The European pine marten, Martes martes, is a member of the family Mustelidae within the order Carnivora. It is widespread throughout much of north and western Europe but rare or absent in much of its historic southern European range. The pine marten is omnivorous and feeds upon a wide variety of food including small mammals, birds, reptiles and amphibians, invertebrates, fruit, nuts and carrion in various proportions throughout the seasons, however diet is usually dominated by just two or three food categories, depending on seasonal and regional food availability. The pine marten is closely associated with forests and has traditionally been considered a forest specialist, however despite their close association with trees, they are not strictly forest-dependent and have adapted to a variety of landscapes throughout their range, not least in Ireland and Britain where deforestation in the 19th century led to <5 % forest cover.
Pine martens (Martes martes) are the second rarest mammal in Britain, and although they are recovering well in Scotland and Ireland (a result of increased habitat availability and legal protection), they remain practically extinct in England and Wales; a result of habitat loss, and historic persecution. The Vincent Wildlife Trust is currently undertaking a population reinforcement project in Wales.
The Shropshire Wildlife Trust are supporting what may be the only breeding population of pine marten in England.
Pine Martens confirmed as key to reversing grey squirrel invasion
A study published today (Wednesday, March 7, 2018) has shown that pine martens can help in the conservation of red squirrels – by reversing the spread of invasive grey squirrel populations.
Scientists from the University of Aberdeen, Waterford Institute of Technology and the University of Massachusetts Amherst have published their study ‘The enemy of my enemy is my friend: native pine marten recovery reverses the decline of the red squirrel by suppressing grey squirrel populations’, in the journal Proceedings of The Royal Society – B.
The study, which was led by Dr Emma Sheehy and Professor Xavier Lambin from the University of Aberdeen’s School of Biological Sciences, used DNA forensics and state of the art analyses to test the hypothesis that pine martens are suppressing grey squirrel populations in Scotland.
The research took place in the Scottish Borders – an area which pine martens have recently begun to recolonise, Central Scotland – where there is a more established pine marten population – and in the Highlands, where there are no grey squirrels but a long established pine marten population coexists with native red squirrels.
223 multi-species feeders were deployed throughout the three regions, baited with a mixture of nuts and seeds. Sticky patches placed under the lid collected hair samples from squirrels and pine martens that took the bait. Trail cameras were also used to improve detectability of red squirrels in particular, who often didn’t leave hair behind as pine martens had saturated the sticky patches with their hair before red squirrels got there.
The study built on evidence from a 2014 study, which suggested that pine martens may be responsible for the decline of grey squirrels in Ireland, and confirms that the relationship between red and grey squirrels in the UK is clearly altered in the presence of a native predator.
Dr Chris Sutherland of the University of Massachusetts Amherst explains: “Studying wildlife can be difficult, particularly when investigating multi-species relationships. As such our study offers what is a very rare insight into the potential role of native predators in shifting dynamics between native and invasive prey species.
With the hair samples collected, DNA forensics were used to identify individual pine martens and spatial statistical models were then used to reconstruct individual pine marten home ranges. From this we were able to quantify how much red and grey squirrels were exposed to these pine martens, and most importantly, how this is affecting their distribution”.
“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”, says Dr Sheehy.
“Our occupancy modelling offered further insight into the possible mechanism at play. There are two steps to occupancy models, first determining the factors which affect the probability of detecting a species, given they are present, and second the probability that the focal species actually occupy the site. The detection component of our models showed that where pine marten activity was high, red squirrels took longer to use the feeders, which suggests red squirrels modify their behaviour to be more cautious when their natural predator is around.
“This type of behaviour is to be expected from species that have co-evolved together On the other hand, no such caution was identified in the grey squirrel population, which suggests they may be easier prey to find, and much more susceptible to predation by pine martens. This is a really interesting result, and contradicts the “landscape of fear” theory which suggests grey squirrels are avoiding pine martens rather than being heavily preyed upon. However, further research is needed in order to define the exact mechanisms taking place.”
“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. The pine marten is already heavily suppressing grey squirrel populations where they are well established, and presumably this influence will spread as the pine marten’s range expands southwards through Scotland and into the North of England but this is likely to be a slow and very gradual process.”
The study took place between 2014 and 2017 and was funded by the Irish Research Council and the EC under the FP7 programme, and Forestry Commission Scotland.
Further information and quotes
Professor Xavier Lambin from the University of Aberdeencommented: “The findings are good news for red squirrel conservationists, as the study confirms that the benefits to red squirrel populations that arise from the reduction in grey squirrel abundance far exceed the impact of any predation by pine martens on some red squirrel individuals, hence the title we gave to the study -The enemy of my enemy is my friend”, says Professor Lambin. “Even where pine martens reach the highest density in the Highlands, where grey squirrels are absent, there is no hint of any negative association between pine marten density and red squirrel occupancy”.
