Native and invasive squirrels show different behavioural responses to scent of a shared native predator

Invasive species pose a serious threat to native species. In Europe,
invasive grey squirrels (Sciurus carolinensis) have replaced native red
squirrels (Sciurus vulgaris) in locations across Britain, Ireland and
Italy. The European pine marten (Martes martes) can reverse the
replacement of red squirrels by grey squirrels, but the underlying
mechanism of how pine martens suppress grey squirrels is little
understood. Research suggests the reversal process is driven by direct
predation, but why the native red squirrel may be less susceptible than
the invasive grey squirrel to predation by a commonly shared native
predator, is unknown. A behavioural difference may exist with the native
sciurid being more effective at avoiding predation by the pine marten with
which they have a shared evolutionary history. In mammals, olfactory cues
are used by prey species to avoid predators. To test whether anti-predator
responses differ between the native red squirrel and the invasive grey
squirrel, we exposed both species to scent cues of a shared native
predator and quantified the responses of the two squirrel species. Red
squirrels responded to pine marten scent by avoiding the feeder,
increasing their vigilance, and decreasing their feeding activity. In
contrast, grey squirrels did not show any anti predator behaviours in
response to the scent of pine marten. Thus, differences in behavioural
responses to a shared native predator may assist in explaining differing
outcomes of species interactions between native and invasive prey species
depending on the presence, abundance and exposure to native predators.