On Wed, Nov 13, 2002 at 05:31:57PM +1100, wrote:
> I saw what i think was a Pacific Black Duck today, however it had a
> patch of purple feathers where the green colouration usually is???
> Can anyone please enlighten me as to what this denotes(male, female ,
> different species)???
The green in the Pacific Black Duck's speculum is a structural
colour. This means the colours is not caused by pigments (alone)
but by microscopic structure in the feathers at a size similar to the
wavelength of visible light. A consequence is that the colour of the
PBD feather varies with the angle of viewing from green to purple.
Anti-reflective coatings in binocular lens work in a similar manner.
Alternatively, you may have been looking at female Mallard or
Mallard-hybrid which have a bluer speculum than a PBD.
Andrew Taylor
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