Certain caribou herds in British Columbia (B.C.) are endangered. And in an effort to protect caribou calves from wolf predation, the B.C. government has implemented a wolf-removal program that could help stabilize caribou herds.
However, a study published in The Journal of Wildlife Management found that while predation by wolves has been reduced in certain terrain, the removal of wolves did not reduce calf deaths in others.
“This study is a note of caution,” said Cole Burton, a professor with the University of British Columbia’s (UBC) faculty of forestry and environmental stewardship, in a press release. “Different herds face different conditions. Wolf control may not be reducing calf mortality as effectively as we once thought.”
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How Caribou Calves Evade Predators
Phototrap image of mom and baby caribou
(Image Credit: Cole Burton, UBC Forestry & Environmental Stewardship/CC BY-SA)
The research team, which also includes doctoral student Tazarve Gharajehdaghipour, analyzed caribou populations within B.C.’s Itcha Ilgachuz Park. The primary predators for caribou calves are wolves, bears, and wolverines. And a calf’s age determines how easily it can be preyed upon.
When calves are first born, they are much less mobile during their first two weeks of life, making them easier for bears and wolverines to catch. During this time, the calves and their mothers live in higher, more rugged terrain.
Once the calves reach about three weeks old, though, they descend to lower, flatter elevations, where they become much more mobile and can evade predation by bears and wolverines. This is not the case with wolves, which can easily catch a caribou calf regardless of the age.
According to the study, before the wolves were removed from one calving area in rugged terrain, most calf deaths occurred after they were 3 weeks old. By removing wolves from the rugged area, calf survival increased by 41 percentage points.
But in more gradual landscapes, with the wolves gone, wolverines and bears simply killed more of the younger calves, so the overall calf survival rate did not improve.
Tracking Caribou Behavior Through GPS
According to the study, this is the first time researchers have used GPS collars to track the survival of newborn mountain caribou, and it was developed in part with Marie Auger-Méthé, a UBC associate professor in the Institute for the Oceans and Fisheries and the Department of Statistics, and a study co-author.
Through the GPS collars, the team tracked clear patterns, as mothers began to move less and gave birth, stayed near their calves, showed an increase in activity as their calves grew stronger, and returned to normal movement patterns if their calf died.
“This method lets us watch the critical first four weeks of life, when calves are most at risk. We also used camera traps to see when predators were on the calving grounds,” said Gharajehdaghipour in a press release.
Landscape Management Could Be More Effective
While wolf-related caribou calf deaths decreased in rugged terrain, the wolf reduction program did not improve calf survival in flatter, more accessible landscapes.
According to the study, wolf predation on younger calves, before the program, may have been easier due to more accessible landscapes created by ATV and horseback trails, as well as tree-covered valleys. The researchers suggest that wolves used these features to reach calves. Limiting certain trail development may help reduce wolf-involved calf death in places where the reduction program is not being used.
The wolf reduction program covers 15 caribou herds; however, it may be negatively affecting habitat restoration.
“If wolf control is sometimes ineffective and diverts attention from habitat restoration, it’s a real concern,” Burton said. “Without recovering habitat, you’d have to keep controlling wolves indefinitely.”
The research team recommends assessing predator communities, habitat conditions, and landscape conditions before implementing programs like the reduction program. They also recommended using GPS tracking and camera traps in herds to better understand calf survival.
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