Pochard-(Goldeneye Head Colour Issue)-Iridescence

[Kevin Vang <>]

Dear Group

Growing up in Northern Scandinavia, we always had this problem of the head colour of Goldeneyes.  The Barrow’s Goldeneye commonly has a “purple head” and the Common Goldeneye commonly has a “green head”.  However, depending on how the angle of sunlight hit the head, the iridescence off feathers would yield the exact opposite colour.  This always results in the over-reporting of Common Goldeneyes in Lappland and of Barrow’s Goldenhead’s in more southern climes.

Visit the following website to see the same Common Goldeneye with what is obviously two completely different head colours.

www.schmokerorg/BirdPics/BAGO_COGO.html

I was wondering whether this may be a factor with the Baer’s Pochard in part anyway?  Now I guess the only question is, “Do Hardheads’ Heads iridesce?”  (Say that 5 times quickly) ;-)

See also

http://www.whozoo.org/ZooPax/ZPFeather.htm

Some of the brightest feathers are a sort  of optical trick. The surface of the feather has microscopic ridges, like the surface of a CD. Light striking the ridges is broken up like light passing  through a prism, and the color of the bird depends on the wave-length of the  light leaving the feather. Because this is similar to what happens when light  is diffracted through water droplets to make a rainbow, this kind of color is  called iridescence (Iris is the Greek goddess of the rainbow). Blue and green  feathers are nearly always produced by iridescence, as well as some brilliant  reds and yellows. The color of the blue feather above is this kind of color  Curiously enough these feathers must have melanin in order to project their  blue structural color.

Kevin