Pine Martens Can Be Used to Control Invasive Grey Squirrels


For many years, populations of the red squirrel, a native of Europe, have been in serious decline because of competition for food from an invasive North American grey squirrel. The grey squirrels also carry diseases for which the native animal has no defence. But, there is hope for the little red guy with the cute ear tufts.

New research suggests that native pine martens are suppressing the invading squirrels’ numbers. This means that if we can protect the pine marten, we have every chance of protecting the red squirrel.

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Red squirrel: what a heartbreaker

Here in Ireland the red squirrel’s numbers are declining faster than ever. So it makes sense that a team of researchers from the Waterford Institute of Technology got together with Christopher Sutherland of the University of Massachusetts Amherst, and Xavier Lambin and Emma Sheehy of the University of Aberdeen, Scotland to work out what can be done.

They chose to do their research in Scotland, and it is here that they discovered the pine marten is the best thing to happen to the native red squirrel populations.

Sheehy says, “Our study has confirmed that exposure to pine martens has a strong negative effect on grey squirrel populations, whereas the opposite effect was observed in red squirrel populations who actually benefitted from exposure to martens.”

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Grey Squirrels: the bad guys.

Sutherland adds, “Our state-of-the-art analysis suggests that we can achieve conservation objectives twice over by allowing a native species, the pine marten, to spread naturally while conserving our precious red squirrel. There has been a vigorous effort to eradicate the grey squirrel at the same time pine martens had retreated north, but the evidence is, that is changing. Pine martens are now turning up in areas where they used to be and are suppressing grey squirrel populations just through the natural order. They keep the invasive squirrel in check, if not in decline, and we are seeing a recolonisation of the red squirrel. We’ve potentially found an answer that doesn’t require the high cost of eradication.”

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Grey squirrels: bad asses

In their paper, named “The enemy of my enemy is my friend,” the authors point out that most studies of this kind “mostly consider the impact of a single enemy, despite species being embedded in complex networks of interactions.” By contrast, they modelled not only the two squirrel species “linked by resource and disease-mediated apparent competition,” but also a second enemy-mediated relationship, with the native marten.

Sutherland, an expert in ecological and population modelling, says the researchers deployed feeders in the field that had sticky tabs to capture hair samples of both squirrel species and pine martens. Using DNA from the hair samples, they were able to identify individual pine martens in each study area and map where they were spending most of their time.

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The pine marten: here to save us all!

“Pine martens provide an ecosystem service by suppressing invasive grey squirrel populations. This is good news for both red squirrel conservation efforts and the timber growing industry, due to the detrimental impact of the invasive grey squirrel on both.”

The current study, which took place between 2014 and 2017, built on evidence from a 2014 investigation by Sheehy which suggested that pine martens may be responsible for the decline of grey squirrels in Ireland.

So there you have it folks, the enemy of your enemy can sometimes be your friend.


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