The rise of the interbred black squirrel

Black squirrels in the UK

The rise of the black squirrel in the United Kingdom has since been mapped by Dr Helen McRobie in 2014. Dr McRobie has recently built on the study with some new finding on the origin of the black squirrel in the UK.

Black squirrels are the same species as grey squirrels. The only difference between the two is that they have different coloured fur.

Scientists believe that the different coloured fur is due to a pigment gene with a missing piece of DNA. This grey squirrel gene fault is the same as that of a faulty-gene found in it’s relative, the North American fox squirrel.

Fox squirrels have the same black variant. This is believed to have a direct connection to the spread of black squirrels in the UK.

Rigorous DNA testing of both grey squirrels and fox squirrels has been conducted over the United States and British Columbia. The research was undertaken by Dr Helen McRobie, the University of Cambridge and the Virginia Museum of Natural History.

The mutations are believed to be a result of interbreeding between grey squirrels and fox squirrels.

The first instance of said interbreeding in the UK can be traced back to around 1912 when a scurry of black fox squirrels escaped a private zoo in Woburn, Bedfordshire.

Dr McRobie, Senior Lecturer in Biomedical Science at Anglia Ruskin University (ARU), said: “Squirrels take part in ‘mating chases’ where a female squirrel is pursued by lots of male squirrels and eventually one male mates with the female.

“People have spotted ‘mixed species’ mating chases, with a mix of grey and fox squirrels pursuing a female. The most likely explanation for the black version of the gene being found in the grey squirrel is that a male black fox squirrel mated with a female grey squirrel.

“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.”

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  1. Having visited relatives in Hamilton Ontario, I was intrigued to see black squirrels in their garden. I’ve often pondered on this so was most interested to read this article about their appearance in the UK and their origins. Thanks!


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