A Grizzly Mystery: Why Did Bears Miss Toes?  |  Science

A Grizzly Mystery: Why Did Bears Miss Toes? | Science

A Grizzly Mystery: Why Did Bears Miss Toes?  |  Science

In 2016, wildlife biologist Clayton Lamb attached a GPS collar to a sedated grizzly bear in southeastern British Columbia when he noticed that one of its legs was missing three toes. Weird, he recalls thinking, but not surprising for the shaggy animals. Then three more grizzly bears with similarly mutilated paws appeared. Anxious to solve the mystery behind this eerie trend, Lamb and colleagues launched a years-long investigation. Now they’re pointing the finger at the possible culprit: bait traps designed to catch much smaller woodland creatures. The team’s findings could influence local fur catching policies or convince authorities to postpone the trapping season.

“It’s an important topic and I’m really glad they’re bringing it to the fore,” said Christopher Servheen, a conservation biologist who studies grizzly bears at the University of Montana and was not involved in the work. He notes that many more bears may have been injured by these traps that researchers never find.

When Lamb and his team arrived on the scene early in their investigation, they quickly crossed out a few possible causes of injury. Signs of healing in the bears’ broken toe bones ruled out a birth defect, while the clean, linear fractures — as if the toes had been split on a cutting board — eliminated the idea that they had been bitten or torn off by other animals.

Lamb’s team wondered if body-grabbing traps, a bit like large mousetraps, could be to blame. Usually lured with beaver meat, the small traps are deployed in the mountains of southeastern British Columbia from November to February to capture weasel-like critters called martens for their fur. A bear would normally shake off such a small trap, but these traps have gotten stronger in recent years, Lamb says, as trappers have strived to meet modern humane trapping standards by killing martens immediately.

“Grizzlies face the perfect storm of attributes that predispose them to this problem,” Lamb says. “They manipulate things with their paws, they are very motivated for food and they stay active well into the trapping season.”

To determine if grizzly bears inadvertently stumble into these traps, the team attached four traps to trees, but testified them not to close completely. They observed the traps via remote cameras over the next 2 weeks and noticed grizzlies visited all four traps, tripping two of them with their front legs and noses.

Could these traps separate the bears’ toes from their paws? To find out, the team then stuck paws of deceased grizzly bears into various traps commonly used in British Columbia, then examined the carnage using X-rays.

They found that the traps alone weren’t enough to break the bones, but they could cut off circulation to the toes, Lamb explains. Eventually, the anemic digits would either rot or be gnawed by the bears. Since the fall causes a straight-line injury to the leg, the toes appear to have been severed.

An x-ray of a grizzly bear's leg in a trap
An X-ray reveals a bear’s paw with three lost toes.Cali Lewis

They then calculated the force it would take to untie a bear’s paw, and to find the tightest traps, it took more than 230 kilograms of force to open. That’s more muscle than many bears can probably muster, Lamb says. Taken together, the evidence suggests that grizzly bears in the region are losing toes to marten traps, the researchers reported last month in the Bulletin of the Wildlife Society.

These injuries also affect the human population of the area. Three of the four bears with missing toes were later involved in human-bear conflicts. One was shot dead by a rancher, another was suspected of assaulting a human. The third was captured and moved by conservation officers after causing a commotion at a farm.

Lamb says the bears with missing toes probably represent bolder or more curious individuals. “That translates to putting their foot in a trap, and it also goes hand-in-hand with checking someone’s chicken coop or knocking over the garbage or looking through someone’s window at the cake on the counter,” Lamb says. Another possibility is that bears accidentally wander into these traps, get injured and then be forced to take more risks because digging for staples like tubers and insects would be more difficult with a vagrant foot.

Servheen thinks the pain from these traps can also make the injured bears particularly nervous. “We can’t ignore 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 guidelines from Lamb and colleagues, British Columbia wildlife officials determined in 2021 that all traps deployed in November should be enclosed in a box with an opening large enough for a marten to squeeze through, but too small. to allow a bear’s paw. Servheen and Lamb also recommended postponing the marten hunting season until early December, after most grizzly bears have gone into hibernation, but these changes have not been implemented.

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