My friends often describe squirrels, to my great indignation, as “rats with prettier tails.” I will spare you my feelings on this—suffice it to say that, obviously, the trash-scavenging conditions of squirrels in urban areas has more to do with human encroachment on their habitat than any fault of their own (also, I really love rats)—but here in Middletown we have some squirrel variation that invites greater appreciation. Of course I’m referring here to the beautiful jet-black squirrels that frolic and scavenge about the Wesleyan campus.
The black squirrels often surprise newcomers. But they are just “a melanistic subgroup of the eastern grey squirrel,” as Wikipedia has it. They are fairly plentiful in Middletown, but I found some old letters written to the Hartford Courant that seem to suggest that this was not always the case. In one letter, written in October 1923, the writer remarks that the black squirrel in Connecticut “must be very rare.” He then goes on to say that in Ohio and Northern Wisconsin they are very common. These locations are near Ontario, where the black squirrel has apparently been abundant for decades. Another letter to the Courant, this one written in December 1971, mentions a “black squirrel shot near Bradley field.” This letter suggests that the black squirrel is not so rare. It also says that the town of Westfield, Massachusetts has “a good-sized colony of black squirrels.” This is, admittedly, limited evidence—and hearsay besides—but it would not be out of the question that the black phenotype has been on the rise in these parts.
This claim is backed up by a radio story from North Country Public Radio, which alleges that the black subgroup of the eastern grey squirrel species is becoming more common in the Northeast. We are not sure exactly why this is, but perhaps Jolly Old England would be a good case study: Early in the 1900s grey squirrels were brought to England and pushed some of the native squirrels out. Recently black squirrels were introduced there from North America, and now have been outperforming grey squirrels. So what is it about black squirrels that gives them the evolutionary edge?
In evolutionary biology there is a story of “peppered moths,” which have a grey version and a black “sooty-colored version.” It’s a classic story of natural selection in the wild. (By the way, this is all from that radio program.) The phenomenon is called “industrial melanism.” In England in the 1800s, during the Industrial Revolution, there was a good deal of air pollution and factory soot. The trees downwind of factory towns became black and sooty, giving the advantage to the black moths, which had better camouflage, and so their population rose and outdid the grey moths.
So could something like this be an explanation for the squirrels? Probably not, given that the grey moths are coming back now that the Brits have stopped wholesale blackening the forests. According to homefacts.com, Middletown has good air quality (it says that 91.08% is good, to be specific), and according to my eyes the air isn’t black, so it probably has nothing to do with pollution, and possibly the black trait is not adaptive.
In any case, at some point there was a mutation that gave some squirrels black fur, and for some reason they became relatively successful in certain areas. Then perhaps they were introduced to other areas, or just spread there naturally. They belong to the same species, so when black squirrels get with grey squirrels, or other black squirrels, fertile baby black squirrels result, sometimes in mixed litters with other colors. Perhaps these days the grey squirrel has a greater advantage camouflage-wise, but in urban areas where large predators are driven away by human activity the black squirrels could just as easily flourish.
Or, perhaps greater visibility has actually helped them—bear with me here—because they are more easily seen and avoided by motorists! Nope. According to an article in the Washington Post, they “found no discrepancy in the squash rates of black vs. gray squirrels.”
The mystery! The intrigue! The more I look into this, the more I’m fascinated. This is my favorite theory that I found: Apparently the thing that might be giving black squirrels the edge, according to the aforementioned radio story, is that the males seem to have more testosterone. Probably a female squirrel is more willing to get with the squirrel that has higher testosterone levels given that he works out and drives a sweet car. Also, picture this: A grey squirrel approaches a nut—possibly one that struck someone’s head outside of WesWings—and then a black squirrel approaches and makes angry squirrel noises. In this situation the grey squirrel is more likely to back off, owing to its lowered levels of aggressiveness. Long story short, the black squirrel appears more able to protect its nuts. No pun intended.
I put some of these questions, plus a few crack theories of my own, to Michael Singer, a Professor of Biology and Environmental Studies, an expert in things like evolution and ecology. His answers were somewhat sobering. For one thing, my favorite theory, the theory of testosterone levels, is unlikely unless the black color is a sex-linked trait, meaning found only in the males. Which it is not. So that’s that. Furthermore, according to Prof. Singer, transplantation of the squirrels seems to be the least likely explanation.
The explanation that Prof. Singer sees as most plausible is random mutation and relaxed natural selection against the black phenotype. He says it best himself:
The black color is most likely the result of a mutation, which probably occurred by chance (as most mutations do). Without a scientific study, it is impossible to determine if the black phenotype is adaptive or not. My guess is that it is not adaptive (conferring a reproductive advantage), but that selection against it is weaker in the campus population versus other populations. The most likely selection pressure on squirrel color would be from visual predators, such as hawks. While hawks do occasionally kill squirrels on campus, they probably don’t kill them as often as they do in other places. (Hawks don’t like to hang around people very much.) On campus, the hunting challenge for a hawk wouldn’t be visually detecting a squirrel (as it might be in a natural forest), but rather finding an opportunity to attack when people aren’t around. Therefore, hawk predation is likely to eliminate black phenotypes from most squirrel populations, but the campus environment probably relaxes that selection pressure.
This seems pretty solid, albeit somewhat anticlimactic. The truth is often so. The one thing that leaves it open for me, however, is the prenominate Washington Post article. It alleges that their population of black squirrels came from a batch of eight black squirrels, given to them by Canada to the National Zoo. So there is a precedent of this, and the ultimate explanation could be a combination of these two things: introduction and the relaxed selection pressure against the black trait around our community. I’m not saying we got black squirrels imported specifically into Middletown; I just mean that maybe the black squirrels in Middletown have some imported great-great-great-great–how long do squirrels live?–great-great-grandparents whose progeny traveled to Middletown in search of a better life and unsuspecting students to pelt with acorns.
It is very possible that I’ve missed some articles in peer-reviewed science journals, but it seems that the answers I’ve found are ambiguous. And it seems odd that these little creatures, things we see every day, are the subjects of such uncertainty. They are too close to us for us to truly look at them—we take them for granted—they are staples of our everyday experience, and yet we don’t truly see them. They flicker in and out of our periphery, playing with each other and gathering nuts and chasing us (that happened to me once), and yet we have no certainty as to why there are so many of them here and not, say, Seattle, where I’m from. I guess that something to take away from this is that the human encroachment on squirrels’ habitat, which I mentioned before quite negatively, is actually the reason there is more squirrel diversity; otherwise they’d be easy pickings for their airborne predators. You’re welcome, black squirrels.
But this whole thing has sort of turned into an epistemological nightmare that I need to tangle through after some serious meditation. I just don’t even know what to believe anymore. Jesus, is this what journalism is?