A unique seasonal migration pattern of threatened caribou in B.C. and Alberta has been fading over decades due to human activity and habitat changes, a 35-year University of British Columbia Okanagan-led (UBCO) study published March 3 has found.
The Global Change Biology study, spearheaded by UBCO wildlife scientist Clayton Lamb with contributions from 16 other researchers at UBC, University of Northern British Columbia, Okanagan College and elsewhere, found that one-of-a-kind seasonal migration of southern mountain caribou between higher and lower elevations declined drastically from 1987 to 2022.
During this period of more than three decades, the southern mountain caribou population shrank by more than half.
With the help of the B.C. and Alberta governments, the researchers spent 35 years monitoring more than 800 caribou with GPS and high-frequency collars across 27 sub-populations where this special elevational migration happens twice per year. Data came from some 1.7 million relocations of the caribou.
While these sub-populations have historically migrated between mountainous areas and lowland forests, based on resource availability, snow conditions and predators, southern mountain caribou's increasing exposure to human-caused landscape disturbances has caused their trademark elevational migration to dwindle and in some ranges stop entirely. These human-caused disturbances across these caribou sub-populations skyrocketed sixfold between 1987 and 2022.
"In most cases, we found that caribou migrated shorter distances and their seasonal ranges were moving upslope over time in such a way that their elevational migrations shrank," the study reads.
Particularly across the five sub-populations of Chase, Columbia North, Columbia South, Bearhole-Redwillow and Redrock-Prairie Creek, caribou's elevational migration nearly collapsed over the 35 years. Old-growth logging is mentioned to have especially reduced the Columbia North and Columbia South herds' movement to lower elevations, shrinking the amount of lichen (their main food source), tree canopy cover and protection from predators.
"Re-establishing this behaviour will be challenging for wildlife managers because it will require the recruitment of mature and old-growth canopies across vast areas, which will take decades," the researchers say.
Human-caused changes to weather patterns have also forced a redistribution of caribou based on where they can continue to access sufficient snow and lichen, the researchers write. The toll taken on numerous sub-populations more generally is evident from the Columbia North herb, for example, which dove from 225 caribou in 1995 to 150 by 2015.
"This post-1987 perspective provides insight into caribou responses during a period of substantial resource extraction and population decline, but also overlooks impacts to caribou occurrence and migration before our study 鈥� during more than a century of landscape conversion following colonization," the researchers add.
The study notes that First Nations have been observing migratory changes to southern mountain caribou since as early as the 1960s, and raised initial concerns about the long-term impacts on herds due to projects such as the flooding of Mica Dam north of Revelstoke in 1973.
Going forward, the researchers conclude that rapid changes to landscape management, extensive habitat conservation and restoration, and reduction of human-caused disturbance will be essential to sustaining the unique range and demography of these caribou.
"It is imperative to conserve southern mountain caribou migratory behaviour from complete collapse," they write.
The study is publicly available at onlinelibrary.wiley.com/doi/full/10.1111/gcb.70095.
