Even nature's fiercest rivals can sometimes live in harmony. Researchers have found a small corner of Scotland where red and gray squirrels, usually irreconcilable, are getting along splendidly.
Since the gray squirrel (Sciurus carolinensis) was introduced from North America in 1876, it has driven out the native red squirrel (Sciurus vulgaris) from most of England and Wales. The number of grays has risen to over 2.5 million, while reds have dwindled from a few million to 160,000, three-quarters of which are in Scotland. Reds die in the winter or fail to breed because they are deprived of food by grays, which can eat a wider range of seeds. Grays find it easier to digest acorns, and can eat hazelnuts earlier in the season than reds.But researchers from two government agencies, the Forestry Commission and Scottish Natural Heritage, have found stable populations of reds and grays living together in Craigvinean Forest, near Dunkeld in Perthshire.
Using radio collars to track the animals' movements within an 80-hectare section of the forest, they have been able to prove that the two species share the same habitat.
Simon Hodge, head of woodland ecology at the Forestry Commission, says that reds favor the Norway spruce and Scots pine trees on the hillsides, while grays prefer the beech and Douglas firs down by the River Tay. But both make nests, known as dreys, in each other's territory and use the same feeding grounds - and seem to have been doing so for the past 20 years.
Hodge suspects that a poor supply of beech mast may limit the number of grays, while a good supply of seeds from Norway spruces may benefit the reds. Norway spruces produce cones almost every year at Craigvinean, compared to every three or four years elsewhere, and reds find it easier to eat their small seeds than do grays. Hodge argues that understanding why squirrels cohabit at Craigvinean could help schemes to conserve reds throughout Britain.