Taxonomic name: Sciurus carolinensis Gmelin 1788
Common names: Grauhoernchen (German), gray squirrel (English), grey squirrel (English), scoiattolo grigio (Italian)
Organism type: mammal
The grey squirrel (Sciurus carolinensis) is native to deciduous forests in the USA and has been introduced to the UK, Ireland, Italy and South Africa. In the introduced range grey squirrels damage trees by eating the bark and in Europe they cause the local extinction of red squirrel (Sciurus vulgaris) populations through competition and disease.
The grey squirrel (Sciurus carolinensis) is a medium-sized tree squirrel with no sexual dimorphism in size or colouration. Ranges of external measurements (in mm) are: total length, 380-525; length of tail, 150-250; length of hind foot, 54-76; length of ear, 25-33. Adult body mass ranges from 300 to 710g. The back is grizzled dark to pale grey and may be washed with cinnamon on hips, feet, and head. Ears are buff to grey to white in the north; tail is white to pale grey. Underparts are white to grey to buff to cinnamon. In the native range of the species in North America melanism is common in the north and albinism is rare (Koprowski, 1994).
agricultural areas, natural forests, planted forests, ruderal/disturbed, scrub/shrublands, urban areas
Grey squirrels (Sciurus carolinensis) survive best in mature deciduous woodland where there is a mixture of nut producing species that produce food that can be stored overwinter. In the UK they are common visitors to urban gardens where they frequently eat food left out for birds.
In overlap areas, the grey squirrel (Sciurus carolinensis) causes the extinction of the red squirrel (see Sciurus vulgaris in IUCN Red List of Threatened Species) through competitive exclusion. It can also cause damages to woodland through bark stripping activity, sycamore (Acer pseudoplantanus) and beech (Fagus sylvatica) are particularly badly affected (Bertolino and Genovesi, 2003). Grey squirrels also act as a reservoir for a poxvirus that red squirrels are affected by. This has been postulated as another reason why red squirrels go extinct in the presence of grey squirrels; a phenomonon known as pathogen-mediated competition (Gurnell et al. 2006). Squirrels can be a garden pest by digging up bulbs and eating the bark of ornamental plants.
Grey squirrels (Sciurus carolinensis) are harvested for food in Mississippi (USA). Squirrels are popular animals to watch throughout their native and introduced ranges.
Grey squirrels (Sciurus carolinensis) cache food in small pits to see them through the winter. They have excellent spatial memory allowing these caches to be relocated.
Native range: Grey squirrels (Sciurus carolinensis) are found in the eastern United States (U.S.); the range extends west to the edge of the deciduous forest and north to Canada.
Known introduced range: Introductions occurred in California, Montana, Oregon, and Washington in the U.S., and Quebec, New Brunswick, British Columbia, Manitoba, Nova Scotia, Ontario and Saskatchewan in Canada. Eastern gray squirrels were introduced to Italy and England from the U.S., to Scotland from Canada and to South Africa and Ireland from England. An introduction from England to Australia in the 1880s failed by 1973 (Koprowski, 1994).
Introduction pathways to new locations
Local dispersal methods
Natural dispersal (local):
The Forestry Commission, in the United Kingdom, have a research programme that includes investigating the impact of grey squirrels on woodland biodiversity & identifying efficient control strategies, developing cost effective methods of managing impacts on timber production, developing a decision-support system for woodland managers on targeting grey squirrel control to support sustainable forest management, and promoting and supporting best practice management for the control of grey squirrels and their impacts. Please follow this link for an annual summary of their research
Physical: Physical management of grey squirrels includes bounty payments, free cartridges (for shooting), tail bonuses, and trapping.
Chemical: Warfarin (anti-coagulant) is the only cost-effective method of control currently available.
Grey squirrels (Sciurus carolinensis) eat nuts, buds, flowers, seeds, fruits, fungi, some insects and occasionally bird eggs. During low food periods, they strip bark to get to inner bast and cambian layers. They also feed on maize if grown close to woodlands.
Placental, sexual. 2-3 young per litter, 1-2 litters per year.
This species has been nominated as among 100 of the "World's Worst" invaders
Compiled by: IUCN/SSC Invasive Species Specialist Group (ISSG)
Last Modified: Monday, 17 October 2005