The Capercaillie Conundrum

As the political and cultural tension around Scotland’s capercaillie reaches a new high, the population of the world's largest grouse hits a new low. Is it time to ditch the dogma and think outside of the box?

Scotland’s capercaillie are slowly but surely disappearing, threatening to leave our woods haunted by the loss of one more species. This isn’t the first time the world’s largest grouse has faced local extinction. In fact, the western capercaillie – to give it its proper name – was hunted to extinction in Scotland by 1785, before being reintroduced 50 years later. By 1970, around 20,000 birds roamed Scotland’s pinewoods. For a while, forest clearings reverberated once again with the vibrant pop and gurgle of displaying males, but from this high point, the population has suffered an inexorable decline. The latest survey suggests as few as 542 birds remain. What has happened?

Capercaillie haven’t been hunted in Scotland for a long time, so hunting isn’t to blame for the current crisis. This time the problem is more complicated, and much harder to fix. A recent NatureScot review identified low breeding success as the key factor preventing capercaillie recovery, believed to be due to a combination of climate change (wetter springs reduce the availability of insects just when chicks need them), disturbance (from people and their dogs), and predation. For a small, fragmented population, these combined pressures are unsupportable. The situation is dire.

And so, as news broke of the latest devastating survey results, there were renewed calls for “bold action” and “collaborative conservation”. Crucially, many believe Scotland’s capercaillie cannot be saved without tackling the predators they suspect are preventing its recovery, with at least some evidence suggesting that pine martens may have a disproportionate effect on capercaillie breeding success.

Pine marten (martes martes) leaping in woodland at dusk, Scotland.

Pine martens are also legally protected and still recovering from centuries of habitat loss and persecution.

However, to date, the RSPB and others have been reluctant to accept this narrative. They argue that predation is over-emphasised as a threat compared with the impacts of climate change and habitat management. Recent data from lek counts in Abernethy Forest also suggests that capercaillie numbers can be stabilised without removing predators, while wider experiments across the Cairngorms Connect landscape suggest diversionary feeding may reduce localized rates of nest predation, with work continuing to elucidate whether this translates into any easing of the pressures on chick survival.

In reply, critics argue that the existing Abernethy data does not provide enough evidence to peg all our hopes on. It has even been suggested that Abernethy’s spectacular Caledonian forest is such good habitat that it may be drawing in birds from surrounding areas, masking local losses. Some feel that in a world where conservation organisations such as the RSPB already kill other predators to protect threatened species, there is no reason not to cull pine martens, assuming it is the only way to save capercaillie.

Young scots pines regenerating after removing grazing pressure, Rothiemurchus Forest, Scotland.

The expansion of the pinewoods at Abernethy has been beneficial to capercaillie – and pine martens.

There is a risk of studying the problem to death, and time is a luxury we no longer have.

The uncomfortable possibility is that resurgent pine martens may now be a problem for Scotland’s last few capercaillie, but nobody knows for sure, nor can anyone say whether removing them would make a real difference. On the other hand, there is a risk of studying the problem to death, and time is a luxury we no longer have.

Against this troubled backdrop, NatureScot’s recent review identified one possible solution. Alongside measures to address disturbance and expand habitat, an advisory panel recommended exploring the possibility of translocating pine martens out of core capercaillie breeding areas. The idea had obvious appeal. It avoided the unwelcome prospect of killing pine martens, it offered a potential lifeline to Scotland’s capercaillie, and it offered some potential benefits to other species.

In theory, translocated pine martens could be used to reinforce the leading edge of their recovery elsewhere, potentially accelerating natural recolonisation of the species’ historical range. That in turn might be good news for red squirrels, which are thought to benefit from the pine marten’s predation of non-native grey squirrels (the smaller, nimbler reds are seemingly less vulnerable to marten predation than their American cousins). 

Amid all the division and despair, this translocation proposal appeared to offer that rarest of things in conservation: a win-win scenario. If pine martens could be captured and removed from the few remaining areas that still support healthy numbers of capercaillie, it might – just might – afford capercaillie the breathing space they need until habitat quality can be improved and connectivity increased.

