Invasive Alien Species in Northern Ireland

Sciurus carolinensis, Grey Squirrel

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Sciurus carolinensis
© Tom Ennis
Sciurus carolinensis
© Tom Ennis
Sciurus carolinensis
© Tom Ennis
Sciurus carolinensis
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Sciurus carolinensis Gmelin 1788
The grey squirrel is a native of the deciduous forests of North America. In the late 1800s and early 1900s it was considered to be a decorative addition to the native fauna and many were released at various sites throughout Britain. A handful of grey squirrels were released in Ireland at Castle Forbes, County Longford in 1911 and have since colonised much of Ireland in less than 100 years.
Typical squirrel shape with short front legs and unmistakable long bushy tail, similar to the red squirrel, but larger and sturdier. The grey squirrel does not have obvious ear tufts unlike the red squirrel, whose long ear tufts are very noticeable in winter.
Not all grey squirrels are grey; many have chestnut markings on the face, paws and hips and can be confused with red squirrels especially in summer. Winter fur is thick and silvery-grey often with a chestnut brown streak along the middle of the back. Belly fur is always white.
Country of origin
North America.
Current distribution
The grey squirrel is well established in England, Scotland, Wales and Ireland. It is also present in Northern Italy.
Location in Ireland
Grey squirrels are widespread in all counties in Northern Ireland except County Antrim. In the Republic of Ireland they are widespread in central and eastern areas.
Grey squirrels were introduced into Ireland in 1911. Six pairs were released at Castle Forbes, County Longford in the Republic of Ireland. The animals thrived and quickly spread to the surrounding counties. By 1946 grey squirrels were present in County Fermanagh in Northern Ireland. The River Shannon in the west of Ireland and the River Bann in Northern Ireland have both slowed the grey squirrel’s spread but it has recently overcome both these natural barriers and is likely to continue its colonization of the entire island.
Life cycle
If there is plenty of food available, female grey squirrels can produce two litters of young per year, one in early spring, the other in midsummer. There are usually three babies (kittens) in each litter. The mother builds a nest (drey) in which to give birth. The kittens are blind and hairless at birth and cared for only by their mother.
Grey squirrels are active during the day and spend a lot of time on the ground searching for food especially in winter. Red squirrels are rarely seen on the ground. Less timid than red squirrels, grey squirrels are often seen in parks and gardens, scavenging in bins and raiding bird feeders.
Squirrels do not hibernate but will remain in their winter nests for up to two days during very cold weather.
Wildlife and habitat impacts
The introduction of the grey squirrel to the British Isles has had a devastating effect on the native red squirrel population which has declined rapidly over the last fifty years.
Grey squirrels are particularly well adapted to life in deciduous woodland and outcompete red squirrels for available food. Often within fifteen years of grey squirrels arriving in this type of habitat, the red squirrel population has disappeared.
Red squirrels seem to be able to compete more successfully with grey squirrels in coniferous woodland and the two species can coexist if an area of woodland is large enough. Red squirrels can survive in some areas if they are given extra food. The food must be placed in special feeders that grey squirrels cannot use.
Red squirrels are susceptible to a potentially fatal viral disease – Parapox virus. This can be carried and spread by grey squirrels who appear to be immune to the disease.
Grey squirrels strip bark from trees so they can feed on the soft inner layers. This can cause considerable damage and in severe cases the tree may die.
Human impacts
Bark stripping can cause extensive damage to commercial timber plantations.
Key vectors
Grey squirrels were intentionally introduced into Ireland in 1911. People at this time considered the grey squirrel to be an attractive addition to the native wildlife.
What you can do as an individual
Report grey squirrel sightings to CEDaR, Botany Department, Sciences Division, National Museums Northern Ireland, 153 Bangor Road, Cultra, Holywood, County Down BT18 0EU. Tel: 028 9039 5256, email[at]
Management measures
Habitat management can be used to discourage or encourage grey squirrels into specific woodland areas.
Cage trapping can be used to control grey squirrels in certain areas. Sustainable Forestry Operations Grants are available for the control of grey squirrels. For more information contact Forest Service, Tel: 028 9052 4466.
Management groups
A Northern Ireland Squirrel Forum (NISF) has been established to bring together statutory and non-statutory organisations as well as representatives of country parks and local volunteer organisations dedicated to protecting the red squirrel in Northern Ireland.
The NISF produced the Red Squirrel Action Plan (1999-2004) which was published by the EHS. A new 10-year Action Plan is proposed for the future.
At present the forum is in discussion with the Republic of Ireland to develop an all-Ireland Red Squirrel Action Plan.
Further information
UK Strategy for Red Squirrel Conservation - Action Plan for N. Ireland
Invasive Species in Ireland
Northern Ireland Forest Service
Forest Research - Management of grey squirrels
European Squirrel Initiative
Recent changes in the distribution of red squirrels in Northern Ireland
Proceedings of the Irish Red Squirrel Conservation Symposium
Northern Ireland's Mammals, Amphibians & Reptiles
Hayden, T. and Harrington, R. (2000). Exploring Irish Mammals. Town House and Country House Ltd., Dublin.
See the Invasive Species Ireland web site for further information -
Text written by:
Angela Ross, Curator of Vertebrates, Ulster Museum