Pine Martens Saving Red Squirrels: Solution to Invasive Grey Squirrels?

It may seem odd that pine marten which are a predator of red squirrels can actually help save them from the ravages of grey squirrels, but that is the case.

Can Pine Martens help solve the problem of invasive Grey Squirrels?

Grey Squirrels are an invasive species introduced from North America. Mostly they are currently a problem in UK, Italy and Ireland. However there are concerns that the ones in Italy, “where they mostly exist in discrete, but slowly expanding, populations” (*1), will spread into the rest of Europe.

“Italian grey squirrels are edging closer to the northern border and are perilously close to crossing the Alps.”
– Dr Lisa Signorile, Department of Life Sciences , Imperial College London

Grey squirrels present a number of problems; They outcompete for food with the native red squirrels (Grey squirrels are twice as heavy as red ones) they spread the squirrel pox virus (parapoxvirus). The grey squirrels themselves are immune to squirrel pox, but they act as carriers and transmit it to the red squirrels. As squirrel pox is fatal to red squirrels, this is one of the causes of their decline.

Since grey squirrels tend to strip bark from the branches and trunks of trees, to feed on the nutritious sap underneath, this can damage or kill the tree. In milder cases the bark stripping can result in heavy scarring which can then provides an entry point pests and diseases into the tree. This can cause problems to forest plantations which may have taken hundreds of year to become established.

“The worry is that as grey squirrel populations spread, such as if they spread from one area of Italy to another, they will tend to interbreed. Research has shown that where they interbreed, between genetically distinct populations. they develop a greater ability to spread even further.” (*4)

However, it could be that help is at hand – from Pine Martens. It has been found that, “European pine martens predate on non-native grey squirrels significantly more than native red squirrels, according to new research by Queen’s University Belfast.” (*2)

It may seem odd that pine marten which are a predator of red squirrels can actually help save them from the ravages of grey squirrels, but that is the case. Apparently both types of squirrel species are a feature of the Pine Martens diet, “but grey squirrels are preyed upon exclusively during the squirrel’s spring and summer breeding season.” (*2)

Researchers from Queen’s University Belfast set out to uncover, “why the recovery of pine marten populations in the UK and Ireland positively affect red squirrel populations, while grey squirrel numbers decline.” (*3) and what they discovered is that grey squirrels are not wary around in areas where there is pine marten scent; whereas red squirrels are much more wary.

“Red squirrels demonstrated clear behavioural responses when encountering the scent [of pine marten], visiting the feeding sites less often and becoming more vigilant, while grey squirrels did not change their behaviour, resulting in them being much more vulnerable to predation from pine martens.’ (*3)

It seems, therefore that since red squirrels have inhabited the same areas as pine marten for a long time they have learned to be wary; whereas red squirrels are oblivious to which the pine marten scent implies – ie they might get eaten.

It could also be that since grey squirrels are twice the size of red squirrels the pine marten gets a bigger meal for its efforts in hunting. An advantage that a red squirrel’s smaller size and weight gives it is that it can escape pine marten’s along much smaller and thinner branches than a grey squirrel. The grey squirrels has less options for escape.

In any event, it does seem to be the case that assisting in the growth of an existing pine marten populations, or introducing them to an area, can help help to reduce the grey squirrel population there.

Within the Scotland where red squirrels have managed to survive with less threat from grey squirrels than the rest of the UK, their position is not as safe as it ought to be. There are already twice as many grey squirrels as red squirrels in Scotland.

“There are approximately 120,000 red squirrels in Scotland, which is half the number of grey squirrels.” (*5)

(A point to note is that if you are feeding wildlife and the feeder is visited by both red squirrels and grey squirrels you can help reduce the spread of squirrelpox and other infections by ensuring wildlife feeding equipment is regularly disinfected.)

link to video plant 500 trees per hour using a rewilding stickIn order to help pine martens to survive and spread they need the restoration of forests; they need real forests with a variety of trees and other plant species; not just a mono-culture of a single species, or a few species, of trees. Like many threatened species, both pine marten and red squirrels needed greater biodiversity by creating a greater variety of habitat.

One way we contribute to the increase of habitat for pine marten, red squirrels and other species is by using a Rewilding Stick. A Rewilding Stick lets us plant seeds, such as tree seeds, directly into rough ground, out in the wild. In this way we can help forests, and their under-story, to recover far quicker than they would otherwise. The natural restoration and natural maintenance of forests is currently hampered by the lack of animal species, which would otherwise do the job. By rewilding, using a Rewilding Stick, we mimic the actions of the missing animals until such times as they can re-inhabit the area and recover their numbers. How to Make a Rewilding Stick and How to Use a Rewilding Stick.

– William Fergus Martin, Founder, Global Rewilding Initiative


[1.] Protecting mainland Europe from an invasion of grey squirrels

[2.] Pine martens predate on grey squirrels more than red squirrels

[3.] Pine martens help to restore red squirrel population in UK and Ireland, finds research

[4.] Do founder size, genetic diversity and structure influence rates of expansion of North American grey squirrels in Europe?

[5.] Scottish Squirrels: Saving Scotland’s Red Squirrels