Why Is A Mallard Drake's Head Green? Or Sometimes Blue/Purple?

If mallards weren't so common, we'd all go nuts when we see them.  The iridescent green head is so striking, and the white right around the neck!  But familiarity breeds, maybe not contempt, but loss of sensitivity to their beauty.

But sometimes, in different light, the head looks blue or dark purple.  (I really would have cropped this to just show the water patterns, but since I need to show you a blue/purple head, I left that in too.)

I thought I'd find out how this works - the color change.  I didn't quite, but I found an interesting blog post at the Nature Niche that not only talks about the color change, but also about mallard drakes whose heads stay blue.

While watching the ducks on a pond at Crystal Lake Fish Hatchery (Shasta County CA) one mallard caught my attention. The head of this mallard was blue. Because the iridescence and color of birds is affected by the angle of observation, I watched this particular mallard for nearly fifteen minutes, yet the blue color never varied. This was not a blue-green color nor was the mallard’s head simply “dark”  due to shadows – the head was a constant, beautiful, rich blue. On occasion I hear about a blue-headed mallard and have even seen mallards whose heads seem blue in certain light. But the blue head color proves in reality to be brilliant green when the duck moves. No matter how this duck moved or how the light changed, its head was blue. I wondered why?

He doesn't claim scientific proof, but did collect some research online.

According to Nina G. Joblonski  in her book “Living Color”, the intensity of the mallard’s  iridescent green head feathers is related to the level of testosterone, higher levels of this hormone resulting in brighter green color. But since a non-breeding or eclipse male has a nondescript brown head similar to the female, where does a blue head enter the picture?

But, Steve, you still haven't explained why sometimes green and sometimes blue/purple in the same bird.  I didn't find the answer exactly, but here's something on butterflies:

The combination of a butterfly's structural and pigmented color can create interesting effects. For example, if you saw a butterfly with yellow pigment underneath a structure that creates a blue iridescent color, you might see a green shade, made by the merging of the two colors. Or depending on your viewpoint, you might see blue, yellow, green or a combination of the three. Your view would change as the butterfly moves its wings and the light enters at different angles.

These shots come from my walk around the park yesterday after dropping off my granddaughter at her pre-school.  Unlike the other day when the good pictures were hiding in the grey, yesterday they were right out there daring this photographer to try to catch them.  I'll offer a few where I got close.

First I caught the flattened reeds floating in the water.   But then I saw the sun was floating just below.  You can see where the two pictures would overlap if I combined them, but I'll leave them separate.  It forces you to look at both pictures a little more carefully.

A little later, the sun dared me to shoot it straight on, not as a reflection.

This robin was holding its ground.

There are also signs of humans in the park.  (Beyond the folks walking their dogs or jogging and the benches etc.)

And this rhododendron bush that was blooming despite the delayed spring weather.

This was all on Bainbridge Island, a short ferry ride from downtown Seattle.