Hair traps as a source of grizzly bear injuries | Science

In 2016, wildlife biologist Clayton Lamb was fitting a GPS collar to a sedated grizzly bear in southeastern British Columbia when he noticed that one of its paws was missing three toes. Strange, he remembered thinking, but not surprising for brutes. Then three more grizzlies appeared with similarly disfigured paws. Eager to solve the mystery behind this ominous trend, Lamb and colleagues began a years-long investigation. Now they’re pointing the finger at the potential culprit: baited traps designed to catch much smaller forest animals. The team’s findings could influence local fur trapping policies or persuade authorities to delay the trapping season.

“It’s an important issue, and I’m really glad it’s being highlighted,” said Christopher Servheen, a conservation biologist who studies grizzly bears at the University of Montana and who was not involved in the work. He notes that there could be many more bears injured by these traps that researchers never find.

When Lamb and his team arrived at the scene early in the investigation, they quickly ruled out several potential 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 carving board — ruled out the idea that they had been bitten or torn off by other animals.

Lamb’s team wondered if body-trapping traps, a bit like large mousetraps, could be to blame. The small traps are usually baited with beaver meat and set in the mountains of southeastern British Columbia from November to February to catch weasel-like creatures called martens for their fur. A bear would normally escape from such a small trap, but these traps have gotten stronger in recent years, Lamb says, as traps strive to meet modern humane trapping standards by killing martens instantly.

“Grizzly bears face the perfect storm of attributes that make them susceptible to this problem,” says Lamb. “They manipulate things with their paws, they are very motivated by food and they stay active during the trapping season.”

To determine whether grizzlies were inadvertently falling into these traps, the team attached four traps to the trees, but rigged them so that they did not close completely. Monitoring the traps via remote cameras over the next 2 weeks, they observed grizzlies visiting all four traps, tripping two of them with their front paws and noses.

Can these traps tear bears’ fingers from their paws? To find out, the team then stuck paws from deceased grizzlies into several traps commonly used in British Columbia, then examined the carnage with X-rays.

They found that the traps alone weren’t enough to break the bones, but they could cut off blood flow to the toes, Lamb explains. Eventually the bloodless fingers will either rot or be gnawed by the bears. As the trap creates a straight line injury through the paw, the toes appear to be severed.

An X-ray reveals a bear’s paw with three missing toes.Callie Lewis

They then calculated the force it would take to push a bear’s leg out and found that the tightest traps required more than 230 kilograms of force to open. That’s more muscle than many bears can possibly muster, Lamb says. Taken together, the evidence suggests that grizzlies in the region are losing toes to marten traps, researchers reported last month in Bulletin of the Wildlife Society.

These injuries also have consequences for the population in the area. 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 assaulting a person. The third was captured and moved by conservation officers after causing a disturbance on a farm.

Lamb says bears with missing toes probably represent bolder or more curious individuals. “It translates to putting their foot in a trap, and it also goes hand-in-hand with checking someone’s coop or knocking over the trash or looking through someone’s window at the pie on the counter,” says Lamb. Another possibility is that bears accidentally fell into these traps, injured themselves, and then were forced to take more risks because digging for food items such as tubers and insects would be more difficult with a foot.

Servheen thinks the pain from these traps can also make wounded bears particularly sinister. “We can’t ignore the fact that this is a state of constant suffering,” says Servheen. “If I put a trap like that on my arm and wear it for a week, I’d be pretty miserable too.”

Based on guidance from Lamb and colleagues, BC wildlife officials in 2021 ruled that all body traps set in November must be enclosed in a box with an opening large enough for a marten to curled up, but too small to admit the bear’s paw. Servheen and Lamb also recommended delaying the marten trapping season until early December after most grizzlies hibernate, but those changes have not been implemented.

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