Tooth damage in lions reveals human impact on wildlife

Populations of large predators like lions are in decline in Africa, chiefly because of the loss of suitable habitats, declines in prey populations, poaching and conflict with humans. Keeping track of the mortality rates of large predators is largely achieved by monitoring deaths through trophy hunting, but few assessments have been made of carnivore mortality or injury due to other anthropogenic causes. 

In a new study, published in Frontiers in Conservation Science, biologists Paula White and Blaire Van Valkenburgh from UCLA assess the incidence of snaring and shotgun injuries on lion and leopard populations in two wildlife areas in Zambia. The experts made use of a low-cost forensic technique involving analysis of the skulls of carnivores killed by trophy hunters in the Luangwa Valley and the Greater Kafue Ecosystem. 

While conducting research in Zambia, White noticed that some of the trophy skulls of lions had pronounced, horizontal notches on their teeth. These were not made through natural wear and tear, and White deduced they were the result of attempts by the lions to chew their way out of a snare. 

Snares are wire nooses that are illegally set by poachers to trap wild animals for food, but they are indiscriminate and carnivores can also get entangled in them. Some skulls also had lead shot pellets embedded in the bone, evidence that the lions had been in conflict situations with humans who had used shotguns to control them.

“While investigating natural age-related tooth wear and damage and naturally-occurring skull injuries for another study, we detected abnormal tooth wear that was determined to be diagnostic of wire snare damage, and old shotgun pellets embedded in skulls,” explained White, director of the Zambia Lion Project and a senior research fellow with the Center for Tropical Research at UCLA’s Institute for the Environment and Sustainability. “We realized that an individual’s history of past (non-lethal) injuries could be determined through simple forensic examination.”

“It was an odd mix of thrilling to figure out the cause of the notches and horrifying to realize that so many animals had been entangled in a share at some point in their lives,” she said.

The researchers used photographs of lion and leopard skulls to determine tooth damage from snaring and to locate embedded shotgun pellets. They looked at samples of 112 lions and 45 leopards from the two areas in Zambia.

Of these animals, 37 percent of the lions and 22 percent of the leopards had snare scars and tooth notches. This incidence was much higher than they had expected.

Evidence of shotgun pellet injuries was only found among lions, with 27 percent of sampled individuals having shotgun pellets embedded in their skulls. Double injuries from both snare damage and shotgun pellets were found in 16 percent of lions from the Kafue area and 7 percent of lions from Luangwa.

The researchers had expected to see more injuries among carnivores from the Luangwa Valley, where the human population is larger and conflicts more likely. However, these anthropogenic injuries were more prevalent among lions and leopards in the Greater Kafue area. 

“The Luangwa Valley and the Greater Kafue Ecosystem are two premier wildlife tourism areas in Zambia. Our findings indicate that even in these well-protected systems, poaching and human-wildlife conflict represent significant threats to large carnivores,” said White.

“Our procedure of forensic examination of carnivore skulls and teeth, some of which can be applied to live-captured animals, allows for improved detection of cryptic, non-lethal anthropogenic injuries,” explained the study authors.” 

“Further, our methods represent a consistent and economical way to track changes in the frequency of such injuries over time and between regions, thereby providing a direct measure of the effectiveness of conservation programs that seek to reduce poaching and human-wildlife conflict.”

“Despite the alarmingly high frequency of non-lethal injuries that we detected, we know that our findings are an underestimate,” said White. “Our methods may serve to improve future assessments of the total impacts that humans have on wildlife and provide a measure of the effectiveness of select conservation programs.”

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By Alison Bosman, Earth.com Staff Writer