Consequently, a new approach is needed to provide effective control of the grey squirrel in European landscapes, reducing their economic cost (> £10 million per annum in Britain alone, Mayle and Broome 2013) and reversing their replacement of the native red squirrel. At present, culling is the only means available to control grey squirrels as efforts to develop an immuno-contraceptive for grey squirrels continue with no practical and deliverable method yet available (Barr et al. Cost and effort required impedes successful control both locally and nationally in Great Britain and Ireland (Manchester and Bullock 2001), whilst in Italy, objections by animal rights groups have hindered control efforts (Genovesi and Bertolini 2001 Lioy et al. However, success has been localised and arguably ineffective, with few successful outcomes (Schuchert et al. Ĭontrol of the grey squirrel has been attempted in Britain and Ireland via culling to mitigate their impacts. In order to prevent a repeat of this situation in Italy and continental Europe, efforts are required to manage or eradicate grey squirrels. However, the most important factor remains grey squirrels acting as a vector for squirrel pox virus (SQPV) causing mortality in red, but not grey squirrels (Tompkins et al. 2019) in red squirrels during co-occurrence may also play a role.

Recent research suggests that alterations to microparasite communities (Romeo et al. Replacement of red by grey squirrels is due to factors including: larger individual mass and greater population densities of grey squirrels decreases in red squirrel fecundity, residency and recruitment (Wauters and Gurnell 1999 Gurnell et al. 2010), particularly the red squirrel which has been replaced across much of its former range in Britain (Lloyd 1968).

The species negatively impacts forestry (Mayle and Broome 2013) and native biodiversity (Hewson and Fuller 2003 Newson et al. Introduced from North America to Great Britain and Ireland in the nineteeth and twentieth centuries (Lloyd 1968), it is now in Italy where its presence poses a risk to the rest of continental Europe (Bertolino et al. One IAS of widespread concern in Europe is the eastern grey squirrel ( Sciurus carolinensis). the development of resistance or predation on non-target species (Hays and Conant 2007 O’Donnell et al. The introduction of disease or predators from the native range of an IAS (Simberloff and Stiling 1996 Shine 2010) may lead to unintended negative consequences, e.g. 1992) or a pathogen (Cooke and Fenner 2002). 2007) or biocontrol via the introduction of a predator (Lindquist et al. Mitigation of these losses can take the form of direct culling (e.g. 2009), a cost that has likely increased due to continued increases of many IAS. The annual economic cost of IAS to Europe in 2009 was estimated at €12 billion p. Awareness, and the ability to measure impacts, of IAS on economies, health and ecosystem services is increasingly being recognised and documented (Charles and Dukes 2008 Kelly et al. Impacts by IAS on native biodiversity, to which IAS are a global threat (ISAC 2006), have been widely reported. Invasive alien species (IAS) arise when non-native species become established in a new environment and negatively impact the naive ecosystem. Our review provides evidence for the mechanism driving the current decline in grey squirrels in Ireland and Scotland and supports the hypothesis that in the presence of a shared predator, direct predation influences the outcome of species interactions between native red and non-native grey squirrels. Predation of grey squirrels was significantly higher than red squirrels and was recorded only in spring and summer. Both squirrel species occurred in the scats of pine marten confirming its role as a predator of these species. We review the literature and reanalyse a new dataset to provide further data on the occurrence of both squirrel species in the scats of pine marten.

It is hypothesised that direct predation, facilitated by a lack of behavioural response, is the mechanism driving this relationship. The mechanism whereby this effect occurs remains unclear. However, exposure to pine martens ( Martes martes) has been demonstrated to reverse the competitive outcome between red and grey squirrels. In parts of Europe, introduced eastern grey squirrels ( Sciurus carolinensis) have caused regional extinctions of the native red squirrel ( Sciurus vulgaris).

Invasive alien species pose one of the greatest threats to global biodiversity.

Squirrel predators