Species of the day: Grey Squirrel

08 April 2020 | Posted in James Duncan , mammals
Species of the day: Grey Squirrel
Grey Squirrel © James Duncan

By James Duncan

Learning and Engagement Officer

There probably couldn't be a more contentious animal amongst UK wildlife than the Grey Squirrel (Sciurus carolinensis). On the one hand it's a rodent invader from the other side of the Atlantic, one that causes damage to sensitive woodland ecosystems and heavily contributes to the declining population of native Red Squirrels (Sciurus vulgaris). On the other hand, it's been fully naturalised since the late 1800s and offers people living in urban areas a considerable opportunity to connect with nature. It's a conundrum for sure, one that continues to divide opinion up and down the country. Of course it's by no means our only naturalised mammal - four of our six deer species and even Rabbit, Brown Hare and Edible Dormouse have their origins elsewhere.

Humans have ultimately enabled the rapid spread of the wily Grey. There are certainly a multitude of well-documented releases at the beginning of the twentieth century - these occurred when our knowledge of the devastation wreaked by invasive species wasn't well understood. For nearly one hundred years it's been thought the squirrel's supreme adaptability to new environments has enabled its spread. However, a genetic study carried out in 2016 by Imperial College London and ZSL indicates that they may not be quite as adept at invading as we once thought - many have expanded from either small pockets of initial releases or have been unwittingly transported to new locations. Populations are typically genetically distinct, demonstrating that squirrels living in close proximity may in fact have originated from a long way away. Whatever the reasons, the fact remains there's an estimated 2.5 million in the UK. Without many natural predators, the larger and tougher Grey not only outcompetes the Red, but may also transmit Squirrelpox (SQPV) to which it is immune. This leads to the Greys ultimately replacing the Reds in shared environments.

Controversy aside, Grey Squirrels are of course master acrobats. Their agility, balance and finesse have few equals in the animal kingdom. They're strong runners and use their bushy tail as a method of directing and carefully adjusting their trajectories when airborne. They display an innate ability for quick learning and as a rule it won't take them long to work out how to raid your garden bird-feeder. They'll carefully cache seeds and fruits to ensure survival in winter, though they're smart enough to realise there's not much honour amongst their own kind - theft is rife and they often pretend to bury nuts in order to throw others off the scent. Of course burial locations aren't always remembered, helping to enable the spread of new trees. They construct a nest known as a 'drey,' though don't actually hibernate. In fact our mild climate leads to Greys being relatively active all year round - their feisty antics can be witnessed pretty much wherever you go.   

Grey Squirrel1 © James Duncan

Grey Squirrel © James Duncan

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