Emma Cockburn

A review of the paper:

Spread and attempted eradication of the grey squirrel (Sciurus carolinensis) in Italy, and consequences for the red squirrel (Sciurus vulgaris) in Eurasia.

Bertolino, S. and Genovesi, P. (2003)

Biological Conservation 109 pp 351-358.

 

 

 

The red squirrel (Sciurus vulgaris) is a native European species. Another species, the grey squirrel (Sciurus carolinensis) is native to North America, but has been introduced to parts of Europe. This has put the two species in direct competition with each other, as both occupy the same ecological niche, sharing the same habitat, the same food sources, and being active during the same time of day. Squirrels are diurnal animals, residing in woodland areas and have a diet consisting mainly of tree seeds (Wauters et al., 2001).  

 

 

                        

 

Fig 1: Grey squirrel (Sciurus carolinensis) and red squirrel (Sciurus vulgaris)

From: www.forestry.gov.uk

 

 

In Britain and Ireland introduction of the American grey squirrel in the 19^th century has led to a serious reduction of the red squirrel population. Grey squirrels have colonised 90% of England and Wales (www.europeansquirrelinitiative.org), and red squirrels in Britain are now confined to areas in the North of Scotland, and Northwest England and Wales (Gurnell and Pepper, 1993).Grey squirrels are not susceptible to the squirrelpox virus that affects red squirrels, but they are carriers of the disease, which is fatal (www.forestry.gov). The grey squirrel population is not only a threat to red squirrels, but also has a detrimental affect on the habitat in which they reside. Grey squirrels cause damage to trees due to their bark-stripping behaviour, which exposes the trees to attack by fungi and insects (fig 2).

   

 

Fig 2: Grey squirrel damage to hornbeam and oak in England.

From: www.forestry.gov.uk

 

 

The red squirrel is considered to be a threatened species in Europe, and introduction of the grey squirrel into Italy could potentially be disastrous for the red squirrel in continental Europe. In the British Isles the sea prevents further spread of grey squirrels onto the continent, but from Italy there are several routes through which the population could reach other countries (fig 3).

 

 

 

Fig 3: Potential Expansion corridors from northern Italy, showing habitat, and the current grey squirrel range.

From: Bertolino & Genovesi, 2003.

 

 

This paper discussed the attempted eradication of the grey squirrel after its introduction to northern Italy in 1948, and again in 1966.

The grey squirrel population in northern Italy has shown similar exponential growth patterns to that in Britain, and consequently national and international organisations drew attention to the potential spread of these animals, and the urgency with which the problem needed to be dealt with. It would be easier to eradicate the population while it was still confined to small areas. The Bern convention on conservation of European wildlife and Natural habitats requires that each contracting party “strictly control the introduction of non-native species” (www.defra.gov.uk), so the National Wildlife Institute (NWI), with the University of Turin, proposed a three-stage action plan.

This consisted of           a) monitoring of the grey squirrels’ range,

b) a trial eradication, and

c) eradication of the entire Piedmont population.

 

The trial eradication programme was to take place in an area of 170 ha, which was isolated from other populations by roads. The plan was sent to the main non-government organisations, including animal rights groups, for approval; and following this a ‘Panel of euthanasia’ plan was adopted as the most humane method. This plan was approved by government and non-government organisations and went into action in 1997. Trapping and euthanasia of the squirrels was effective in minimising stress to the animals, and in two trapping sessions over half of the population had been captured, with no accidental capture of other species.

 

The coordinator of the trial eradication and the director of the NWI were taken to court one month later by three animal rights groups, on charges of illegal hunting, damage to state property and cruelty to animals. This forced the programme to a halt while the case was on trial, which lasted for two and a half years. The directors were found guilty of illegal hunting and cruelty to animals.

 

During this time the population of grey squirrels grew considerably, reaching the edge of the Alps, the hilly areas around Turin, and the Eastern edge of Piedmont. Eradication of this species is no longer feasible, as the time, resources and skills required to do so are too great. The population has also spread to areas in which an eradication programme would require complicated authorisation procedures from numerous organisations. The authors believe this would still be an option, but only with full government action and commitment, and substantial resources.

 

It is predicted that the grey squirrel could reach France in 30-50 years, and could colonise the entire red squirrel geographical range in the medium-long term.

 

The authors, working for the NWI, have presented a scheme to the Ministry of Environment for control of further expansion of the grey squirrel population, and protection of the red squirrel population. This scheme has been approved and will involve definition of key areas of conservation, local eradication in potential expansion corridors and re-introduction of the red squirrel into areas where it has disappeared (after removal of grey squirrels).

 

This paper highlights the difficulties of dealing with invasion by alien species, and the importance of fast action. The grey squirrels could potentially have been eradicated, but will now spread to the rest of the continent over the coming decades, posing a serious threat to the native red squirrel and its habitat.

 

 

References:

 

Bertolino, S. and Genovesi, P. (2003). Spread and attempted eradication of the grey squirrel (Sciurus carolinensis) in Italy, and consequences for the red squirrel (Sciurus vulgaris) in Eurasia. Biological Conservation 109 pp 351-358.

 

Gurnell, J. & Pepper, H. 1993. A critical look at conserving the British red squirrel Sciurus vulgaris. Mammal Review, 23, 127–137.

 

Wauters, L.A., Gurnell, J., Martinoli, A. & Tosi, G. 2001. Does interspecific competition with introduced grey squirrels affect foraging and food choice of Eurasian red squirrels?

Animal Behaviour, 61, 1079–1091

 

http://www.defra.gov.uk/wildlife-countryside/resprog/findings/non-native/ecoscope-sect4.pdf

 

http://www.forestry.gov.uk/forestry/infd-6l6c36

 

http://www.forestry.gov.uk/forestry/infd-6l4f7q

 

http://www.europeansquirrelinitiative.org/news_update.html