In 2016, wildlife biologist Clayton Lamb was securing a GPS collar to a tranquilized grizzly bear in southeastern British Columbia when he noticed one of its paws was missing three toes. Weird, he remembers thinking, but not surprising for the rough-and-tumble animals. Then, three more grizzlies popped up sporting similarly mangled paws. Anxious to solve the mystery behind this grisly trend, Lamb and colleagues launched a yearslong investigation. Now, they’re pointing a finger at the potential culprit: baited traps meant to capture much smaller forest animals. The team’s findings could affect local fur-trapping policies or convince authorities to delay the trapping season.
“It’s an important issue and I’m really glad they’re highlighting it,” says Christopher Servheen, a conservation biologist who studies grizzly bears at the University of Montana and who wasn’t involved with the work. He notes there may be many more bears injured by these traps that researchers never find.
When Lamb and his team arrived on the scene early in their investigation, they quickly crossed off a few potential injury causes. Signs of healing in the bears’ fractured toe bones ruled out a birth defect, whereas the clean, linear fractures—as if toes had been cleaved on a carving board—eliminated the idea they had been bitten or torn off by other animals.
Lamb’s team wondered whether body-gripping traps, a bit like oversized mousetraps, could be to blame. The small traps are usually baited with beaver meat and deployed throughout the mountains of southeastern British Columbia from November through February to capture weasel-like critters called martens for their fur. A bear ordinarily would shrug off such a small trap, but these traps have become stronger in recent years, Lamb says, as trappers have aimed to meet modern humane trapping standards by killing martens instantly.
“Grizzly bears face the perfect storm of attributes that make them susceptible to this issue,” Lamb says. “They manipulate things with their paws, they are very food motivated and they stay active well into the trapping season.”
To determine whether grizzlies are inadvertently stumbling into these traps, the team fastened four traps onto trees, but rigged them to not fully shut. Monitoring the traps via remote cameras over the next 2 weeks, they noticed grizzlies visiting all four traps, tripping two of them with their front paws and noses.
Could these traps sever bears’ toes from their paws? To find out, the team next stuck paws from deceased grizzlies into several traps commonly employed in British Columbia, then examined the carnage using x-rays.
They found the traps alone weren’t enough to fracture the bones, but they could cut off circulation to the toes, Lamb explains. Eventually, the blood-deprived digits would either rot away or be gnawed off by the bears. Because the trap creates a straight-line injury across the paw, the toes appear to have been lopped off.
They then calculated the force it would take to jostle a bear’s foot free, finding the tightest traps required more than 230 kilograms of force to open. That’s more muscle than many bears can likely muster, Lamb says. Taken together, the evidence suggests grizzlies in the region are losing toes to marten traps, the researchers reported last month in the Wildlife Society Bulletin.
These injuries have consequences for the area’s human population, too. Three of the four bears with missing toes were later involved in human-bear conflicts. One was fatally shot by a rancher, another was suspected of attacking a human. The third was captured and relocated by conservation officers after causing a ruckus on a farm.
Lamb says the bears with missing toes likely represent bolder or more curious individuals. “That translates to sticking their foot in a trap, and it also goes hand in hand with checking out someone’s chicken coop or knocking over the garbage or looking through someone’s window at the pie on the counter,” Lamb says. Another possibility is that bears accidentally wander into these traps, become injured, and then are forced to take more risks because digging for dietary staples such as tubers and insects would be more difficult with a bum foot.
Servheen thinks the pain of these traps might also make the wounded bears particularly ornery. “We can’t ignore the fact that it’s a state of constant suffering,” Servheen says. “If I put a trap like that on my hand and carried it around for a week, I’d be pretty unhappy, too.”
Based on guidance from Lamb and colleagues, British Columbia wildlife officials in 2021 stipulated that all body-gripping traps deployed in November must be enclosed inside a box with an opening large enough for a marten to wriggle through, but too small to admit a bear paw. Servheen and Lamb also recommended delaying the marten trapping season until early December, after most grizzlies will have gone into hibernation, but these changes have not been implemented.
Source: Science Mag