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Black squirrel 'super' species? No, just a darker shade of grey

The Guardian logo The Guardian 13/08/2019 Patrick Barkham
a squirrel standing on grass: In Britain, black squirrels were imported from North America and then escaped from private zoos. © PA In Britain, black squirrels were imported from North America and then escaped from private zoos.

In popular myth they are an aggressive new “super” species pushing out the grey squirrel just as it has displaced the red squirrel.

But the black squirrels seen scampering through southern England are a form of grey squirrel created by wild interbreeding between greys and fox squirrels in North America, according to research.

Black squirrels are the same species as the grey but acquired their coat via a faulty pigment gene identical to that found in the fox squirrel, a closely-related species which is also native to North America and has black variants.

Dr Helen McRobie of Anglia Ruskin University worked with colleagues from the University of Cambridge and the Virginia Museum of Natural History in the United States to test DNA from grey and fox squirrels across North America.

Black squirrels are the same species as the grey one Black squirrels are the same species as the grey one

They discovered that other “signatures” on the mutated gene are more closely related to the fox squirrel, suggesting it is highly likely the mutation first arose in the fox squirrel and passed to the grey through interbreeding.

Dr McRobie said the most likely explanation for the black version of the gene being found in the grey squirrel was the result of a black fox squirrel joining a grey squirrel “mating chase” and mating with a female grey.

She added: “The fact black grey squirrels have become so common right across North America is possibly because black fur offers a thermal advantage, helping them inhabit regions with extremely cold winters. This may have contributed to the expansion of the grey squirrel’s range during the past 11,000 years, following the end of the most recent ice age, helping them spread further north into Canada.”

In Britain, black squirrels were imported from North America and then escaped from private zoos. The first was spotted near Letchworth in 1912 and black squirrels are today most commonly sighted across Hertfordshire, Bedfordshire and Cambridgeshire.

The spread of grey – and black – squirrels has caused the extinction of red squirrels in much of England because the native reds succumb to the squirrelpox virus, which is carried by greys but leaves them unscathed.

Gallery: 15 Squirrel Facts for Squirrel Appreciation Day (Mental Floss)

Another study in which grey squirrels on the Wirral were tested for squirrelpox every month has found that greys survive in the wild even when carrying the virus for months.

Prof Julian Chantrey and colleagues at the University of Liverpool tested more than 100 grey squirrels over a 16-month period. In research published in the journal Epidemics, they found the squirrelpox virus in more than 80% of grey squirrels, with greys repeatedly reinfected with the virus.

Chantrey said: “It shows that the virus is very widespread and greys are at a very high risk of introducing pox to red populations.”

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