Eye color in birds is rich and varied, spanning a range from white to yellow to orange, deep red, brown and black iris color. The color of the iris might change seasonally, as it does in Brown Pelicans and Double-crested Cormorants (see below);
or might vary with age, as it does in various raptor species from pale yellow in juveniles to dark brown in adults;
or it might be associated with other flamboyant colors of males advertising their sexual prowess, like the bright red eyes of the Wood Duck,
or the deep golden-orange eyes of the Glossy Starling seen in South Africa a month ago.
With such a diversity of eye color, within a species or over the bird’s lifetime, it seems strange that birds seem to lack the green and blue-hued eyes that are common in other animals, and especially in humans. A couple of the very few examples of green/blue eyes in birds:
Green-eyed birds are either really rare, or rarely photographed; I found only one image of a bird with this rare iris color — a Great Cormorant. (Note: there are other images of green-eyed birds posted on Google, but some definitely look photo-shopped — see below.)
I didn’t realize until I was looking for more information about “green eyes” that they are rather rare in the human population as well. Only 1-2% of humans have truly green eyes (not hazel with flecks of green). That makes my paternal grandmother, me, my daughter, and my grandson rare! Hmm…that doesn’t sound too rare.
Green color, being a combination of yellow and blue, requires a yellow pigment and a refractive property that reflects blue light (because there are rarely blue pigments that produce color). In humans, amber and green eye color is produced by a yellow pigment called lipochrome. Varying amounts of lipochrome and melanin present in the iris generate a host of eye colors varying from yellow-brown to deep, intense grade shades. Click here to read a fascinating discussion of the derivation of eye color on a blog devoted entirely to that subject.