Mountain Caribou Herds Heading for Extinction

Several subpopulations of mountain caribou in British Columbia, including three with fewer than seven individuals in 2002, face imminent extinction.

Since 1992, southern herds generally declined, some dramatically, while several northern subpopulations remain relatively stable.

Despite high pregnancy rates, calf recruitment is insufficient to offset adult mortality in many southern BC herds. For example, annual adult survival rates averaged 0.55 in the Purcell-South subpopulation during the 1990s, while calf recruitment was below 6 percent annually. Consequently, the herd comprising 63 caribou in 1995 dropped to 16 animals in 2002.

Several subpopulations do have annual adult survival rates ranging from 0.84 to 0.93, which is considered common for woodland caribou, of which mountain caribou is an endangered ecotype. Overall, BC's annual calf survival averages 12 percent, which falls within the range found in stable caribou populations, but varies from 0 percent to 23 percent among the subpopulations.

Predation during spring and summer is the main cause of mortality, primarily by cougar in the south and wolves in the north. Bears are also significant predators across the range, and to a lesser extent, wolverine. This has led to BC's woodland caribou fragmenting into isolated subpopulations along the edges of their contracting range.

Researchers suspect that caribou predation has increased because of major ecosystem-wide changes in large mammal predator-prey dynamics. Gains in deer, elk and moose populations have resulted from successful game management strategies and the expansion, by forest harvesting, of early seral habitat. This boosted predator numbers, which predator management policy has left unchecked.