Grey squirrels (Sciurus carolinensis) are one of the most common species of tree squirrels found throughout much of the eastern United States. As their name implies, grey squirrels typically have thick fur that is predominately grey in color. However, some individuals may exhibit black or albino color variations.
What causes black color variations in grey squirrels?
The black color variation found in some grey squirrels is caused by increased levels of the melanin pigment in their fur. Melanin is the primary pigment that determines fur color in mammals. Increased melanin leads to darker fur colors, while decreased levels cause lighter fur colors.
There are several potential mechanisms that can cause increased melanin production in grey squirrels:
- Genetic mutations – Random mutations in genes involved in melanin synthesis may lead to increased melanin levels.
- Chimera – Some black squirrels may be chimeras, meaning they have two sets of DNA if two embryos fused together. This can cause unusual pigmentation.
- Disease/parasites – Certain diseases or parasites may trigger greater melanin synthesis.
- Age/seasonal changes – Melanin levels may increase with age or seasonal changes.
Most often, the black color variation arises randomly due to genetic mutations that get passed on within isolated local populations. The mutation gets maintained if it does not negatively impact the squirrel’s survival.
Where are black grey squirrels found?
Black grey squirrels can be found scattered throughout the grey squirrel’s native range, but certain geographic regions have higher proportions of black squirrels:
- Parts of Canada – Large populations of black grey squirrels are found in some areas of Eastern and Central Canada.
- United Kingdom – When grey squirrels were introduced to the UK from North America, some black ones were inadvertently brought over as well and proliferated.
- Midwestern United States – States such as Ohio, Michigan, Wisconsin, and Minnesota have significant black squirrel populations.
- East Coast – Scattered populations of black grey squirrels are found along the East Coast from New York to Florida.
In areas where they occur, black squirrels appear to thrive just as well as their grey counterparts.
Are black grey squirrels a separate species?
No, black grey squirrels are not a distinct species from regular grey squirrels. They belong to the same species, Sciurus carolinensis. The main difference is a genetic variant that causes increased melanin production.
Black and grey squirrels can interbreed and produce viable offspring. Their behavior, diet, habitat, and ecological roles are identical. The only noticeable difference is their fur color.
Some people refer to black grey squirrels as “melanistic grey squirrels” to emphasize that they are genetically similar with a color variant. But most people simply call them “black squirrels.”
Are black grey squirrels rare or endangered?
In most areas, black grey squirrels are relatively rare compared to their grey counterparts. However, in certain regions with higher proportions of black squirrels, they are quite common and not considered rare or endangered.
For example, black squirrels make up about 25% of the squirrel population in Toronto. In the UK, approximately 25% of grey squirrels have black fur. In areas where they are well-established, black squirrels are not at any conservation risk.
However, in small isolated populations, black squirrels may be threatened due to lack of genetic diversity combined with competition from larger grey squirrel populations. Local efforts may be needed to conserve isolated black variant populations.
Do black squirrels behave differently?
There is no evidence that black grey squirrels behave significantly differently from grey squirrels. Their activity patterns, social behavior, breeding behavior, and habitat usage appear to be identical.
Both color variants construct nests called dreys in trees, mate twice per year, gestate young for about 44 days, and eat similar foods like tree seeds, fungi, insects, and fruit. Neither color variation is more aggressive or dominant.
The main observable difference is that black squirrels tend to be more wary and less likely to approach humans. But this likely reflects differences in local urbanization levels rather than innate behavior differences.
Are black squirrels smarter?
There is no scientific evidence to suggest that black grey squirrels are smarter than their grey counterparts. Both variants appear to have very similar brain size and neural anatomy.
Grey and black squirrels exhibit comparable complex behavior when it comes to navigation, food caching, predator avoidance, tool use, and communication. Differences in local urbanization may lead to subtle differences in problem-solving skills when interacting with humans.
In one study, black squirrels showed greater problem-solving efficiency in a laboratory setting. But scientists concluded this was likely due to higher wariness rather than greater intelligence.
Overall, both grey and black color phases seem equally intelligent and adaptable in utilizing their environment to survive and thrive.
Do black and grey squirrels get along?
In areas where they coexist, black and grey squirrels appear to get along without serious conflict or competition. They often form mixed social groups with both color variants.
There is no clear dominance or aggressive behavior between the color phases. Black and grey squirrels have even been observed nursing each other’s young in communal nests.
The two variants will also mate with each other fairly regularly. Within the same litter of baby squirrels, some may be black while others are grey.
However, in very rare cases, intense competition for resources in overcrowded urban environments has caused grey squirrels to chase out black variants.
Do predators target black squirrels?
Some people hypothesize that black squirrels may be targeted more frequently by predators, but there is little evidence to support this.
Potential squirrel predators like hawks, coyotes, foxes, bobcats, and weasels rely more on eyesight, hearing, and smell to hunt rather than coat color specifically. Camouflage is not a primary defense for tree squirrels.
One study in Kansas found that predation rates were nearly identical between black and grey squirrel populations in the same habitat. Both variants seemed equally successful at avoiding predators.
In some cases, the wariness of black squirrels near humans may actually decrease their predation risk in urban areas since they spend less time on the ground.
City | Black Squirrel Percentage |
---|---|
Toronto | 25% |
Detroit | 10% |
Kent | 50% |
Philadelphia | 20% |
Conclusion
In conclusion, black grey squirrels represent a color variant of the common eastern grey squirrel caused by increased melanin levels. While they can appear in any grey squirrel population, black squirrels seem most prevalent in certain regions of Canada, the Midwest, and the UK.
Aside from fur color, black squirrels exhibit nearly identical behavior, intelligence, and ecological roles as greys. The two color phases get along well for the most part and regularly interbreed. Neither variant seems clearly advantaged or disadvantaged in the competition for resources.
So in most respects, black eastern grey squirrels remain biologically similar to their grey counterparts, with coat color being their most distinctive attribute.