In the U.K., the grey squirrel has long been demonized as a non-native invader that has pushed the once widespread red squirrel to the brink of extinction in the British Isles. But new research suggests that the fluffy-tailed rodents are not to blame for their own rapid expansion across the country, and that humans are actually the ones who moved them around and transported them to the far reaches of the nation.
The grey squirrel’s quick spread across England after being introduced from North America in the 1890s has come to exemplify the threat faced by invasive species. This is often held as a common example of how non-natives can rival resident species, as the bigger and more aggressive greys outcompete and replace the smaller reds, while also harboring deadly diseases (such as squirrel pox) that only affects the natives.
But after genetically testing over 1,500 greys from across the U.K., and also in Italy where they have been introduced, the researchers found that the rodents might not be as good at invading new patches as was previously thought. The DNA results showed that groups of greys and reds that were bordering each other were surprisingly isolated, suggesting that little mixing occurs between them. In addition to that, they also discovered that some grey populations hundreds of kilometers apart were more closely related than those next door.
The native red squirrel has been pushed out of most of England, although they are surviving in northern Scotland. seawhisper/Shutterstock
This, they suggest, shows that the spread of the squirrels was actually far more likely to have happened due to humans moving them around, and they even pinpoint one of the worst culprits: The 11th Duke of Bedford, Herbrand Russell, was particularly fond of the then-exotic greys. The once-President of the Zoological Society of London gifted many of the animals around the U.K., and even released a population of them into Regent’s Park, London. The researchers think that while humans helped them spread, it was their aggressive behavior that then took over and helped them establish breeding populations.
“Grey squirrels are not as crazy invaders as we think – their spread is far more our own fault,” says Dr. Lisa Signorile, who led two studies on the subject published in two journals, Biological Conservation and Diversity and Distributions. “It has been thought since the 1930s that grey squirrels were all the same, spreading across the country as one invasion front. After a century, genetics has proved that this isn't correct. They are not that good at breeding and mixing – in fact there are clear signs of inbreeding.”
Interestingly, this dispersion by humans hasn’t actually stopped. In one case recorded by Dr. Signorile, she found a squirrel on the remote Scottish Isle of Skye that had actually come from Glasgow, over 370 kilometers (230 miles) away. She suspects it probably hitched a ride under the bonnet of someone’s car. The researchers hope that this new study could help better develop new strategies to tackle their numbers in the U.K. Currently, a lot of effort is spent on reducing their numbers, with no thought going into how to prevent their movement or discouraging people from picking them up.