If this article is correct the latest weapon in the fight against the non native grey squirrel could be the pine marten. It seems that pine martens help to drive out the grey squirrel leaving the red squirrels to increase in numbers. In areas where there is a strong population of pine martens there now appears to less grey squirrels. The pine martens appear to eat a large number of the grey squirrels whilst the red squirrel is more agile and less likely to feed on the ground making it harder to catch.
Pine martens were almost extinct in the UK but have been reintroduced in some areas, increasing in Scotland and Ireland. Although they are still rare in England and Wales research shows they could be useful in controlling the grey squirrels numbers. Perhaps its time to introduce a few more pine martens as a natural means of culling squirrels.