There are several species of grackle with slight variations in body size and proportion, and very slight variations in color, but generally, they are solid, glossy black with irridescent highlights. A couple of years ago, my corner of the office park was frequently visited by an oddity: A common grackle (Quiscalus quiscula) with a neatly defined white ring around its neck.
I had never seen such a bird before, in that office park or anywhere. It suddenly appeared in the spring of 2005, and I saw it several times that summer. I never saw it the next year, and I no longer work in that office park, so I'm not likely ever to see that particular bird again.
The grackle was somewhat camera-shy, so I was never able to get a good picture of it. Here are a few bad pictures:
If you can't see it, just take my word for it. The ring was perfectly symmetrical laterally, narrow across the back of the neck and widening into a little bib across the upper breast.
Curious about how often such an anomaly occurs, I sent these pictures to a birdwatchers' chat board (http://birding.about.com/mpboards.htm) and asked about it. Someone answered that this is a genetic mutation called "leucism". It's not so unusual that it doesn't have a name, but it's unusual enough to be called rare. As my correspondent said, "anyone who notices birds is bound to see it once in a while." It may occur in any black bird, including crows and the true blackbirds, and indeed in any bird or animal.
I have very little idea how long grackles live, or whether they return to the same places year after year, so I'm not sure what to infer from the fact that the bird did not return in 2006. Did it settle somewhere else, and is it perhaps gracing some other office park even now? Did it die untimely because its white marking made it that much more conspicuous to predators?
Whatever became of that bird, I'm sure I'll never see it again. But I am always on the look-out for another white-marked grackle.