Details of this species in United Kingdom (UK) Status: Alien
Invasiveness: Invasive
Occurrence: Reported
Source: Mayle, B. and Smith, L., in press Arrival Date: 1876
Introduction: Species Notes for this Location:
The grey squirrel (Sciurus carolinensis) was introduced from USA and Canada to approximately 30 sites in England and Wales and 3 sites in Scotland between 1876 and 1929. By 1945
grey squirrels were present throughout much of south east and southern England, midlands and the Welsh borders and Yorkshire. Within a period of just one
human lifetime they have completely replaced the native red squirrel through out most of England and Wales - despite strenuous efforts to control their
spread through a bounty scheme in the 1950’s (Mayle, B. and Smith, L., in press). Management Notes for this Location:
The red squirrel is a priority species under the UK Governments Biodiversity Action Plan process. The Species Action Plan (SAP) for red squirrels, formed in 1995, aimed to re-establish red squirrel populations, where appropriate, and maintain and enhance current populations through good management. Such is the threat from grey squirrels, the main focus of work has had to concentrate on identifying and protecting key sites for red squirrel conservation. The criteria used to identify key sites include extent and suitability of habitat, how easily a site can be defended, current threat from grey
squirrels and level of land owner support.
The best illustration of conservation action being taken is the work underway in the North of England to define Reserves where action on protecting the red squirrel will be directed. Priority sites for red squirrels have been identified, and a landscape level strategy and plan with full community involvement/ownership agreed. There have been considerable - and successful – attempts to raise public awareness and secure support. A review of current methods of surveillance for both squirrel species is currently taking place with the aim of producing a protocol for a national monitoring scheme that will allow us to assess regional population trends and the effects of interaction between the squirrel species. This scheme should also allow us to assess the efficacy of conservation management on local red squirrel populations. Other research priorities include; the impact of grey squirrels on woodland birds, silvicultural approaches to minimise damage, research to identify squirrel pox virus disease in the environment and modes of transmission, and fertility control to limit rates of population expansion and damage impacts. The high risk/high cast nature of the research needed for the
last two items, and the lack of available funding, is hampering progress (Mayle, B. and Smith,
L., in press).
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. Impacts:
Agricultural: Damage by grey squirrel (Sciurus carolinensis) is a major concern to the forestry industry, and the current national policy of increasing the level of broadleaf planting is
being seriously undermined (Mayle, B. and Smith, L., in press).
Competition: Grey squirrels (Sciurus carolinensis) compete for resources with with native small mammals including mice, voles and in particular, the red squirrel (see Sciurus vulgaris in IUCN Red List of Threatened Species) and common dormouse (see Muscardinus avellanarius in IUCN Red List of Threatened Species) (Mayle, B. and Smith, L., in press).
Disease transmission: The incidence of squirrel poxvirus (SQPV) in red squirrels appears to be related to the level of presence of the grey squirrels (Sciurus carolinensis) in an area, suggesting they are involved in transmission of the disease. The presence of the disease significantly increases the rate of replacement of the native red by the grey squirrel by as much as 20 fold. Greys can be infected by SQPV, but it appears to be benign (Mayle, B. and Smith, L., in press).
Habitat alteration: Grey squirrels (Sciurus carolinensis) effect woodland structure and composition and sustainable woodland/forest management through damage to tree stems and branches, by feeding on
seeds and plant bulbs (e.g. the English bluebell, Hyacinthoides nonscripta) thus preventing regeneration (Mayle, B. and Smith, L., in press).
Physical disturbance: Grey squirrels cause serious damage by stripping the bark from trees. This exposes the timber to fungal and insect attack, disrupts the flow of nutrients up
the tree, and weakens the stem (Mayle, B. and Smith, L., in press).
Predation: Grey squirrels (Sciurus carolinensis) predate the nests of a wide range of bird species both in North America and Britain. Species most at risk are those with open nests in the
canopy, although birds nesting on the ground and in the understorey are also vulnerable (Mayle, B. and Smith, L., in press). Last Modified: 17/10/2005 2:34:19 p.m.
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