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We are getting better at putting big predators back into wild places


We’re getting better at putting big predators back into wild places

New research shows measures such as acclimation pens and using wild-born animals helps reintroductions succeed.
February 22, 2023

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Toothy predators are celebrities of the animal kingdom. Whether it’s wolves in Montana, snow leopards in Central Asia, grizzlies in Alaska or lions in Africa, we are drawn to their displays of power, even when it comes with a tingle of fear. There’s a reason why that Disney blockbuster isn’t called “The Zebra King.”

That helps to explain why the release of such animals back into their native habitat is often accompanied by headlines and predictions that such animals will be ecological saviors or menaces. But after the animals have been set free, there is another question: Did it work?

Now, new research suggests that in recent decades, people have gotten better at successfully reintroducing these large carnivores back into their native habitats. Over roughly the last 15 years, two-thirds of these reintroduced predators have survived, a marked improvement over earlier efforts.

“We have become more successful at translocating and reintroducing large carnivores,” said Seth Thomas, an Oxford University scientist involved in the new research. “This allows us to be optimistic for the future of rebuilding damaged ecosystems around the globe.”

Such successes are important for a variety of ecological and political reasons. As apex predators at the tops of food chains, big predators can have an outsized influence on an ecosystem. The disappearance of wolves from Yellowstone National Park, for instance, helped set off a cascade of changes that led to larger elk herds, over-grazed meadows and heavily eroded stream banks. Their reintroduction in the 1990s helped reverse some of that damage.

A number of these species are severely endangered or have been erased from their historic habitat, making reintroductions a key tool. And, as charismatic creatures that capture people’s imaginations, the prospect of returning them to a place can also draw public attention to broader conservation issues such as habitat protection.

But it’s not just a matter of opening a cage and letting an animal go. Thomas teamed up with scientists from Europe, South America and South Africa to scrutinize the track record of past large carnivore reintroductions to better understand which factors played a role in success or failure.

They gathered details from projects spanning 22 countries in five continents and 18 different species. The list reads like a who’s who of the stars of nature documentaries: jaguars, ocelots, pumas and maned wolves in South America; brown bears, leopards, tigers, hyenas and snow leopards in Asia; cheetahs, lions, leopards, wild dogs and hyenas in Africa; lynx and wolves in Europe; and black bears in the U.S.


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All told, it added up to 297 individual animals between 2007 and 2021. The number doesn’t account for all the large predators released during that time, only ones where scientists could find enough data to make meaningful comparisons.

The survey showed that 66% of the animals survived past 6 months in the wild, the researchers reported Feb. 16 in Biological Conservation. That’s better than earlier results. A study of more than 2,000 such releases between 1990 and 2007 found that just 32% of captive-bred carnivores survived, while 53% of wild-sourced animals made it. By comparison, 64% of the animals reared in captivity survived in the more recent period, as did 70% of their wild brethren.

When Thomas and colleagues looked for factors that contribute to success, several things stood out. Animals born in captivity with little experience of the broader world still fared worse than their wild-born brethren. Animals that went through a process of acclimation, called a “soft release,” were 2.5 times more likely to survive than animals put directly into the wild.

Alos, to the scientists’ surprise, animals set loose in open areas were nearly 3 times more likely to survive compared with ones put into fenced reserves. While fenced habitat might seem safer, the researchers suspect that enclosed reserves have higher densities of fellow carnivores, creating more competition.

But it’s not all good news. One-third of animals, after all, didn’t make it. And just 37% of the animals showed evidence of reproductive activity, such as finding a mate or raising young.

The “study makes plain to conservationists and policy makers the urgency of improving rewilding efforts,” said David Macdonald, an Oxford professor involved in the research.

Alastair Driver, head of the United Kingdom-based charity Rewilding Britain, said the report comes at an opportune time, as UK agencies consider the prospect of reintroducing the Eurasian lynx, an animal that last roamed the Scottish Highlands around 1,300 years ago. In recent years, the animal has been returned to Switzerland, Germany and Slovenia, and their numbers are bouncing back in Scandinavia.

“This report and the successes which it documents, will be hugely valuable in securing a more ‘grown-up’ discussion on the subject (of reintroductions),” said Driver. “I have no doubt that this will, in turn, lead to well-planned and implemented carnivore reintroductions which only 10 years ago, I would have thought inconceivable in my lifetime.”

Thomas, et. al. “Evaluating the performance of conservation translocations in large carnivores across the world.”  Biological Conservation. Feb. 16, 2023.

Photo Credit: Pavel Padalko

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