Are pine martens and red squirrels teaming up to prey on grey squirrels?

PEOPLE out and about during the October bank holiday, especially in wooded areas, may see some native red squirrels as autumn is a busy time for them. They can be observed feasting on nuts, seeds and berries and gathering their hoards of food for winter months ahead.

We’ve seen these delightful creatures with the trademark bushy tail a number of times in recent weeks on the ground and on trees. During the splendid weather, everyone seemed to be talking about the beauty of trees in their varied seasonal hues of brown, orange, bronze and gold, enhanced by squirrels and other wildlife.

The Irish red squirrel has some serious survival issues to contend with, but it has been spared the scourge of leprosy which has hit the population in Scotland and England.

In Ireland and the UK, the American grey squirrel threatens the survival of the reds for two reasons — competition for food and disease from greys, which are carriers of the fatal squirrel pox but immune to it themselves. Other predators include foxes, cats, dogs, and the pine marten. However, most conservationists agree, the biggest danger comes from invasive grey squirrels, which are almost twice the size of the reds. Zoologist Emma Sheehy has found the pine marten, itself a threatened species, may be helping the reds by preying on the greys.

Writing in Ecologist magazine, she says the impact in Ireland has been particularly notable. Her four-year study found pine marten recovery in the Midlands was linked to such a significant decline in grey squirrel numbers that the once-beleaguered red squirrel population was able to take back its former range, including woodlands which had been dominated by greys for more than 30 years.

Dr Sheehy’s study provided the first evidence for what foresters and gamekeepers had been saying for years — where pine martens had returned to healthy numbers, grey squirrels had all but disappeared. In areas with few or no pine martens, greys persisted.

Red squirrels, on the other hand, have coexisted with pine martens throughout much of Europe for tens of thousands of years. The two species evolved together. While pine martens will very occasionally eat red squirrels, they don’t seem to have a negative impact on population numbers, Dr Sheehy believes. In the Irish study, the areas reds had recolonised were exclusively those with healthy pine marten populations. Red squirrels are doing well only in parts of Ireland including Laois, Offaly and north Tipperary.

Greys are thriving in other areas, including much of the east, and a study by Emily Goldstein, in UCC, has confirmed the grey squirrel is expanding into the south west.