That's good, thanks for this, I wonder what to make of the very pale grey
birds that can be be mistaken for Grey Falcons?
John L
On 4/24/06, Andrew Taylor <> wrote:
>
> On Mon, Apr 24, 2006 at 04:02:34PM +1000, John Leonard wrote:
> > Alan Morris alluded to an article in the Emu which has proved that the
> > phases of the Brown Falcon are age-related colour changes.
> > Could someone summarise this article in a few sentences for us? Alan?
>
> Courtesy http://www.publish.csiro.au/nid/96/paper/MU02028.htm
>
> Variable plumage and bare part colouration in the Brown Falcon, Falco
> berigora: the influence of age and sex
>
> Paul G. McDonald
>
> Abstract
>
> The Brown Falcon, Falco berigora, is one of Australasia's most common
> raptors, yet considerable confusion remains over the influence of
> geography, age and sex on plumage and bare part colouration in this
> species. To address this issue, 160 immature and adult falcons from
> an individually marked, closely monitored population were examined. In
> contrast to previous studies, all were of known sex, age-group and part of
> the resident population or their offspring. Adult males had significantly
> lighter upperpart, cap, ventral and underwing covert plumage in comparison
> with other birds, closely resembling what has previously been described as
> a 'rufous morph'. Immature females were significantly darker than other
> ages and sexes in upperpart and underwing covert plumage, resembling
> descriptions of 'dark morphs'. In contrast, plumage of immature males
> and adult females tended to be similar and intermediate between these
> extremes, resembling the 'brown morph'. The buff-tinged, not white,
> ventral plumage and darker underwing covert plumage of immature males
> separated them from adult females. Cere and orbital ring colour also
> differed with sex and age: immature females had the dullest facial bare
> parts and adult males the brightest, adult females and immature males
> again being intermediate between the two. The results indicate that most
> variation in plumage and facial bare part colouration observed in the
> population could be attributed to age and sex differences as opposed to
> racial clines or the existence of colour morphs. Moreover, the brighter
> colours of adult falcons may function as honest signals of quality.
>
> Emu AUSTRAL ORNITHOLOGY 103(1) 21 - 28 2003
>
> Andrew
>
>
--
John Leonard
Canberra
Australia
www.jleonard.net
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