Mammals of Coombe Bissett Down: grey squirrel Grey Squirrel (Sciurus carolinensis) The fox den was visited by another familiar face: a grey squirrel. Aggressive and highly territorial, this invasive squirrel has decimated the population of our native red squirrels (Sciurus vulgaris) by outcompeting them for food and spreading a disease called Parapoxvirus, which the greys are seemingly unaffected by. Since the greys introduction from America in the 1870s, the reds have almost been led to extinction in the UK but there remains strongholds in Scotland, Northumberland, Wales, Northern Ireland, and the Lake District – plus a few islands, such as Brownsea. Pine martins (Martes martes) may offer a solution to this issue as they can act as a biotic control against grey squirrels: they are skilled hunters of a variety of mammals but are too heavy to chase down the more nimble red squirrels that can run along thinner branches of tree canopies – a strong argument for the restoration of intact food chains in our countryside. Nevertheless, grey squirrels do fill a very similar ecological niche to their red cousins, and they help the development of woodlands by widely distributing nuts and seeds. Squirrels cache the seeds and fruit of deciduous trees in autumn, which they locate in the winter through a combination of memory and scent. This particular squirrel has, perhaps foolishly, chosen to cache its food in the entrance of an active fox den.