Wolf reduction boosts caribou survival—but only in rugged terrain

Reducing wolves to protect endangered caribou doesn’t always deliver the expected results—and the shape of the land may be the deciding factor.

That’s according to research led by doctoral student Tazarve Gharajehdaghipour and professor Dr. Cole Burton in the faculty of forestry and environmental stewardship, which examined newborn caribou survival in Itcha Ilgachuz Park in west-central B.C.

Using GPS collars to track animals, the team found that B.C. wolf removals boosted calf survival in steep, mountainous terrain, but made no difference in flatter terrain.

“This study is a note of caution,” said Dr. Burton. “Different herds face different conditions. Wolf control may not be reducing calf mortality as effectively as we once thought.”

How land and predators affect calf survival

The key factor is which predators can catch calves at different ages. Bears and wolverines can hunt newborn calves in the first two weeks, but can’t catch older, more mobile calves. Wolves, by contrast, can catch the older, faster calves.

In rugged areas, this makes a big difference. Bears and wolverines can kill newborns at high elevations, but by the time mother–calf pairs move down to valleys at around three weeks old, the calves are too fast to catch. At this stage, wolves become the main threat.

Before wolves were removed, most calf deaths occurred during this period. Removing wolves eliminated this later cause of death, boosting survival by 41 percentage points—because bears and wolverines cannot hunt the older calves effectively.

In more accessible areas, wolves can reach calving sites throughout the season, including early when calves are young and vulnerable. When wolves were removed, other predators, such as bears and wolverines, simply killed more of these young calves, so overall survival did not improve.

Tracking calves through mothers’ movements

This is the first study to use GPS collars to follow newborn mountain caribou survival. The research builds on tracking methods developed by co-author Dr. Marie Auger-Méthé, a UBC associate professor in the Institute for the Oceans and Fisheries and department of statistics. 

They found clear patterns: mothers abruptly start moving less when giving birth to stay close to newborns, then gradually increase activity as calves get stronger, or quickly return to normal movement if a calf dies.

“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.

The caribou collar data, which this research paper is primarily based on, was collected by B.C. government biologists, and secured through open access. 

Conservation beyond predator control

The research also found that calf deaths before wolf reduction—likely caused by wolves—were linked to horseback and ATV trails and treed valleys. This suggests wolves use these areas to reach calves. Limiting trail development could help reduce wolf-caused deaths in places where wolf control isn’t used.

While B.C.’s wolf reduction program now covers 15 caribou herds, Dr. Burton emphasizes it’s critical to protect habitat.

“If wolf control is sometimes ineffective and diverts attention from habitat restoration, it’s a real concern,” he said. “Without recovering habitat, you’d have to keep controlling wolves indefinitely.”

The researchers recommend that wildlife managers consider the landscape, predator communities and habitat conditions before starting wolf control programs. They also encourage using GPS tracking and camera traps to better understand calf survival across B.C.

Tazarve Gharajehdaghipour 
Doctoral student, Faculty of Forestry and Environmental Stewardship