New study identifies key success factors for large carnivore rewilding efforts

 

• The findings are based on data from almost 300 relocations of large carnivores, from wolves to bears;
• Relocations showed a high overall success rate, and a significant increase over recent years;
• Key factors that boosted survival of relocated animals included using younger animals, using wild-born animals, and including an acclimatisation period;
• Low mating success of relocated animals indicates ongoing challenges for rewilding programmes.

New research published today has identified the top factors that determine whether efforts to relocate large carnivores to different areas are successful or not. The findings could support global rewilding efforts, from lynx reintroductions in the UK to efforts to restore logged tropical forests.

 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, for instance to reintroduce a species to an area where it has been exterminated, or to reinforce an existing population to increase its viability. But to date, there has been little information about what factors determine whether these (often costly) efforts are successful or not.

The study was carried out by an international team led by researchers at the University of Oxford’s Department of Biology, Wildlife Conservation Research Unit (WildCRU), and School of Geography and the Environment. The group analysed data from almost 300 animal relocations which took place between 2007 and 2021. These spanned 22 countries in five continents, and involved 18 different carnivore species, including bears, hyaenas, big cats, and wild dogs.

Key findings:

• Overall, two thirds (66%) of the relocations were successful (where the animal survived in the wild for over 6 months).
• Success rates for large carnivore relocations have increased significantly since before 2007. For wild-born carnivores, success rates increased from 53% pre-2007 to 70%; and for captive-born animals, success rates doubled from 32% in pre-2007 to 64%.
• The species with the highest success rates included maned wolves, pumas, and ocelots which had a 100% success rate. The species with the lowest success rates (around 50%) were African lions, brown hyenas, cheetahs, Iberian lynx, and wolves.
• Overall, using a ‘soft release’ increased the odds of success by 2.5-fold. This involves acclimatising the animal to the new environment before it is fully released.
• Releasing younger animals (particularly 1 -2 year olds), also increased success rates. This may be because younger animals have greater behavioural plasticity to adapt to new environments, and they are less likely to have developed homing behaviours.
• For animals born in captivity, the success rate decreased by 1.5-fold, compared with animals born in the wild.
• However, just over a third (37%) of the relocated animals were observed to find a mate and/or raise a cub in their new habitat.

Although the fact that most relocated animals survived is encouraging, the authors say that the low mating success shows the ongoing challenges facing rewilding efforts and, crucially, the importance of protecting habitats that already exist.

Lead author Seth Thomas (Department of Biology, University of Oxford) 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 cannot 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 (WildCRU, Department of Biology, University of Oxford), a co-author for the study, said: ‘As the UN decade of ecosystem restoration gets underway, the ecological need and political appetite for relocations of large carnivores has never been greater, and they have the potential to contribute more now than ever before to biodiversity conservation. By scrutinising the most geographically comprehensive sample of relocated large carnivores to date, our study makes plain to conservationists and policy makers the urgency of improving 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.’

Dr. Miha Krofel (University of Ljubljana), a co-author who worked on lynx reintroductions included in the study said: ‘The main reason that allowed us to quantify the higher rate of success is the wider applicability of tracking technology compared to 15 years ago. Nowadays, many practitioners and scientists fit animals with tracking tags for better post-release monitoring of the translocated individuals. This allows us to learn from past releases to improve our interventions in the future.’

Caribou have been using same Arctic calving grounds for 3,000 years

 

IMAGE: ALASKA'S BARREN-GROUND CARIBOU HAVE BEEN USING THE SAME PARTS OF THE ARCTIC NATIONAL WILDLIFE REFUGE TO GIVE BIRTH TO THEIR CALVES FOR AT LEAST 3,000 YEARS, ACCORDING TO RESEARCHERS. view more 

CREDIT: MICHAEL MILLER

Caribou have been using the same Arctic calving grounds for more than 3,000 years, according to a new study by the University of Cincinnati.

Female caribou shed their antlers within days of giving birth, leaving behind a record of their annual travels across Alaska and Canada’s Yukon that persists on the cold tundra for hundreds or even thousands of years. Researchers recovered antlers that have sat undisturbed on the arctic tundra since the Bronze Age.

