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Grey squirrels are mainly grey on both body and tail, but some areas of fur may be more gingery-brown. The underside of the body is white. They constantly twitch their long tails, which are abundantly fringed with long, straight, black-and-white-tipped hairs. Black morphs occur in some parts of the range.
The highly invasive grey squirrel is abundant and familiar almost everywhere in England and Wales and is still expanding its range in Scotland.
Grey squirrels occur in all woodland, but are most abundant in mature deciduous woods; they also occur in open habitats (e.g. gardens, farmland) where trees are present. They readily cross open areas without trees, but hesitate to cross open water.
|Native range:||North-Central U.S.A., Northeastern U.S.A., Southeastern U.S.A.|
|Status in England:||Non-Native|
|Status in Scotland:||Non-Native|
|Status in Wales:||Non-Native|
|Location of first record:||Llandisilio Hall|
|Date of first record:||1828|
This species is native to the eastern part of North America, from Texas and Florida northwards to Saskatchewan and southwestern Quebec and is also called the eastern grey squirrel. There is also a western grey squirrel S. griseus, native to the western USA.
The first recorded occurrence in GB was at Llantysilio Hall in Denbighshire in October 1828. In 1938 it was declared illegal to import grey squirrels into GB or keep them in captivity, but by this time the species was well established and spreading rapidly in many parts of GB.
There were multiple introductions and naturalisation attempts made in GB between 1876 and 1929. These were highly successful. On several occasions populations originated from the release of fewer than ten individuals.
Constantly expanding in GB, Ireland and in Italy. Introduced in three different localities of northern Italy from 1948 to 1994, it is established in a large portion of Piedmont, along the Ticino valley and in an urban park in Genoa. It is expected to colonise France and Switzerland in the next few decades and may eventually invade a large portion of Eurasia. Density is usually below 3 individualsha (spring density in England 2.4–2.7), but higher in optimal habitats (18 ind.ha in an urban park in Italy; 3–18 ind.ha in an oak forest in GB).
Dispersal is facilitated by (but not dependent on) wooded corridors. Mean rate of colonisation in GB is 18 km2yr and in Italy 17.2 km2yr, ranging from 1.1 to 250 km2yr depending on habitat quality and connectivity.
Most females begin to reproduce at around 15 months old and usually bear two litters per year (December–February and May–June), each of 2–4 (up to 8) young. Gestation lasts 44 days.
In the native range they are preyed upon by mink, weasels, red foxes, bobcats, wolves, lynxes and several birds of prey. In GB red foxes, sparrowhawks and tawny owls occasionally prey on grey squirrels.
Grey squirrels occupy all kinds of landscape, provided there are tall trees. Mature, well-sheltered woodlands hold high densities, whether coniferous or broad-leaved. Gardens and farmland copses and hedgerows are also occupied, where there are tall trees.
The GB and Italian distributions are still expanding. Grey squirrels have also been introduced in many localities in North America and South Africa, and to Australia (where it is now extinct).
In overlap areas, grey squirrel causes the extinction of the native red squirrel Sciurus vulgaris through competitive exclusion. Moreover, host poxvirus, fatal to red squirrels but benign to grey squirrels, dramatically increases the rate of replacement. Also cause damage to woodland through bark-stripping. Potential impact on nesting birds.
Squirrel pox virus is potentially transmissible to humans.
Severe damage to trees by bark stripping, that exposes the timber to fungal and insect attack, disrupts the flow of nutrients up the tree, and weakens the stem. They cause local damage to fruit orchards and nut trees. Many householders aiming to feed birds are thwarted or caused extra expense by squirrels eating bird food or destroying feeders.
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