A recent study by biologists at the University of Aberdeen suggests that pine martens, the natural predator of red squirrels, are unexpectedly helping out red squirrels
To answer why, we first need to talk about squirrels. When Europeans came back from their visits to the Americas, they often brought back unusual animals. These animals were usually sold to the wealthy. Estate owners wanted grey squirrels for there own back gardens (albeit, very big back gardens).
But this is where the problems began.
These small populations within the isolated estates began to spread. The grey squirrel started to out-compete the native red squirrel; they grow faster, bigger, and reproduce more often.
Grey squirrels were also carriers for squirrel-pox, a virus they have immunity against. The red squirrels were not immune, with the spread of the virus contributing greatly to the red squirrels decline.
Today, there are 250 grey squirrels for every red squirrel in the UK.
The pine marten is the natural predator of squirrels in the UK. The members of the weasel family have struggled with fur hunting in the past, but changes to the law, alongside conservation efforts means that a pine marten comeback has begun.
The study, has discovered that grey squirrels are more heavily effected by pine marten presence than red squirrels. The authors of the paper suggest that red squirrel behaviour has evolved during times when pine martens were common. The reemergence of pine martens has made grey squirrels more vulnerable to predation than red squirrels. As grey squirrels have not been historically exposed to pine martens, evolution of avoidance behaviours hasn’t been favoured
Although red squirrels still die, dwindling grey squirrel populations at sites where pine martens are present provides an opportunity for red squirrels to thrive.
So the red squirrels predator, the pine marten, seems to be doing them a favour