Capercaillie, Tetrao urogallus, male displaying surrounded by hens on lek at sunrise, April

Importantly, the localised removal of pine martens need only be temporary, ceasing once capercaillie numbers have recovered to a point where breeding success is no longer critically impaired by predation. And if removing pine martens failed to manifest an upward turn in capercaillie numbers, the scheme could quickly be abandoned. Trapped areas would quickly be recolonised. No harm, no foul.

Unfortunately, the speed with which trapped pine martens might be replaced is one reason that key stakeholders already consider the translocation proposal non-viable. Pine martens have been translocated before, but welfare concerns mean that trapping is limited to late summer and early autumn, when that year’s kits have reached independence, but before winter makes translocations more challenging. Trapping in the spring, which would be of most benefit to breeding capercaillie, would risk separating dependent kits from their mothers, but trapping in the autumn would leave too long a window for dispersing pine martens to backfill vacated territories.

Modelling also suggests that there may be limited sites that translocated pine martens could be moved to. Although there is a lot of unoccupied habitat still out there, relatively little of it is free from the risk of persecution or road mortality. IUCN guidelines stipulate clearly that animals should not be translocated where threats have yet to be removed or sufficiently reduced and that “justifying a conservation introduction requires an especially high level of confidence over the organisms’ performance after release.”

The capercaillie conundrum is both a symptom and a consequence of Scotland’s ecological decline.

Sadly, there is a growing feeling that capercaillie may not be saveable in Scotland. With a rise of 1.9oC above pre-industrial temperatures by the 2050s, it has been suggested that capercaillie could lose 99% of suitable habitat. We are already at 1.3oC of warming and capercaillie are declining across western Europe. They may soon therefore become restricted to the Eurasian boreal zone where, for now, they remain abundant. Of course, nobody wants to give up on Scotland’s capercaillie, but privately there is growing talk of a “managed retreat”.

More profoundly, the capercaillie finds itself at the centre of a philosophical debate, subject to the question of whether we should intervene, perhaps indefinitely, to secure the survival of individual species or whether we should, with regret, let nature take its course. When land managers call for radical interventions to save this iconic bird, and especially when such interventions include calls for the removal of native predators, rewilders tend to recoil, pointing out that so-called single-species conservation has conspicuously failed to tackle the larger systemic crises facing the natural world.

The capercaillie conundrum is both a symptom and a consequence of Scotland’s ecological decline. Many of the species that once contributed to maintaining healthy, functional living systems are now missing. Natural processes, such as predation and scavenging, are often suppressed, while the complex interactions between predators that once existed have been disturbed by local and national absences. Today, golden eagles and goshawks, which both naturally target pine martens, continue to suffer persecution across much of Scotland. With greater ambition – and greater tolerance – our pinewoods could support a wilder, more complementary mix of species, including the return of lynx. In turn, these predators could offer more ways to regulate the impact of smaller predators like foxes and pine martens on capercaillie.

Goshawk, Accipiter gentilis, female feeding on red grouse on plucking stump in forest, Scotland

Expanding populations of goshawk could help capercaillie by predating pine martens.

In Scotland’s greatly altered ecosystems, even rewilders recognise the need to interfere sometimes. If the capercaillie had not already been reintroduced, rewilders would likely be calling for its reintroduction. There are no easy answers here, no options that do not involve some compromise and loss. And yet, given time and enough global action to tackle climate change, capercaillie might still adapt to survive in Scotland. Recent evidence from Germany suggests that lekking activity (when males compete to attract females) is advancing by about half a day per year in what appears to be a response to the shifting emergence date of caterpillars – an important local food source.

View across Glenmore Forest tpwards Ryvoan Pass, Cairngorms National Park, Scotland.

Restoring the Caledonian pinewoods offers hope for the beleaguered capercaillie but this forest will take decades to fully mature.

No single measure will save Scotland’s capercaillie. In the long run, we need healthier, more complete woodland communities, functioning in better-connected landscapes, shaped and governed by natural processes. With the threat of climate change, even that might not be enough. But if we want to buy time, and if the objections can somehow be resolved, pine marten translocations might yet achieve a rare win-win, benefiting capercaillie in this moment of crisis and generating a boost for wider rewilding efforts. That seems worth the sort of bold collaborative effort that many are calling for.