Translocated native pine martens Martes martes alter short-term space use by invasive non-native grey squirrels Sciurus carolinensis.
Predators can shape the distributions and dynamics of their prey through direct and indirect mechanisms. Where prey animals are regarded as pests, the augmentation of predator populations might offer a potential tool in their management. Declines in invasive non-native grey squirrel Sciurus carolinensis populations in Ireland and Scotland have been related to an increase in range and density of native pine marten Martes martes populations. These reductions in grey squirrel abundance have, in turn, been linked to recovery of native red squirrels Sciurus vulgaris. Taking the opportunity presented by a conservation translocation of pine martens from Scotland to Wales, we investigated the short-term effects of exposure to translocated martens on the space use and survival of resident grey squirrels. Grey squirrel range size and daily distance travelled increased significantly with increasing exposure to martens but we found no effect of marten exposure on the recapture probability (i.e. apparent survival) of the sampled squirrels within the study time frame. This is suggestive of contemporary, non-lethal effects changing the ranging or foraging regimes of squirrels, due either to predator avoidance and/or earlier lethal effects associated with a reduction in intraspecific competition. Synthesis and applications. Our evaluation mimics the conditions experienced by grey squirrels at the front edge of naturally recovering pine marten populations and presents direct evidence that pine marten translocations could play an influential role in the behaviour and dynamics of invasive non-native grey squirrel populations. Translocations of native predators, undertaken primarily for biodiversity conservation, could therefore find additional application in managing the ecological and economic impacts of invasive non-native prey.