Not Quite Black and White

We went to Indiana this past weekend for an extended-family reunion of Annie’s, during which time I saw an unidentified flicker, redwing blackbirds, a kingfisher, various mallards, a distant turtle, what was probably a chipping sparrow, a multitude of swallows, and a ton of mute swans. And Annie’s relatives too, of course, but they, being human, won’t feature in this blog.

The swans were all over the lake next to which we stayed, drifting along in flocks of up to 20 birds. (I hadn’t realized swans were so social, but Annie’s mother pointed out that maybe they, like we, were on vacation and so more inclined to be gregarious.)

We also spotted a swan family: three half-grown cygnets and their parents, sculling calmly along the edge of the lake. They kept a wary eye on us—and even hissed warningly at Annie when she tried to get too close—but by and large they didn’t seem too concerned about anything except pulling up and eating water weeds.

As you’ll notice in the photos, one of the cygnets was white, while the other two were grey. They were all, as far as I could tell, the same age, so it wasn’t as if one was in a different stage of development than the others. What was going on?

I conducted a Google search on “color variation in cygnets” and found, to begin with, this article from the 70s on “The Color Phases of Downy Mute Swans”. It claims that color in mute-swan cygnets is a “sex-linked recessive” trait, with white being the recessive allele and grey the dominant. The NY State Department of Environment website says that mute-swan cygnets can be white or grey and that the “color at hatch is a genetic trait and not related to sex”—which makes sense up to a point (i.e., you can’t tell a male or female by its color) but is kind of inaccurate if the gene is sex-linked. But I digress.

Another article from the 70s (Norman 1977), of which I could only access the abstract, claims that adult mute swans treat cygnets differently based on color and are much more aggressive towards white youngsters than grey ones (I guess because the white ones look like adults).

I made a slight attempt to pursue this topic (searching for articles that had cited this one), but I didn’t find anything relevant, so I don’t know if this paper was simply the authoritative Last Word on the subject or if nobody read or believed it.

I saw no evidence of discriminatory behavior on the part of the mute swan parents in this family; I’m not sure if that refutes anything or if this was just an especially progressive couple.

Or maybe one of the parents was white as a cygnet, too, and remembers the tough breaks s/he got and didn’t want to repeat the experience.

Or maybe s/he was raised lovingly and wanted to pass that on.

Or maybe I spent too much time at a family reunion. I’ll let you be the judge.

{A note: I do write all text and take all pictures. Please do not reproduce either without my permission.}