Black squirrels, with their striking dark fur, are a common sight in many regions. These distinctive animals are not a separate species but a color variation of more common squirrel types. Their presence in parks and urban environments highlights a unique genetic story.
What Makes a Squirrel Black
The black coloration in squirrels results from melanism, a genetic condition involving an overproduction of melanin, the pigment responsible for dark hues. Black squirrels are primarily a melanistic variant of the Eastern Gray Squirrel (Sciurus carolinensis) and, less frequently, the fox squirrel (Sciurus niger).
The genetic basis for this dark fur in Eastern Gray Squirrels is a particular mutation involving a 24 base-pair deletion in the melanocortin 1 receptor (MC1R) gene, specifically known as the MC1R∆24 allele. This allele is considered incompletely dominant. A squirrel inheriting one copy of this allele will display a brown-black coloration, while those with two copies will exhibit a jet-black coat. Research suggests this variant gene likely originated in fox squirrels and was later introduced into the Eastern Gray Squirrel population through interspecies breeding.
Their Origins and Distribution
Black squirrels naturally occur across North America, within the native ranges of both the Eastern Gray Squirrel and the fox squirrel. While present throughout these areas, their frequency varies significantly by region. They are most commonly found in the northern parts of the Eastern Gray Squirrel’s range, particularly around the Great Lakes Basin. This includes regions such as Ontario and Michigan, where black morphs can constitute the majority of the squirrel population. Significant populations also exist in parts of the Northeastern United States and northern Ohio.
Beyond their native North American range, black squirrels have also been introduced to other parts of the world, notably the United Kingdom. These populations typically originated from North American black squirrels brought over during the 19th and 20th centuries. The first recorded wild black squirrel sighting in the UK occurred near Woburn in 1912, with these animals believed to have escaped from private zoos or collections.
The Advantages of Being Black
The black coloration in squirrels offers several potential ecological advantages, particularly in certain environments. One significant benefit is improved thermoregulation, especially in colder climates. Darker fur absorbs more solar radiation, which helps the squirrel retain heat, providing a survival advantage during harsh winters. Studies have indicated that black-coated squirrels may experience lower heat loss and reduced metabolic rates in freezing temperatures compared to their lighter-furred relatives. This thermal benefit may contribute to increased activity during colder periods, such as winter mornings.
Additionally, the dark fur can provide camouflage benefits. In densely shaded forests or urban areas with dark surfaces, the black coat can help these squirrels blend into their surroundings, potentially offering concealment from predators. Historically, black squirrels were more prevalent in North America’s old-growth forests, where their dark coloration was advantageous in the dim, dense undergrowth.