Bird Watcher's General Store

Melanistic Mockingbird
03/08/19


Dear Bird Folks,

Please take a look at the photo on my iPhone. It’s an image of a weird bird that has been coming to our backyard. Any idea what it is?

– Steve, Northern NJ

I know that iPhone, Steve,

A year or two ago you brought in the same iPhone and showed me slow motion movies of birds coming to your window feeder. It was fascinating to see how the birds adjusted their wings and flared their tails in an attempt to land on your feeder. Then you showed me how to take slo-mo videos with my own iPhone. I never knew I could do that. I spent the next two weeks recording everything in slow motion. I videoed gulls flying on the beach, Blue Jays grabbing peanuts off my deck and even made a slow motion video of a turtle crossing the street. That last one wasn’t very exciting, but the turtle loved it.

Usually identifying a mystery bird is a quick process. While we might not be the world’s best birders, we can usually handle backyard birds. But this photo had me stumped. I had never seen a bird like it before. I called Casey over to check it out, figuring younger eyes would have a better chance of success. Nope. He was just as baffled. Just then a group of birders walked in. I showed them the photo and none of them had seen a bird like it either. Yet, we eventually figured it out. Here’s how.

The mystery bird was a medium-sized songbird with stark yellow eyes, and with the exception of white wing-patches, it was totally dark gray, almost black. It reminded me of an extremely dark catbird. However, catbirds are friendly and inquisitive. This bird was glaring at the camera with a sinister look, as if it wanted to kill us all. When it comes to identifying odd birds, new bird watchers rely heavily on plumage color. Experienced birders also consider the overall impression they get from the bird. Based on the overall impression (the sinister look), we all decided the mystery bird was a Northern Mockingbird. But why the weird colors?

The plumages of birds are amazingly consistent. As I type this, I’m also watching a steady stream of chickadees coming to my feeder. (If there’s a typo, blame the chickadees for distracting me.) Based on their interactions, they seem to be able to tell each other apart; yet, they all look exactly the same to me. The same thing could also be said about the Song Sparrows and titmice on the feeder. They look like mirror images of each other. But occasionally something goes wrong and a bird is born with an abnormal plumage. The most common of these rare occurrences (common “rare” occurrences?) is when a bird has extra white feathers. It may have a white tail, or white wings or some other strange white parts. For the last few years we’ve had a white-headed House Sparrow eating from the feeders at my shop. Customers line up to take photos of the odd white-headed bird. When people ask me about it, I tell them that it’s a baby Bald Eagle. (Don’t worry, no one believes me…I hope.)

The reason why our sparrow has a white head is due to a shortage of color-producing melanin in its system. Birds with melanin deficiencies are referred to as leucistic (pronounced “lew-sis-tick”). One day a lady from Provincetown brought in a photo of a leucistic grackle. Instead of having an all-white head or tail, this bird’s body was kind of stripy, with alternating white and dark feathers. (I didn’t tell the lady that it was a baby zebra, but I wish I had.) Sometimes, instead of having odd white feathers, a bird’s entire plumage can be diluted or washed out, looking like it’s wearing a faded T-shirt…which is still a good look no matter what my wife says. Leucism should not be confused with albinism. Albino birds are totally white, lacking color of any kind, except for perhaps pink-colored eyes. Wait! If their eyes are pink, how are they considered to have a total lack of color? Good question. Even the irises of albinos may lack color, so the pink we see in their eyes is actually their blood vessels showing through. No offense, albino birds, but that’s a little creepy.

Occasionally, instead of too little melanin, a bird will produce too much. The extra melanin causes a bird to be considerably darker than it normally would. This is what is going on with your mockingbird. Even though mockers customarily have light gray backs and white bellies, the stark yellow eyes, white wing-patches and sinister look of your dark bird provided enough clues for us to figure out its identity. This dark mockingbird is not alone either. I’ve also seen photos of all-black (or nearly all-black) penguins, hummingbirds, herons, flamingos and other freaky-looking birds. (It should be noted that birds with too much melanin prefer to be known as “melanistic.” Calling them freaks is insensitive. I apologize.)

Congrats on your awesome melanistic mocker, Steve. I was going to write a brief explanation of how these birds ended up with such abnormal feather patterns, but it involved a discussion of mutations and recessive genes, and that’s way too complicated for me. After all, I just learned how to use the slo-mo button on my iPhone and that’s all the sciencey stuff I can handle. I’m more of a faded T-shirt kind of guy, and that’s on a good day.




Artwork by Catherine Clark


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