Stephen:
Thanks for the reply. If I may continue this discourse...
On Thu, 26 Mar 1998, Stephen Ambrose wrote:
> 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.
Can you elaborate on what you mean by "preferred colour in some...robins"?
I have been fascinated by the idea that there is a match between eye
colour of bowerbirds across several species and the items choosen to be
displayed near the bower. With regard to the Satin Bowerbird, I would
like to believe that the blue eye colour isn't a random choice, but
predicated on the female's preference for blue independent of the male's
behaviour. For example, she might perfer blue because many fruits are
blue...being attracted to blue hence draws her to investigate the blue
items in a male's bower, selects for blue eye colour and bluish tinged
plumage...and the process is set into motion.
In this scenario, the male is also likely to prefer blue. There is also
the possibility that the blue iris colour is actually used to enhance the
bird's vision (maybe acting like a blue filter). UV light may also be
involve here as well. Of course, these are just ideas, but they could
genrate some very testable predictions.
>
> 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.
You lost me here. Since humans can't preceive UV, how could we view UV
under a UV 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.
>
This would be fascinating. There are a few studies that suggest that this
is the case (e.g. on Bluethroats in europe).
> >... 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.
>
Seem reasonable and I wonder if by so doing, the male runs the risk of
showing off imperfections in the contour, colour, etc. of the eyes? The
context in which the male performs eye-gorging could perhaps provide some
clues.
Steve's comment concerning the opening/closing of iris by Amazon
parrots might be relevant here...both would seem to be some sort of
display.
> There are some good photos of iris colour of choughs from different age
> groups in Rowley 1974 ("Bird Life": Collins, Sydney)(opposite p. 97).
>
I have seen them, thanks. Very interesting stuff.
Cheers, Jim
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