Photo by Flickr user audreyjm529 

“Can you find out if there are black squirrels all over Northwest DC because a pack of rare black squirrels from Canada escaped from the National Zoo?”—Chris Billeter

The National Zoo received black squirrels from Ontario’s Department of Crown Lands in 1902 and 1906 and released 18 into the northwest corner of the park. At the time, zoo officials intended for the squirrels to be an attraction for visitors and didn’t realize they’d move into the city.

Since then, black squirrels have become part of Northwest DC’s squirrel population, which is slowly spreading to other regions in Washington. “When I moved to Bethesda in the 1970s, black squirrels were in our immediate neighborhood, but they were never seen outside the beltway,” says Richard Thorington, curator of mammals for the National Museum of Natural History. “Then, in the 1980s, people in Virginia said they were seeing them in their backyards.”

Thorington, who wrote a book titled Squirrels: The Animal Answer Guide, says one of the reasons for the growing number of black squirrels is a gene that affects their pigmentation and makes them black.  The zoo officials who had the original 18 black squirrels didn’t realize that this gene was dominant when they released them into the zoo.

Although the gene is dominant, the number of black squirrels in the overall squirrel population is never more than 25 percent for any one area. No one is sure why, though Thorington speculates that it has something to do with the black squirrels’ tendency to attract more predators: “Since black squirrels are more conspicuous than gray ones, they stand out more,” he says.