>... Satin Bowerbird eyes
>What is the colour of male and female juveniles?
>
My recollection is that they are a dark blue that eventually lighten to
violet colour described earlier today by Syd, but someone may correct me on
this.
> ... testosterone and eye colour ...
>Nicely put, however this arguement is a proximate explanation. Could there
>be another reason why purple/blue was evolutionarily choosen?
Sure, I agree that I've just described a possible mechanism rather than
reason for the colour. I don't have an answer to your question. I would
like to know why BLUE is the dominant colour in the plumage of
sexually-mature male fairy-wrens, and RED seems to be the preferred colour
in some Petroica robin species, etc.
Some plumage patterns and colours reflect ultra-violet light which can only
be detected by the human eye when viewed under an ultra-violet light
source. If birds are more sensitive than humans at detecting reflected
wavelengths at the UV end of the light spectrum, then maybe evolution
favours colours and patterns that reflect UV light.
>... White-winged Choughs
>Is the red colour of an unexcited male due to blood or a pigmented iris?
>
I'm not sure, but I suspect it is due to pigment. I think the gorging of
the eyeball with blood in an excited male just serves to make the eye
larger and more obvious.
There are some good photos of iris colour of choughs from different age
groups in Rowley 1974 ("Bird Life": Collins, Sydney)(opposite p. 97).
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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