Headcount 2010: the multiplication of the grey squirrel populations introduced in Italy.

The introduction of non-native animal species is an important cause of loss of biodiversity, for this reason their population control has received a lot of attention in the scientific literature. While the number of introduced species of many taxa is constantly growing, the eradication of new populations (“a posteriori” action) and the regulation of the trade of live animals and plants (“a priori” strategies) is proceeding slowly. Tree squirrels as a taxon and grey squirrels (Sciurus carolinensis) in particular are among the most successful invasive alien species. Here we present the current situation (October 2010) of the grey squirrel in Italy. The grey squirrel was first reported in Piedmont in an area around the Stupinigi forests in 1948. Subsequent major introductions were reported in Genova-Nervi (1966) and the Ticino Valley Regional Park in Lombardy (1999). In 2010, there were 24 areas with a (meta) population or nucleus of grey squirrels: 23 of these were in the three regions most affected by the invasive species Piedmont, Lombardy and Liguria. The number of known areas with grey squirrel presence has strongly increased in the last years. With the exception of the Genova-Nervi population, there is a lack of detailed knowledge on grey squirrel distribution and population size in areas where animals are now known or believed to be present. We underline the necessity to introduce immediately a ban on grey squirrel trade and, preferably, to all invasive species of the Sciuridae family, and to start immediate control or eradication actions.