen suggested this may possibly be
because they are for unknown reason more likely to reach the prerequisite
older age.
Cheers Jeff.
-----Original Message-----
From:
On Behalf Of Richard
Nowotny
Sent: Wednesday, 5 October 2011 8:02 PM
To: 'Birding Aus'
Subject: Brown Falcons with yellow cere and bare facial parts
Thanks Shirley for seeking informed comment from Stephen Debus - very
helpful (as one would expect). It does however raise the question (alluded
to by Stephen in his response) of whether there really are "pale-plumaged"
individuals, implying that there are also darker-plumaged individuals of
similar age (rather than them being just fully mature individuals which are
intrinsically pale by virtue of their age). Can anyone comment on this?
Does anyone know how I/we might access the article by Paul McDonald referred
to by Stephen? (I have been aware of this research and its findings for some
years but have not ever read the article.)
Thanks. Richard
From: Stephen Debus
To: Shirley Cook
Cc: Christopher Watson
Sent: Wednesday, October 05, 2011 2:19 PM
Subject: Re: Fw: [Birding-Aus] Brown Falcons with yellow cere and bare
facial parts
Hi Shirley & Chris,
Yellow cere is a character of fully adult males, and seems to be
particularly prevalent in pale-plumaged individuals (e.g. remote areas like
the Centre), perhaps where the falcons live long enough to develop the 'old
male' characters of yellow cere and eye-ring, and white breast. See:
McDonald PG (2003) Variable plumage and bare part colouration in the Brown
Falcon, Falco berigora: The influence of age and sex. Emu 103, 21-28.
Cheers,
Steve
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