“To walk around the landscape and pick up something that’s 3,000 years old is truly amazing,” said Joshua Miller, an assistant professor of geosciences at the University of Cincinnati.

He has been leading summer expeditions to the Arctic National Wildlife Refuge since 2010, using rafts to navigate remote rivers to search for caribou antlers exposed on the tundra.

“We think about having to dig down into the soil to find that kind of ecological history, but on the Coastal Plain, the vegetation grows extremely slowly,” Miller said. “Bones dropped by animals that lived dozens or even hundreds of generations in the past can provide really meaningful information.”

The study demonstrates how important the area is for an animal that native Alaskans and Candians still depend on for sustenance, even as energy companies seek to exploit oil and gas resources in this protected area.

The Biden Administration in 2021 suspended drilling leases in the Arctic National Wildlife Refuge, the largest tract of undeveloped wilderness in the United States. 

“We know this region of the Arctic National Wildlife Refuge has been an important area for caribou for millennia,” Miller said. “That should give us pause on how we think about those landscapes.”

The study was published in the journal Frontiers in Ecology and Evolution.

Barren ground caribou undertake nature’s longest overland migration, traveling as far as 800 miles each year to reach their spring calving grounds in the Arctic National Wildlife Refuge and Canada’s Ivvavik National Park. The largest herd in this area, named for the Porcupine River, numbers in the hundreds of thousands of animals.

Scientists think caribou use these areas because they have fewer predators and offer seasonal vegetation near places where they can avoid the worst of the mosquitoes.

“The mosquitoes are horrible,” Miller said. “You get swarmed — literally covered in them. They can do significant damage to a young calf.”

Whatever the reason, the antlers they leave behind provide a physical record of their epic yearly travels that researchers can unlock through isotopic analysis. 

Caribou antlers, like those of elk, deer and moose, are made of fast-growing bone that the animals shed each year and regrow the following year.

“It is amazing to think that the oldest of the antlers found in our study were growing approximately the same time Homer was penning ‘the Iliad’ and ‘the Odyssey,’” study co-author Patrick Druckenmiller said.

He is director of the University of Alaska Museum and professor of the Department of Geology and Geophysics at the University of Alaska Fairbanks. Eric Wald from the U.S. Fish and Wildlife Service also co-authored the study.

The antler surveys in the vast expanse of the Arctic refuge require meticulous logistical planning, Miller said. Small planes deposit researchers and their gear deep in the interior, where they have to be watchful for grizzly and polar bears. They pilot rafts to the Beaufort Sea, conducting a  grid search of suitable caribou habitat identified in advance using aerial photography.

“We search for antlers along old river terraces, walking back and forth, covering every inch of habitat to find those ancient treasures,” Miller said. 

While male caribou antlers span four feet and weigh more than 20 pounds, female caribou antlers are much smaller. The antlers contain nutrients such as phosphorus and calcium that are important to plants and animals.

The dropped antlers create “nutrient sinks,” which could have a profound effect on the area’s vegetation. Miller said the caribou’s migration serves as a nutrient “conveyor belt” that might even draw caribou back to reap the benefits of this fertilizer in a reinforcement loop.

Caribou and other mammals are known to chew on dropped antlers for their valuable minerals. This could be an important dietary supplement for new caribou moms.

“We’d like to know to what degree this conveyor belt influences why caribou are going there in the first place,” Miller said.
The study was supported by the U.S. Fish and Wildlife Service, the National Geographic Society, the National Science Foundation, the Wildlife Society and the UC Office of Research.

Miller said the Arctic is warming faster than other parts of the globe. Parts of the Arctic that were once barren tundra are sprouting new spruce forests.

“We were in Arctic Village this summer, just south of the calving grounds, talking to elders about the changes they have seen,” Miller said. “Where once it was open tundra, large stretches of this barren ground are now full of trees everywhere. What will happen to the barren ground caribou as this habitat gets converted into forest?”

---

JOURNAL

Frontiers in Ecology and Evolution

DOI

10.3389/fevo.2022.1059456