Dear Chris and Simon,
I actually think that this variation is more likely to be associated with age
and sex differences than plumage 'phases'. Male Brown falcons at Werribee
tended to be lighter (front) and redder (back, legs) than females. Further,
males have more yellow and less blue in their cere and orbital rings than
females, and this seems to get brighter as they get older in both sexes. There
are some photos in the below article, although they aren't close enough to see
bare parts in detail. For those interested, I can send photos of typical young
and adult heads of each sex off-list.
Thus, while it is too early to prove it conclusively, I'm pretty confident that
the 'phases' of brown falcons aren't likely to stand up, but rather are more
likely to be representative of age and sex differences, with birds becoming
lighter and possessing more yellow in their bare parts as they age,
particularly males. The lighter part at least is consistent across several
raptor species (e.g. think black falcons with white bibs). Differences
according to region on the record are most likely due to incomplete sampling,
or sampling that is influenced by recent events at given locations, e.g.
marginal/ephemeral areas are more likely to have lots of younger and thus
darker birds, established areas older, lighter birds that hang onto territories
for consecutive years and so on. Nonetheless it would make an interesting study
to look at these differences across their range in more detail.
The bird in question looks like it has all the features typical of an adult
male that is at least several years old. Their plumage can be variable,
granted, but the patterns described below (sadly post-Hanzab) have held up and
made sense for the falcons that I have been looking at ever since.
For those interested, the published details of that study can be found here:
McDonald P.G. 2003 Variable plumage and bare part colouration in the Brown
Falcon Falco berigora: the influence of age and sex. Emu 103(1), 21-28.
Happy birding ,
On 04/10/2011, at 1:13 PM, Simon Mustoe wrote:
> Great photos!
> HANZAB plates very clearly depict the rufous phase of Brown Falcon as having
> yellow cere and orbital ring. Though the text misleadingly, only refers to
> grey or white. So I assume there is a common precedent amongst the rufous
> forms to have this yellow bare part colouring.
> Simon Mustoe
> Tel: +61 (0) 405220830 | Skype simonmustoe | Email
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>> Date: Tue, 4 Oct 2011 00:47:17 +0930
>> Subject: [Birding-Aus] Brown Falcons with yellow cere and bare facial parts
>> G’day birders,
>> I’ve got a question which has been nagging at me for a while. I hope someone
>> will know something.
>> Brown Falcons keep turning up with yellow ceres and bare facial parts. I
>> have a growing collection of photographs of these birds from Lake Eyre
>> through Central Australia and out to the western extremities of the Tanami
>> Where does this colouring come from? Is this a regional variation? Is anyone
>> aware of any research/study that has been done on this subject?
>> Some photos of my latest encounter with this colour variation are on my blog
>> I’m intrigued.
>> Chris Watson
>> Alice Springs
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Dr Paul G. McDonald
Zoology, School of Environmental and Rural Sciences
University of New England
Armidale NSW 2351
Ph: +612 6773 3317 Fax: +612 6773 3814
Publication list: http://publicationslist.org/paul.mcdonald
Thompson ISI Researcher ID: http://www.researcherid.com/rid/A-5928-2010
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