February

Grey squirrel (Sciurus carolinensis)

The grey squirrel was introduced into this country from North America on a number of occasions between 1876 and 1929, and is now widespread in all areas except for parts of northern Scotland. It is also present in the eastern half of Ireland. It continues to spread into these uninhabited areas despite efforts to stop it doing so, and now has an estimated UK population of two and a half million.

Squirrels can be seen throughout the year and do not hibernate, as some believe, but will occasionally “lie up” in particularly cold and inclement periods of weather. They are a diurnal species which appears to be as much at home in our towns and cities as they are in rural areas. They share home ranges with other squirrels and are not territorial, observed skirmishes usually involving males chasing females or a perhaps a brief tiff over food. Grey squirrels build substantial nests called dreys, often cutting growing small branches and leaves straight off the tree to construct the domed nest, which they position high up in a fork, often against the tree trunk. In older woodland, many squirrels will use holes in trees rather than constructing dreys.

Holes and dreys are used both for lying up in and for rearing young, although the breeding drey tends to be a more substantial construction than the more flimsy resting nest. The young, known as kittens, are born in early spring and usually number between 3 or 4, although occasionally up to 6 or 7 can be born. The kittens are born after a gestation period of 44 days and are completely blind and hairless, feeding on milk until being weaned at around 8 to 10 weeks of age. In the majority of years a second litter is produced later in the summer and young squirrels can start to breed themselves from around 10 months old.

Grey squirrels have many faults which make them unpopular, such as raiding bird tables to empty unguarded nut or seed feeders, eating nuts from bushes well before they are fully ready to be harvested and also in showing a penchant for small birds’ eggs and nestlings. But it is their habit of stripping the bark from trees, in particular beech and sycamore, to get at the fleshy green wood underneath that means they are particularly disliked by foresters. This habit can at worst kill trees, but more often it distorts growth and affects the quality of timber being grown, eventually resulting in a poorer harvest.

Another unpopular trait of the grey squirrel is that they carry the “squirrel parapox virus”. Grey squirrels themselves have built up antibodies against this, but it can be easily passed onto our native red squirrel which has no such immunity and will die within a week of being infected. This virus, coupled with competition for food in mixed woodland, has made our native squirrel something of a rarity. There are various groups employing much time and effort to halt the march of the grey squirrel, but often with little success. One of the most successful eradication efforts was on Anglesey where more than 6,000 greys were killed allowing red squirrels to increase once again. Eradication of a given population is always more practical on an island however, the mainland being a different proposition all together.

The range of problems posed by the non-native grey squirrel led to the foundation of the European Squirrel Initiative in June 2002 - foresters and conservationists from across Europe combining forces to tackle the various detrimental impacts that this species is causing. But they may not have it all their own way as a survey in 2002 by the Mammal Society indicated that 45% of people liked grey squirrels, while only 24% actually disliked them.

Then of course there is the issue of colour! Black “grey” squirrels are now colonising parts of East Anglia, especially around the counties of Cambridgeshire and Bedfordshire, and have already grown to a population estimated to be at least 25,000. By all accounts the locals think that their black squirrels are rather special, giving yet another item on the agenda for the European Squirrel Initiative to discuss!

Peter Thompson
Advisory

Read more from Peter Thompson at the Fresh from the Field blog.