Dr Emma Sheehy said: “Globally, there are numerous examples of non-native predators having detrimental impacts on native prey, such as the fox and domestic cat which continue to wipe out native marsupials in Australia. In our study, we demonstrate a similar scenario, only in this case it is a recovering native predator having a detrimental impact on an invasive prey, which colonised the region while the native predator was absent. Clearly with the recovery of the native predator, the advantage has shifted in favour of the native prey species. It is really encouraging news both locally and in a global context, as it supports the concept that ecosystems with native predators can offer greater resistance to invasive species”.
Kenny Kortland, Species Ecologist with Forest Enterprise Scotlandsaid “The findings of this research are extremely encouraging. It seems we have a very welcome ally in our efforts to protect red squirrel populations on the national forest estate. The research demonstrates that the return of native predators can have beneficial impacts for other native species.’’
Emma Stewart, an Environment Forester with FESwho recently witnessed at first hand a pine marten predating a grey squirrel in North Lanarkshire said “I couldn’t believe my eyes when I watched a pine marten carrying a grey squirrel into the tree canopy and then eat it. To be lucky enough to see this beautiful creature return to this area is amazing and I hope more people have the chance to experience wonderful wildlife moments like this in our forests and woodlands”.
Dr Emma Sheehy said: “The pine marten is a slow-breeding species however, which lives at naturally low densities compared to similar sized predators such as the American mink. Historically they were widespread throughout the UK but deforestation and persecution in the 19thand 20thcenturies led to their virtual extinction in England and Wales, with a remnant population holding on in the North of Scotland. They have been protected by law since the 1980’s and have gradually started to recolonise Scotland, benefitting also from an increase in forestry”.
A spokesperson from Forestry Commission Scotland added“We welcome the findings from this research and the promise of a natural predator to help regulate grey squirrel numbers. It is exciting to know that our native pine marten can help with the recovery of our native red squirrels and their return to many parts of Scotland. The natural expansion of pine martens through Scotland’s forests once again demonstrates the high biodiversity value of these woodland habitats.”
Dr Sheehy said: Due to the damage grey squirrels cause in the UK by bark stripping tree species such as oak, beech and sycamore, the findings are of great interest to foresters both economically and in terms of forest biodiversity.
Jonathan Spencer MBE, Forest Planning and Environment Manager with Forest Enterprise and Forestry Commission England said: “The new insights emerging from this elegant study are very welcome indeed. The damage inflicted by grey squirrels on native trees is considerable, and runs into millions of pounds worth of damage each year. If a landscape supporting pine martens reduces the numbers of grey squirrels to the point where that damage is absent or significantly removed, the future for forestry based on native and other vulnerable timber tree species is far more assured”
Dr Mel Tonkin, Project Manager of the Saving Scotland’s Red Squirrel project, said “We are very excited to finally have some research which clearly shows that the recovery of the pine marten, a protected native predator, is having clear benefits for native red squirrels in Scotland, just as Emma Sheehy and her team found in Ireland”.
“Saving Scotland’s Red Squirrels is a partnership project, led by the Scottish Wildlife Trust, to protect Scotland’s red squirrels from replacement by the introduced American grey squirrel. With the support of landowners and local volunteers we are carrying out strategic, landscape-scale control of grey squirrel populations in areas where it will bring the greatest benefit to Scotland’s red squirrels”.
“It is a considerable challenge for us to sustain this work over the long-term, which is required if we are to prevent the ultimate demise of our much-loved red squirrels. This new research gives us hope that at some point in the future, the pine marten will take over some of this grey squirrel control for us. However, it is important that people understand that it may take several decades for pine martens to recover to densities that will allow us to put away our traps altogether. If we stop the work we are doing now, there won’t be red squirrels left for the pine martens to save”, says Dr Tonkin.
Adrian Vass, spokesperson for the Red Squirrel Survival Trustsays “We welcome this first step on the evidential road in this vital area so relevant to our native red squirrels and native broadleaf trees. This research coincides with the development of an oral contraceptive and delivery system to prevent grey squirrels from breeding, an innovation that offers the potential for grey squirrel management in areas without predatory species.”
“Pine martens are recolonising their historic range through the south of Scotland and into the north of England but “this is likely to be a slow and very gradual process” says Dr Sheehy. “We’re not going to see any dramatic changes in distribution overnight, but all in all, things are certainly looking up for pine martens, red squirrels and native biodiversity”.
See also October 2018 article in the News section of this website.