Modelling the expansion of Sciurus carolinensis (Grey Squirrels) in Lombardy, northern Italy: implications for squirrel control

1) A population of the North American grey squirrel (Sciurus carolinensis), has recently been discovered in the Ticino Park, Lombardy (N. Italy). 2) We extended Spatially Explicit Population Dynamics Models, successfully used to predict the spread of grey squirrels in England and Italy, to examine the effects of different control scenarios on grey squirrel expansion in a 20,000 km2 area around the Ticino Park. 3) Model scenarios were based on the assumption that hair-tube surveys carried out in the past reflect the actual grey squirrel distribution, which may not be accurate, and underestimate the real distribution range and current population size. 4) Simulations of grey squirrel spread indicate that, without control, grey squirrels will invade Switzerland within the next two decades, and that size and distribution of local populations of native red squirrels will be reduced. 5) Simulation of three different control scenarios suggested that efficient control, removing the alien species, is possible. 6) The main factor influencing control efficiency is the spatial distribution and total woodland size of the trapping areas. 7) Immediate actions must be undertaken, as delay in grey squirrel control will result in a population increase, undermining a successful containment programme. 8) A combination of hair-tube monitoring and a public participation survey to detect grey squirrel presence is recommended, as well as local co-operation between Italian and Swiss authorities involved in wildlife management