Researchers find caribou migration patterns are shrinking

Decades of data following the migratory patterns of endangered caribou show that migration areas have decreased significantly. Researchers are concerned that resource extraction is disturbing caribou habitats.

Dr. Clayton Lamb, a researcher with UBC Okanagan’s Irving K. Barber Faculty of Science, led a team that recently published a paper detailing the migration patterns of several threatened caribou herds.

Their study, published this week in Global Change Biology, showed the caribou herds changed their migratory duration, distance or elevation over 35 years of radio tag tracking using very high frequency and Global Positioning System collars.

“Western science and Indigenous knowledge recognize the critical role of migration in sustaining abundant wildlife populations, yet these movements are increasingly disrupted by human activity worldwide,” says Dr. Lamb. “We studied the extent and type of migration as well as changes through time, and determined if these changes correlated with landscape disturbance or shifts in weather.”

The research team, which included representatives from Environment and Climate Change Canada, BC’s Ministry of Water, Land and Resource Stewardship, and Alberta Environment and Parks, analyzed telemetry data for southern mountain caribou from 1987 to 2022.

Study data was collected from 1,704,842 caribou relocations of more than 800 animals across 27 southern mountain caribou subpopulations.

“The data shows that most of these subpopulations remain migratory to some degree, but seasonal migrations appear to be shrinking in both duration and extent,” says Dr. Lamb.

“Though our study spanned just 35 years—a blink compared to millennia caribou have been migrating here—we found migration eroding, not due to weather shifts, but alongside expanding human disturbance and caribou population decline.”

Migrating ungulates, like caribou, follow seasonally available foods, tracking gradients in rainfall, snow depth and safety from predators. Barren-ground caribou in the North American Arctic are known to complete one of the most dramatic migrations, with herds numbering in the hundreds of thousands, including pregnant females, moving 200–500 km each year between seasonal ranges.

While not as dramatic, southern mountain caribou migrations historically occurred vertically, up and down mountains, and horizontally between mountainous areas and lowland forests. But this appears to be changing, says Lamb.

“Due to their southern distribution, these caribou are exposed to higher levels of human-caused landscape disturbance and associated habitat change and loss. Observations from Indigenous communities, local people, scientists and government biologists indicate that southern mountain caribou migrations are changing or not happening at all.”

Dr. Adam Ford, Director of UBC’s Wildlife Restoration Ecology Lab and UBCO’s Institute for Biodiversity, Resilience and Ecosystem Services, is part of the research team and says habitat loss for the caribou is a definite threat to the survival of the species.

“Southern mountain caribou migration, including the distance and elevation change, has declined significantly over the past 40 years, and we believe these changes are correlated with human-caused disturbances, including change and loss to habitat,” he adds.

Dr. Ford noted in 1983, the average per cent of the landscape disturbed by human causes, including logging, reservoirs and oil and gas drilling activity, was about five per cent, while natural disturbance from fire and pests was 0.3 per cent.

By 2020, however, more than 30 per cent of that landscape was disturbed by human behaviour.

“Within the last 35 years, human-caused disturbance increased nearly sixfold within the ranges of the caribou subpopulations. Beyond impacts to migration, habitat disturbance—which has disrupted predator-prey dynamics—is a primary cause of caribou population declines,” says Dr. Ford. “It’s important to note the southern mountain caribou population declined by more than 50 per cent over the period of our investigation.”

Shrinking caribou populations and loss of their migratory behaviour indicate a landscape that isn’t sustaining caribou or their formerly adaptive migratory habits. During the observation period, researchers noted the near collapse of elevational migration for five southern caribou subpopulations.

“Sustaining caribou populations and their migratory behaviour into the future will require a rapid change in managing the landscape that facilitates extensive habitat conservation, restoration and a reduction in ongoing human-caused disturbance,” adds Dr. Lamb.

“Creating a landscape with suitable caribou habitats and lower predator densities that can once again sustain caribou is imperative to preserve their migratory behaviour and support recovery efforts.”