The Grey Squirrel is perhaps our most familiar mammal, an introduced species that has adapted well to the opportunities on offer within gardens and the wider British countryside. Not always welcome, the Grey Squirrel is resourceful and can become a nuisance at garden feeding stations where it quickly learns to take advantage of seed and other foods put out for birds.
Grey Squirrels are known to carry the Squirrel Parapox Virus, to which they have been demonstrated to have some clinical resistance. The disease is thought to pose a serious threat to our remaining Red Squirrel populations and strategies are in place to limit this threat.
Grey Squirrels may cause economic damage to forestry but are welcomed by many as one of the few approachable mammal species within Britain. The sight of a Grey Squirrel in an urban park may provide a rare opportunity for a child to engage with the natural world.
Although predominantly grey in appearance, some individuals may show a warm brown colouration across their flanks and back. Some populations have individuals that are black (melanic), e.g. in parts of Hertfordshire, and occasional white individuals are not unknown. Juveniles are a darker grey than adults. The Grey Squirrel is larger than our native Red Squirrel and, therefore, less agile and unable to forage on the smaller branches of trees.
This native of North America was introduced into Britain from the 1870s onwards to several dozen different sites. Rapid expansion then followed and the species is now established across most of England and Wales, much of the Central Belt in Scotland and a good part of Ireland.
A wide range of habitat types is used, from mature broad-leaved woodland to conifer plantations, urban parks and gardens with mature trees. The association with woodland and mature trees reflects a diet dominated by tree seeds and other plant material but the species will also scavenge at bird tables and is known to take the eggs and young of birds.
One of the characteristic behaviours of autumn is the caching of food items, especially acorns. The Grey Squirrel has been found to cache those acorns that keep well, eating others that have a short shelf-life, perhaps because of damage to the seed coat.
Female Grey Squirrels can have two litters each year, one in the spring and one in the summer. Each litter contains 3-4 young. Grey Squirrels can breed from as young as 10-12 months.
The use of gardens by Grey Squirrels appears to be fairly consistent throughout the year, with a suggestion of a slight increase during the summer months. Interestingly, the initial data coming in for 2012 show an increased use of gardens this year, the reporting rate increasing from the end of the first quarter and, by autumn, reaching a level well in excess of previous years.