Caribou migration patterns disrupted by human activities
An extensive, decades-long analysis tracking endangered caribou populations has revealed that migration patterns are eroding in both distance and duration. Researchers attribute this decline largely to human-caused habitat disturbances rather than shifts in climate.
The work, led by Dr. Clayton Lamb of University of British Columbia (UBC), emphasizes the urgency of safeguarding caribou habitats and their time-honored migratory routes.
“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,” Lamb said.
“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.”
Shrinking caribou migrations
The research team examined data spanning 35 years (from 1987 to 2022), which included 1,704,842 geolocation points from radio tags and GPS collars. More than 800 individual animals across 27 southern mountain caribou subpopulations provided a massive dataset.
By comparing the timing and distances traveled over three and a half decades, scientists gleaned new insights into how caribou movement is shifting.
“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,” Lamb said.
“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.”
Caribou have traditionally migrated in response to food availability, snowpack conditions, and predation pressures, using both elevational (vertical) and horizontal movements.
Barren-ground caribou in the far north, for example, routinely traverse hundreds of kilometers, sometimes in vast herds. Southern mountain caribou travel smaller distances, but they once performed significant up-and-down journeys among mountainous and forested regions.
Human-caused habitat disturbance
While the researchers tested the influence of changing weather patterns, they found no significant correlation between the shifts in migration and climate variables. Instead, they identified industrial and resource development as the primary factor affecting migration routes.
“Due to their southern distribution, these caribou are exposed to higher levels of human-caused landscape disturbance and associated habitat change and loss,” explained Lamb.
“Observations from Indigenous communities, local people, scientists and government biologists indicate that southern mountain caribou migrations are changing or not happening at all.”
Signs of development – such as logging, oil and gas extraction, road-building, and other infrastructure projects – have transformed much of the caribou’s original habitat.
By subdividing forests and carving out new corridors, these changes can boost predator access and fragment the terrain, making traditional migratory routes untenable.
Significant decline in caribou migration
“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,” said Adam Ford, director of UBC’s Wildlife Restoration Ecology Lab.
In 1983, just 5% of the area inhabited by these caribou subpopulations had been disturbed by human activities (like reservoirs, logging, and resource extraction), whereas natural disturbances – for instance, from fire or pests – accounted for a mere 0.3%. By 2020, however, more than 30% of the same landscape had been altered by human use.
“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,” Ford said.
“It’s important to note the southern mountain caribou population declined by more than 50 per cent over the period of our investigation.”
This steep population drop coincides with the observed erosion of migratory behavior, signaling that caribou now struggle to adapt to an environment fragmented by industry.
Restoring ecological balance
“Sustaining caribou populations and their migratory behavior 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,” Lamb said.
Consequently, the study suggests that reversing these trends will require robust habitat protection efforts and stricter oversight of resource extraction.
Creating buffer zones, reforesting clear-cut areas, and adopting management strategies to limit predator access are essential steps.
“Creating a landscape with suitable caribou habitats and lower predator densities that can once again sustain caribou is imperative to preserve their migratory behaviorr and support recovery efforts,” Lamb concluded.
Experts agree that a sustained effort to restore ecological balance could keep caribou on the move. Without prompt and meaningful intervention, further disruptions could eliminate both the migration patterns and the herds themselves – losing a millennia-old aspect of the mountain ecosystem.
Through collaboration among governments, industries, local communities, and Indigenous groups, conservation initiatives may still preserve this species’ ancient migratory legacy.
The study is published in the journal Global Change Biology
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