Conserving species can be a complicated affair. Take this dilemma.

After being hunted to near extinction, numbers of a native predator are recovering and eating more of an endangered prey species, whose own numbers are declining as a result. Should conservationists accept that some successes mean losing other species, or reinstate lethal control of this predator in perpetuity?

Or perhaps there is a third option that involves new means of managing species in the face of new conditions. This issue is playing out globally, as land managers grapple with predators such as wolves and lynx reclaiming their historic ranges.

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In the ancient Caledonian pine forests of Scotland there are fewer than 500 capercaillie remaining. This grouse is beset by multiple threats, not least shifts in spring weather caused by climate change that are driving its Europe-wide decline, relating to changes in when chicks are reared and available nutrition.

Additionally, and in common with other ground-nesting birds, capercaillie lose eggs and chicks to carnivores. As such, the recovery of the pine marten (a relative of weasels and otters) from its own near extinction in Scotland is contributing to the decline of capercaillie.

Internationally, little has been achieved to slow the heating of Earth's climate, and decades of dedicated conservation efforts have not arrested the decline of capercaillie. Extinction will follow unless new solutions are found.

Killing pine martens, the capercaillie's predators, might offer short-term relief, but it is socially and politically contested and scientific evidence on its effectiveness is meagre. Most importantly, it risks undermining the recovery of species conservationists have worked hard to restore. Instead, the challenge is to reduce the effects of predators, not their numbers, and encourage coexistence between species.

We have tried one such method in Scotland - with incredibly positive results.

Our idea is simple: predators have to be efficient, so when given access to a free meal, they are less likely to hunt for harder-to-find prey like capercaillie nests.

Satiated predators are less likely to kill and eat prey that is of concern to conservationists. This is called diversionary feeding: giving predators something easy to eat at critical times, such as during the time when capercaillie build their ground nests and rear chicks between April and July.

To test this idea we systematically dumped deer carrion across 600 square kilometres of the Cairngorms national park in north-eastern Scotland, during eight weeks in which capercaillie are laying and incubating eggs. This area is home to the last Scottish stronghold of capercaillie. We also made artificial nests across the same area that contained chicken eggs, to represent capercaillie eggs.

Through this landscape-scale experiment, we showed that the predation rate of pine marten on artificial nests fell from 53% to 22% with diversionary feeding. This decrease from a 50% chance of a nest being eaten by a pine marten, to 20%, is a massive increase in nest survival.

This was a strong indication that the method worked. But we were unsure whether the effect seen in artificial nests translated to real capercaillies, and the number of chicks surviving to independence.

Counting chicks in forests with dense vegetation is difficult, and land managers are increasingly reluctant to use trained dogs. Our innovation was to count capercaillie chicks using camera traps (motion-activated cameras which can take videos and photos) at dust baths, which are clear patches of ground where chicks and hens gather to preen.

We deployed camera traps across the landscape in areas with and without diversionary feeding and measured whether a female capercaillie had chicks or not, and how many she had. Chicks are fragile and many die early in life. The number of chicks in a brood declined at the same rate in the fed and unfed areas.

However, in areas where predators received diversionary feeding, 85% of the hens we detected had chicks compared to just 37% where predators were unfed. That sizeable difference mirrored the improvement seen in artificial nest survival.

Fewer nests being predated led to more hens with broods, such that by the end of the summer, we observed a staggering 130% increase in the number of chicks per hen in fed areas - 1.9 chicks per hen were seen compared to half that in unfed areas.

So, does diversionary feeding provide a non-lethal alternative to managing conservation conflict and promoting coexistence? Our work suggests it does.

Diversionary feeding is now a key element of the capercaillie emergency plan, which is the Scottish government's main programme for recovering the species. Diversionary feeding will probably be adopted across all estates with capercaillie breeding records in the Cairngorms national park by 2026.

This rapid implementation of scientific evidence is a direct result of working closely, from conception, with wildlife managers and policy makers. For capercaillie, diversionary feeding has real potential to make a difference, a glimmer of hope in their plight (some nicer weather in spring might help too).

More broadly, for conservationists, land managers, gamekeepers, farmers, researchers and anyone else involved in managing wildlife, this work is testament to the fact that, with the right evidence and a willingness to adapt, we can move beyond the binaries of killing or not killing. Instead, finding smarter ways to promote the coexistence of native predators and native prey.

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