The Grey Squirrel (Sciurus carolinensis)

The grey squirrel was introduced into Britain in the late 1800s and has proved to be a major ecological disaster ever since. The native animal to suffer most from the grey’s introduction is the red squirrel. The grey has largely supplanted the native red in England and Wales. In Britain it is estimated that the greys outnumber the reds by 66 to 1. In Europe they are also discovering what a destructive creature the grey squirrel can be.

Grey squirrels are detrimental to the reds’ survival for two reasons. They outcompete the reds for food and they are a carrier of the squirrelpox virus which results in a painful death for the reds. When competing for food, the greys appear able to exploit food sources much more efficiently, and at an earlier stage than the reds, so by the time the reds consider something to be edible, it has already been taken by the greys, eg. hazel nuts.

It is generally accepted that on average, one hectare of woodland will support one red squirrel weighing 300 grams or 16 grey squirrels weighing 600 grams each.. So, if only one grey squirrel was occupying a hectare of woodland, its survival would not be threatened if another 15 grey squirrels moved into the wood. However, if a red squirrel were occupying a hectare of woodland and just one grey squirrel arrived, it would severely impact on its ability to find enough food and to breed. This is one of the reasons why even just small numbers of grey squirrels can tip the balance.

Grey squirrels inflict a terrific amount of damage on Britain’s timber crop, either by ring-barking, where the tree dies, or by bark-stripping, which can leave the tree prone to disease. There are now calls for a study into the role of grey squirrel into the decline of our woodland birds. Grey squirrels are known to take the eggs and young of woodland birds and it seems logical that the birds and their young in a one hectare wood, are going to suffer more from the presence of 16 grey squirrels wrighing 600grams each than that of one timid 300 gram red.

Grey/brindle in colour. At approximately 600 grams they are twice the size of the red squirrel. Regularly breeds twice a year with an average of three young per litter. Greys live until the age of 8 or 9 years. On occasions have been known to attack and kill red squirrels