I’m surrounded by forest ninjas.
They’re stealthy, incredibly agile, and like all ninjas, they excel at their craft—in this case, larceny from my neighbors’ bird feeders. Our woods are full of them.
I’m talking about jet-black, bushy-tailed tree rodents, the local teenage mutant ninja squirrels. They’re not all teens, of course. But every one of them is indeed a mutant.
The ninjas are eastern gray squirrels with a mutation that causes them to make too much dark pigment. Scientists call them melanistic-phenotype squirrels. The same mutation exists in eastern fox squirrels, whose range is similar to the eastern gray.
Dark fur is believed to hold heat better than gray or red fur, a survival advantage in northern climates. Generally, the black morphs make up just one percent of the eastern gray squirrel population. Their black fur’s added warmth might explain these squirrels’ large numbers in areas of Michigan and eastern Canada—up to 75 percent of the eastern gray squirrel population in some northern parts of their range.
Watching their antics this week, I wondered why black squirrels are also abundant in some cities with milder climates. I saw lots of them as a tourist in Washington, DC . They seemed to be everywhere in Kent, Ohio, where I lived for a year.
It didn’t take many mouse clicks to learn that mutant ninja squirrels are migrants, too—with help from humans.
In 1902, eight Canadian black squirrels were brought to Washington, DC at the request of the superintendent of the National Zoo. Their descendants now account for about a quarter of Washington’s squirrel population. In Ohio, the head groundskeeper at Kent State University imported black squirrels from Canada in 1961. Today they’re quite visible on campus and in town. My area’s melanistic squirrels have managed some rides, too. Newspaper stories tell of visitors bringing west Michigan’s black squirrels to Ohio, Illinois, Indiana, Massachusetts, and Maine.
They’ve even crossed the ocean. Sometime in the early 1800’s eastern gray squirrels, apparently including some melanistics, were brought to England as fashionable additions to country estates. Unfortunately, the grays have replaced many of the native red squirrels. That’s mostly because the grays can survive a virus (yes—a virus!) called squirrel pox, which is fatal to the reds. The black morphs have similarly multiplied. Today, there are some 25,000 black squirrels in the UK, concentrated in eastern England.
You may see a sprinkling of black squirrels here and there. Scientists believe that habitat change helps the melanistics gain ground in the general squirrel population. As forests mature, the tree canopy grows denser, creating more shade and shadows. Black fur blends into dark areas better than gray or red, offering added protection from predators.
Now, for my usual blog video. I chose a clip showing black and gray squirrels, face-to-face. The black squirrel looks young to me (I’ve watched quite a few squirrel nests and youngsters). And its behavior is a bit comical. See what you think:Unlike their cartoonish turtle counterparts, my neighborhood ninjas haven’t earned the rank of superhero. But they are super cute! Have you seen any teenage mutant ninja squirrels in your neck of the woods?
You might enjoy some of the articles I read to learn about black squirrels:
A fun article about Canadian squirrels going to Washington, DC
Black squirrels in Kent, Ohio with a discussion of habitat change’s influence on black squirrel population growth.
Gray squirrels in the UK with a discussion of squirrel pox and the demise of the native red squirrel population.
Image Credits: Carol Doeringer.