This predator is an unlikely ally for declining red squirrels

August 18, 2014, 1 p.m.
pine marten

Photo: Phil Johnston/MNN Flickr Group

Pine martens are a key player in saving Ireland's red squirrels

Red squirrels are native to Europe and abundant throughout most of its habitat. But in Great Britain, Ireland and Italy, numbers have fallen dramatically due to the introduction of grey squirrels from North America. There are thought to be fewer than 140,000 individuals left in the United Kingdom, and 85 percent of those are in Scotland. The grey squirrel out-competes the red squirrel in feeding, since it can digest acorns but red squirrels cannot, and also carries a disease called squirrel parapoxvirus which kills red squirrels but doesn't seem to affect grey squirrels. In many areas, the only solution to help bring back red squirrels is for humans to eradicate grey squirrels. But research has shown that perhaps the solution lies in protecting a long persecuted predator.

After years of being poisoned by gamekeepers, trapping, and habitat fragmentation, the pine marten disappeared from much of England and Ireland, and it was only still common in northwestern Scotland. However, through protections and the reforesting of some areas, pine martens have begun to spread back into some of their historical habitat. And alongside this redistribution, researchers noticed something else interesting. Where the range of pine martens overlaps with the range of grey squirrels, grey squirrel numbers drop and leave room for native red squirrels to rebound.

In a study released in January of this year on the pine marten's influence on grey squirrels in Ireland, researchers reported, "A distribution survey of the midlands was carried out which confirmed the grey squirrel population has crashed in approximately 9,000 km2 of its former range and the red squirrel is common after an absence of up to 30 years."

It is thought that because grey squirrels spend more time foraging on the ground, they're easier for a pine marten to catch than the more arboreal red squirrel, though there are other factors including how grey squirrels simply react to a predator they didn't evolve with. These include a stress-induced reduction in breeding, changing foraging habits and simply retreating from the areas where pine martens are found. Whatever the reason for the reduction in grey squirrels, it gives the red squirrel a window to recover, and they do.

"It would seem from the evidence gathered to date that the presence of an abundant tree-climbing predator may be the cause of the grey squirrels’ retraction from the midlands, and the native red squirrel’s subsequent recovery," writes researcher .

The story of pine martens and red squirrels is a great example of how the balance of predator and prey plays a key role in the health and balance of species in an entire ecosystem. It is possible that by helping to bring back the pine marten, conservationists could make big strides in battling back invasive grey squirrels and bringing back native red squirrels.

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Jaymi Heimbuch is a writer and photographer at Mother Nature Network. Follow her on Twitter, Google+, and Facebook.