Pine martens are helping to control invasive gray squirrels

Native red squirrel populations in Scotland are increasing after serious decline thanks to the pine marten.

Red squirrels, a species found in Great Britain, Ireland, and other parts of Europe, have been dropping in numbers due to invasive gray squirrels, which are common in North America.

The increase in invasive gray squirrels means more competition for food, and unfortunately, prompted serious population declines for native red squirrels.

However, a new study conducted by an international team of researchers found that red squirrels are recovering because pine martens have been reducing gray squirrel populations.

The pine marten had also been facing population declines, but researchers from the University of Massachusetts Amherst, the University of Aberdeen, Scotland, and the Waterford Institute of Technology, Ireland found that the martens were making a comeback.

The study was published in the journal Proceedings of the Royal Society B.

“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 benefited from exposure to martens,” said Emma Sheehy, a co-author of the study.

The researchers discovered that even though pine martens had decreased in numbers, there has been a resurgence, with pine martens showing up back in their natural habitats and suppressing gray squirrel populations.

The study took place between 2014 and 2017 and was based on previous theories that pine martens were useful at suppressing gray squirrels in Ireland.

The researchers used DNA forensics and an analysis that combined the spatial techniques measuring pine marten population numbers and the squirrels nearby.

Feeders with sticky tabs were placed in areas with squirrels and pine martens. A DNA analysis of the hair samples stuck to the tabs indicated to the researchers what animals were prominent in those areas.

What is interesting is that the pine marten is a natural enemy of both the red and gray squirrels, but the study modeled the relationship between pine martens and the two squirrel species.

The results showed that the pine marten was actually benefiting the red squirrel and that conserving both natural predators and prey can help control invasive species.

“Our evidence that, in addition to their intrinsic value, pine martens provide an ecosystem service by suppressing invasive grey squirrel populations 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,” said Sheehy.

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By Kay Vandette, Earth.com Staff Writer

Image Credit: University of Aberdeen