Family: Scuiridae - Squirrels
Phylum: Chordata - Vertebrates
Red List status: Least Concern
Body length: 230-400 mm
Tail length: 195-250 mm
Weight: 400-700 g, normally 450-650 g
Eastern North America from Manitoba in Canada to Florida in the southern United States. Populations have been successfully introduced to urban areas of the western US, Italy, South Africa and the United Kingdom. In the UK, the species now occurs throughout the British mainland and in areas of Northern Ireland.
A moderately large, robust squirrel with dark reddish-brown to grey body and tail; very occasional melanistic or albino forms may be encountered. The head is often reddish-brown. The underparts are white.
Similar species: In Europe, introduced populations may co-occur with the red squirrel (Scuirus vulgaris). The red squirrel is smaller, more slender in build, and exhibits long tufts on the ears in winter; grey squirrels have short tufts which may not be apparent. Red squirrels are considerably more variable in colouration from black through brown to red, but are never grey. The North American fox squirrel (Scuirus niger) is larger and often brown or black. In some regions grey forms of the fox squirrel occur, but has yellowish rather than white underparts.
Naturally favours deciduous and mixed woodlands; now commonplace in gardens, hedgerows and parks, typically anywhere with trees.
Both crepuscular and diurnal, often active from before dawn until after dusk. The activity period varies seasonally, from a full day in autumn to as little as an hour a day in winter. Grey squirrels are predominantly arboreal, but will frequently travel between trees or forage at ground level.
Nests (dreys) are constructed from hardwood twigs and leaves, and lined by dry leaves and grass, sited along branches or, in residential settings, attached to buildings. An animal may use multiple dreys as resting sites, as well as temporary tree holes gnawed in trunks
Diet: Omnivorous. Best-known for eating and hoarding acorns, grey squirrels will eat and cache other seeds, nuts and pinecones. Other dietary items include fruits, leaves, roots and flowers. They will prey on bird eggs and may also take insects.
Territoriality: Individual home ranges may cover 10 ha in some habitats; there is therefore considerable territorial overlap as squirrels occur at high densities. Animals mark territory with urine and tail-waving displays. Individuals may issue 'chuck-chuck-chuck' warning calls, sometimes towards human passers-by. Juveniles usually disperse less than a kilometre from the mother's territory.
Breeding behaviour: Male grey squirrels may travel over 100 ha during courtship. Only females exhibit parental care, carrying young on their back until independent at 10-16 weeks.
Reproductive biology: Litter size 1-8, typically 3, with potentially up to two litters (spring and summer/autumn) a year. Females will usually produce a spring litter only following good beechmast crops. The gestation period is 42-45 days.
Life cycle: Animals reach sexual maturity in 10 months to a year, and exceptionally can live to 9 years in the wild (up to 20 in captivity). Average life expectancy for animals that survive to leave the natal drey is 2 years.
The grey squirrel has been a highly successful coloniser in Britain following its introduction early in the 20th Century, its expansion facilitated by the loss of coniferous woodland that is more suitable habitat for Scuirus vulgaris. A superior competitor in broadleaved woodland and modified habitats, the grey squirrel is largely responsible for the almost complete extinction of the red squirrel on the British mainland. The species also appears to act as a carrier for Parapoxvirus, which is lethal to S. vulgaris.
In Italy, the squirrel has expanded its range from Piedmont to the Alps in the 60 years since 1948, raising concerns in the European Union that it may threaten red squirrel populations on the mainland.
Within the United States, the expansion of the eastern gray squirrel's range into the Pacific region is associated with the loss of the American red squirrel (Tamiascuirus hudsonicus) from this area.
MacDonald, D. and Barrett, P. 1993 Collins Field Guide: Mammals of Britain and Europe. HarperCollins, London. 311pp
Eastern Gray Squirrel, Wikipedia