Blue-headed Mallard

As one of the most common ducks in North America, most everyone is familiar with the iridescent green head of the male mallard (Anas platyrhynchos). Feather color, as I mentioned in an earlier post, is determined by pigments, the structure of the feather or a combination of both.

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?

I certainly have not done a comprehensive review of the literature, but I could find no explanation for this blue-headed mallard although as I thought about the little information I had, I came up with several theories, one of which I will mention. Please remember, what follows are simply my musings, not, to my knowledge,  scientific fact.

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?

Eberhard Haase et. al. (reported in “Pigment Cell Research”) studied the pheomelanin and eumelanin levels in mallard duck feathers. Melanin is a pigment in feathers. Pheomelanin is a more yellow form and eumelanin is more brown. Without going into the entire content of their research, let me note, in a very superficial manner, that Haase and his colleagues found that males, as their testosterone levels rose in the spring, developed significantly more of the yellowish pheomelanin in their feathers while the brown eumelanin declined. Females displayed more of the brown eumelanin in their feathers. Following so far?

Remember from high school physics that green is a combination of the primary colors blue and yellow. Is the blue color (structural or pigmented?) of mallard head feathers disguised by the brown eumelanin in females and in males whose testosterone is low outside of the breeding season? Then as the male’s testosterone level begins to increase in the spring, the blue shows through as the eumelanin decreases. After the amount of yellowish pheomelanin gets high enough, the head feathers appear green since blue and yellow make green.

A mallard with a blue head could, repeat could, simply not have a high enough testosterone level to produce enough yellow pheomelanin in the head feathers to make the feathers appear green. This lack of testosterone could result from a genetic inadequacy or perhaps the mallard was a young male that still was not making enough of the hormone. Or. . . ?

I certainly do not know the correct answer. Yet speculating is an interesting mental exercise.

I would love to know why this mallard’s head appeared to be truly blue and not simply an optical trick.

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14 Responses to Blue-headed Mallard

  1. Christine Corcoran says:

    I also have just seen a blue headed male mallard along with a flock of a dozen or so other mallards, mottled ducks and mallard mottled hybrids. The blue headed one comes to eat cracked corn on his own, apart from the group and is a bit timid, otherwise I haven’t noticed any other unusual behavior, he is new to this group.

  2. Sarah SSM says:

    I have just seen a bunch of purple-headed mallards in Jamaica Pond in Boston. Can’t figure out what’s going on! More than one. I have (not very good) pictures I took with my phone.

  3. Jen says:

    I just saw one this morning hanging out in my pool!

    The fact that it was blue is what caught my eye and made me watch. We’ve had a green headed one hanging out there for a few days. Blue was a new one.

    I’m in Joliet, IL :)

  4. Nora says:

    I heard a duck fight next to our neighbour’s dock on Orr Lake this morning, which caught my attention. Two drakes appeared to be fighting over a female. After the battle was won, the pair came to our dock to dry off. She definitely is a mallard. He definitely has a blue head, and appears in other ways to be a mallard. I checked our bird book, which says that mallards have a blue violet spectrum, which this one did, and the head was the same colour. This drake certainly seemed to have plenty of testerone, based on the way he was attacking the other drake!
    This is in southern Ontario, Canada, just north of Barrie.

  5. Ruth Halligan says:

    I have a blue-headed mallard in my pond right now. I’ve been trying to find out what the heck kind of duck this thing is. Just found your site with pictures. That’s my duck! I’m located in Bethel, NY. I am so happy to have an answer. (Sibley was no help.)

    • Jenny says:

      I too am looking at this beautiful duck, I thought that it was black but with binoculars in the beautiful sun it appears to be deep purple or as you say blue. He was cleaning his wings on top of a rock on my lake that also had that beautiful purple/blue color on it. This is the second time in 2 years since I have had the privilege to witness such unusual beauty.

  6. Bill says:

    I came across your post looking for answers as well. I keep seeing these in the lake behind my house in Orlando Fl. I had the same thought as you, maybe just a weird angle. Today though, I got a lot of close up pictures of a group of green head and blue head mallards and they definitely have bluish purple heads. another thing i noticed was the bills on the blue heads were a slightly lighter yellow than on the green heads. Upon further observation, the blue heads actually seemed to be more aggressive and dominating than the green as well. Maybe slightly larger too, unless that was just illusion. But they definitely seemed to be the leaders of the group. Maybe another weird hybrid?

    • gingkochris says:

      I did not notice the bill color nor did I note more aggressiveness in the blue-heads. If I ever come across blue-headed mallards again I will be certain to look more closely at their bills and observe their behavior. Nice to know you did see blue-heads. More confirmation I was not imagining.

  7. Pingback: Mallard and Her Ducklings | The Nature Niche

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