Between 2019 and 2021, a team from Gloucestershire Wildlife Trust trapped thirty five wild pine martens in the Scottish Highlands and released them into the Forest of Dean, a species that had not lived in that stretch of England for well over a century. The original aim was simply to bring pine martens back for their own sake, a native predator restored to a native woodland. What happened next turned out to be more interesting, and more complicated, than anyone fully expected.
What the Martens Started Doing
Pine martens are not fussy eaters, but their diet in the Forest of Dean quickly began to include a species nobody had specifically asked them to target. Researchers monitoring the new population, checking marten droppings for evidence of what they had actually been eating, found that grey squirrels were making up around fourteen per cent of the martens’ diet within a fairly short time of their release.
That is not, on its own, an especially dramatic figure. What made it worth paying attention to was a pattern already observed in Scotland, Ireland and Wales, where earlier pine marten recoveries have coincided with grey squirrels declining in the same areas and native red squirrels, which had often been pushed out entirely, beginning to reappear. The theory, still being tested, is that red squirrels have retained some evolutionary memory of how to evade a predator they coexisted with for millennia, while grey squirrels, native to North America and only introduced to Britain a little over a century ago, simply have not had time to develop the same instincts. Where a marten moves in, the theory goes, reds hold their ground better than greys do.
Why This Matters Beyond the Squirrels
Grey squirrels are not merely an inconvenience to have around. They strip bark from oak, beech and sycamore, sometimes seriously damaging or killing the tree in the process, and they are the principal reason red squirrels have all but vanished from most of England, driven out through direct competition and a squirrel pox virus that greys carry largely without symptoms but which is usually fatal to reds. A predator that naturally suppressed grey squirrel numbers, without anyone needing to trap, cull or administer contraception to a single animal, would be an unusually elegant solution to a problem conservationists have been managing by hand for decades.
Forestry England clearly saw enough promise in the pattern to bring pine martens back deliberately, choosing the Forest of Dean partly for its mixed woodland and partly for its proximity to the recovering Welsh population, in the hope that a similar effect might follow. A further release of thirteen martens into the Lake District this year extended the same experiment into Cumbria, an area from which the species had been absent since the close of the nineteenth century.
Why the Story Isn’t Quite That Simple
Reading further into the actual research, rather than the more excitable coverage of it, complicates the picture in a way I found genuinely useful. A recent scientific review looking specifically at whether pine martens could work as a solution across England and Wales was cautious in a way headlines about a “squirrel solving predator” rarely are. It pointed out that pine martens reproduce slowly, that they have plenty of other prey available to them so grey squirrels are never their only option, and that grey squirrels persist in urban and suburban environments where a marten, a genuinely woodland dwelling animal, is unlikely to ever follow them. The researchers’ conclusion was that pine martens should not be treated as a standalone fix, but as one useful piece of a wider strategy that still needs targeted culling, fertility control and habitat management alongside it.
Even conservationists working directly on the pine marten reintroductions themselves are candid about this. One researcher leading the South Cumbria recovery project described pine martens as a vital nature based part of the solution, in the same breath as acknowledging that ongoing grey squirrel culling and the development of oral contraceptives will still be necessary. Britain’s official grey squirrel strategy does not currently include pine martens as a formal control measure at all, partly because pine martens have their own conservation needs that come first, and partly because the evidence does not yet show the effect can be relied upon at the scale the problem actually requires.
What I Find Genuinely Interesting About This
There is a temptation, with a story like this, to reach for the cleanest possible version: nature finds its own solution, predator returns, balance restored. The actual evidence resists that framing, and I think it is more interesting for resisting it. What seems to be true is narrower and more provisional: pine martens appear to shift the odds somewhat in red squirrels’ favour where the two predators and both squirrel species overlap in genuinely suitable woodland, and that shift might, over enough time and alongside other deliberate management, help red squirrels reclaim some of the ground they have lost.
Whether that adds up to a genuine long term recovery for red squirrels in England, or simply one useful thread among several that conservationists will keep pulling on together, is not yet something the evidence can settle. The Forest of Dean and Lake District populations are still being monitored, the droppings still being checked, the squirrel counts still being taken. Nobody involved seems to be claiming victory. They seem, instead, to be watching carefully to find out what is actually true.
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