March of the pine martens

The theory that pine martens prey selectively on grey squirrels and that this can lead to native red squirrels recolonising areas that they had been banished from by the greys is fairly well known.

It’s being investigated by researchers from NUI Galway, led by Dr Emma Sheehy, and there’s some preliminary evidence to support it.

Before about 1970 pine martens were extremely rare animals in this country, being largely confined to a few small pockets in the west, though with one significant population surviving in the Slieve Bloom Mountains in the Midlands. Their remarkable expansion since then appears to be because they got legal protection in 1970 and human persecution reduced dramatically.

Their impact on squirrel populations is not easy to prove conclusively. But I live in north Kildare and for many years I have been keeping an eye on the mammal species around here and what I’ve observed seems to provide some anecdotal support for the theory.

It’s at least 20 years since I last saw a red squirrel in the area. Since then there has been a massive increase in grey squirrel numbers. They invaded my garden and killed a sycamore tree by stripping off its bark —- sycamores are members of the maple family, cousins of the North American sugar maple, and have sweet sap which grey squirrels, another North American species, have a taste for. Then, about five years ago, all the grey squirrels suddenly disappeared. I quizzed a neighbour of mine who owns a patch of mature deciduous woodland and had been plagued by grey squirrels. His had disappeared.

At around the same time there were reports that pine martens had reappeared in the area for the first time in living memory. Much of the information that amateur naturalists get about wild mammal populations is based on identifying road kills and the first evidence of pine martens came from squashed corpses. But my friend with the wood actually spotted live pine martens hunting squirrels and rabbits on two occasions.

This pattern of events convinced me that at least part of the theory is correct. Pine martens reduce grey squirrel numbers, or even possibly eradicate them, when they move into an area. But the theory also postulates that red squirrels then move back into the territory that’s been cleared of greys.

I’ve just had a reliable report of a single red squirrel visiting a bird feeder down the road and it’s the third such sighting, in three different areas, in 12 months.