Learning from the past to guide the future of large carnivore rewilding efforts

As apex predators, large carnivores play crucial roles in ecosystems – however their numbers have plummeted over recent decades. Relocating large carnivores can support their conservation, reintroducing a species to an area where it has been exterminated or reinforcing an existing population to increase its viability. But to date, there has been little information about what influences whether these (often costly) efforts are successful or not.

A lynx wearing a radio-tracking collar peers out of a soft-release enclosure

A collared lynx is ready to take its first step from its soft-release (acclimation) enclosure in Slovenia.

Image: Miha Krofel

An international team led by researchers at the Department of Biology analysed almost 300 animal relocations from the last 15 years, spanning 22 countries, five continents, and 18 different carnivore species, including bears, hyaenas, big cats, and wild dogs.

Overall, two thirds of relocations were successful (individuals survive over six months), with success increasing significantly since before 2007. For wild-born carnivores, success rates increased from 53% to 70%; and for captive-born animals, success rates doubled from 32% to 64%.

Using a ‘soft release’ increased the odds of success 2.5-fold; this involves acclimatising the animal to the new environment before it is fully released. Releasing wild-born and younger animals (particularly 1-2 years old), also increased success rates. The latter may be because younger animals have greater behavioural plasticity to adapt to new environments, and they are less likely to have developed homing behaviours.

However, just over a third of the relocated animals were observed to find a mate and/or raise a cub in their new habitat. This demonstrates the ongoing challenges to establishing new populations and, crucially, the importance of protecting those that already exist.

Lead author Seth Thomas remarked:

In the last 15 years we have become more successful at translocating and reintroducing large carnivores. This allows us to be optimistic for the future of rebuilding damaged ecosystems around the globe, but we must remember that it is always more important to protect large carnivore populations where they are now before we lose them. Even as we have grown to be more successful, 34% of individual translocations fail and they can not be seen as a replacement for immediate conservation action to save these populations.

In the near future, relocating large carnivores may become increasingly necessary as habitats become altered due to climate change, and if land use changes increase conflict between humans and animals. In the UK, one of the most nature-deprived countries in the world, there have been calls to reintroduce formerly native apex predators, such as wolves and the Eurasian lynx.

Professor David Macdonald, a co-author for the study, said:

As the UN decade of ecosystem restoration gets underway, successful relocations of large carnivores have the potential to make a substantial contribution to biodiversity conservation. Our study provides the most geographically comprehensive sample of relocated large carnivores to date, thereby providing the evidence that conservationists and policy makers need to improve rewilding efforts.

Professor Alastair Driver, the Director of the charity Rewilding Britain (who were not directly involved in the study) said:

This study could not come at a better time here in the UK, with the devolved governments at last consulting positively on the merits of species reintroductions and various groups working hard on the feasibility of reintroducing species such as the European Wildcat and Eurasian Lynx. We still have a long way to go to overcome the misconceptions which dominate societal concerns around sharing our human-dominated landscape with other apex predators, but this report and the successes which it documents, will be hugely valuable in securing a more "grown-up" discussion on the subject. 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.

To read more about this research, published in Biological Conservation, visit: https://doi.org/10.1016/j.biocon.2023.109909