I suspect that the violet eye colour in male Satin Bowerbirds is a signal
that it?s sexually mature. While the colour may be as a result of food
pigments in the diet, I think it is more likely to be hormonally-influenced.
The main male sex hormone, testosterone, binds to receptors in cells that
are involved in sexual display, producing the secondary sex characteristics
necessary to attract the attention of females. Testosterone levels are
genetically-influenced (e.g. hereditary levels, age of maturity),
environmentally-influenced [e.g day-length, rainfall, diet (composition and
quantity)], behaviourally-influenced (e.g. presence and behaviour of
females, position in social hierarchy) and the bird?s condition (health,
parasite-loading and age).
Interestingly, male White-winged Choughs have white-pale yellow eyes as
immatures, but become orange-red as they become adults. During the breeding
season, displaying males have bulging red eyes, presumably as a result of
forcing extra blood into blood vessels of the eyeballs. Imagine this
happening in humans!!!!!!
Dr Stephen Ambrose
Research Manager
Birds Australia (Royal Australasian Ornithologists Union)
Australian Bird Research Centre
415 Riversdale Road,
Hawthorn East,
VIC 3123.
Tel: +61 3 9882 2622
Fax: +61 3 9882 2677
Email: S.Ambrose <> (at work)
<> (at home)
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