Paula White, a wildlife biologist, was examining lion skulls to estimate the animals’ ages when she noticed something odd about their teeth. Rather than just showing the normal, gradual wear that occurs over time, a sharp, V-shaped notch was cut into the back edge of the canine teeth of some big cats.
The bizarre markings, it turned out, were caused by snares — circular thread traps that wrap around an animal’s neck or leg like a noose. Traps are typically a death trap, but the lions whose skulls Dr. White was investigating apparently managed to escape by pulling the wire with their teeth.
Putting this together “was a real a-ha moment,” said Dr. White, a researcher at the University of California, Los Angeles. “It was a bit chilling, but fascinating at the same time.”
dr. White and her colleague, Blaire Van Valkenburgh, a vertebrate paleobiologist also at UCLA, realized they had come across a valuable data set — one that allowed them to calculate the frequency of non-fatal human-caused injuries to large carnivores.
Their findings, published Thursday in the journal Frontiers in Conservation Science, were worse than expected. More than a third of the lions and a fifth of the leopards they examined showed signs of entanglement at some point in their lives. More than a quarter of the lions also had lead shotgun bullets in their skulls, indicating a previous encounter with poachers or other humans.
“If we want these big cats to thrive, we need better data on the nature and magnitude of the threats they face, especially from humans,” said Dr. Van Valkenburgh. “We can get that data by documenting the history of insults in their bones and teeth.”
African lions are rapidly declining. Between 1993 and 2014, the population declined by 43 percent, to just 23,000 feral individuals remaining today. Less extensive evidence indicates that leopard numbers are also declining.
Habitat loss is the main threat to lions and leopards, but humans also pose a significant threat to the big cats from poaching. While the illegal international trade in lions and other felines is on the rise, some big cats are currently being killed in retaliation for predators. Others are killed by snares set up for animals such as gazelles and antelopes that are part of the bushmeat trade. The snares harm the survival of the big cats by incapacitating the prey they depend on for food, and incidentally capturing and killing the predators.
However, it is challenging to determine the full magnitude of the impact of entanglement and conflict with people. Animals are often killed in very remote locations and cases go unreported. “Usually, animals just disappear and you don’t know what happened to them,” said Dr. white. When conservationists do manage to collect data, it usually relates to deaths rather than injuries.
The researchers aren’t sure how the injuries they’ve documented could affect lions and leopards, but they suspect it must be significant.
“You’re looking at an animal that relies on its ability to hunt and take down large prey, which is not an easy way to live,” added Dr. White to it. “Any kind of physical injury will make his life more difficult.”
The new study — probably the first to systematically document such injuries — came about by chance. dr. White had originally worked with the Zambian government on a project that photographed the skulls and skins of adult male lions and leopards that had been legally hunted as trophies in Zambia’s Luangwa Valley and the greater Kafue ecosystem.
The archived photos were the starting point for the new research. While examining the skulls, Dr. white and dr. Van Valkenburgh stated that as many as 37 percent of the 112 lions and 22 percent of the 45 leopards had become entangled at some point in their lives. And 27 percent of the lions had been hit in the face with bullets.
The results are almost certainly an underestimate. For the snare calculations, the researchers only considered animals that had both tooth wear and associated scars on their skin — not those with just tooth wear. For the shotgun estimates, they could only examine images of the animals’ skulls, not their entire skeletons. Like dr. White said, “Our reported numbers are conservatively low, even if they are high.”
While the findings cannot be directly extrapolated to other lion and leopard habitats, Dr. Van Valkenburgh points out that the approach is “easily repeatable in countries without deep pockets or access to advanced technology.”
Joel Berger, a biologist at Colorado State University and the Wildlife Conservation Society, who was not involved in the study, agreed that the new method has “really broad value.”
“This is a remarkable paper that uses an imaginative diagnostic approach,” he said.
Human-caused carnivores deaths are a major problem around the world, but there are few studies that provide insight into this issue at a local level, Dr. Berger. However, that kind of detailed information is needed if conservationists are to do more than make blind guesses about how best to help carnivores survive.
According to Amy Dickman, a conservation biologist at the University of Oxford, Dr. white and dr. Van Valkenburgh “that entanglement and conflict may be even greater threats than previously believed.”
This highlights the need to prioritize finding solutions to these problems, added Dr. Dickman to it. For example, she said people would be less likely to capture animals if they had access to enough food, and less likely to retaliate against predators if they were given education and support to better protect themselves and their livestock. Getting people directly involved in conservation and making sure they get tangible benefits from living with wildlife are also part of the solution, said Dr. Dickman.
However, conservation is complex and even in the best of conditions, wildlife can still come under pressure from humans. For example, the landscapes in Zambia where the research took place are considered bastions of conservation, with strong anti-poaching programs and community involvement. The fact that snares and conflict between humans and wildlife are so high, even in these places, was a sobering revelation, said Dr. white.
“It’s hard to say ‘more effort’, because clearly there is already a lot of work to be done,” she said. “But if it doesn’t work, you need to reconsider.”
