Tuesday, August 5, 2014

Black Gray Squirrels?

Black colored Gray Squirrel

     I have been asked many times by people about the black squirrels we have in the DC area. Though they are actually just melanistic versions and the same species (Scirius carolinensis) as the regular Northern Gray Squirrels, they actually have an interesting history behind them. I thought a little bit of natural history history might interest folks.

Northern Gray Squirrel, the typical backyard squirrel around here

     As I stated before, the black squirrels are actually the same species as the normal backyard squirrels we have all around and can freely interbreed with them. They were purposely reintroduced, along with the "normal" gray squirrels, back into the DC area in the early 1900's after there was concern that there wouldn't be any squirrels of any type around any more locally, that they had been close to being extirpated. Gray squirrels were indeed very rare, having been mostly hunted out long before. By 1906, hunting was prohibited within the city and people wanted to bring them back, believing they would be great additions to parks. 
     So gray squirrels were released at several DC parks such as Lafayette Park. They were fed by people and even by Park Police. Teddy Roosevelt, who had quite a menagerie of pets anyways and loved squirrels in general (he had flying squirrels at his cabin for instance), had them released at the White House in 1907 as well. A great movement to reintroduce them was succeeding.

Both a normal gray and black gray squirrel share a tree in Arlington, Virginia.

     But what about the black squirrels? These may also be a result of Teddy Roosevelt. It seems that in both 1902 and 1906, 18 black squirrels were brought to the National Zoo from Ontario, Canada. Black squirrels are much more common there, likely because the dark color gives them a heat advantage that offsets any disadvantage from their not being able to hide as well. These 18 dark squirrels were released from the zoo sometime after 1906. By 1917, the first road kill of a black squirrel was recorded. 
     So the National Zoo became ground zero for these darker squirrels. Since there were not as many "regular" gray colored squirrels and the black ones may have had a heating advantage (and no predators were around to hunt them), the recessive dark genes were allowed to establish themselves in the population. Now almost half the squirrels around the zoo are black or darker in coloration.
     Being protected and well fed, squirrel populations exploded. In fact, a 1980's study resulted in the claim that no where else on earth were there squirrels more densely populated than Lafayette Park. The black squirrels also continued to spread, by the 1980's being found in some numbers in Arlington, Virginia and parts of Maryland. Now up to a fourth of the squirrels in these locations are dark. 
     Squirrels are of course rodents, and breed as fast as many rodents do. They have spread and their numbers now can be quite abundant. "Tree rats" in fact have been declared one of the top 100 world's worst invasive alien species by the World Conservation Union, causing issues in places such as Great Britain and other parts of Europe where they do not belong. Time Magazine listed them as one of the top 10 most invasive animals in 2010. Yet while some bird feeders and gardeners in the USA also wage their wars on squirrels, many other people thoroughly enjoy them. They have become regular features of our neighborhoods despite their rarity a century ago. 

This black gray squirrel appears to be lactating and so appears to be raising more squirrels. Each litter may contain both black and normal colored gray squirrels. 

     From ground zero at the National Zoo, the black squirrels continue to spread into the surrounding region. Sometimes they endear themselves, other times they are hated, but mostly they are just ignored. They are with us to stay all the same. Hard to believe how it all started, with the 18 black ones released during the Roosevelt administration. I thought it would be interesting to end with a squirrel mating chase led by a female black squirrel literally playing hard to get to test which of her suitors is the most fit:


No comments:

Post a Comment