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
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