Short term, but high risk of predation for endangered mountain caribou during seasonal migration

Abstract

Migration occurs over a relatively short time period, but can result in an increased likelihood of mortality. Many populations of Southern Mountain Caribou, an Endangered subspecies in Canada, demonstrate altitudinal migration when moving between alpine and subalpine ranges. These caribou can encounter a high density of predators when transiting low- or mid-elevation valleys. We used camera traps to document the movements of caribou as well as moose, a sympatric ungulate that enhances the distribution and abundance of shared predators, through a mid-elevation valley that was characterized by resource roads and forestry clearcuts. The seasonal occurrence of moose coincided with the migratory movements of caribou (June–September). Similarly, the relative abundance of wolves and bears was greatest when caribou occupied the corridor. We used logistic regression to relate camera images to a range of ecological variables that we hypothesized influenced the seasonal distribution and risk of predation for moose and caribou. The most predictive model suggested that the probability of occurrence of caribou increased with temperature, precipitation, and week of the year. A factor for year revealed that the occurrence of caribou declined over the monitoring period. The most parsimonious model for moose included the same covariates as the most predictive model for caribou. A comparison of the frequency of caribou images with those crossings inferred from GPS-collar data revealed that the camera traps were relatively ineffective at monitoring the migratory movements of caribou. This study provided unique insights into the migration of a declining population of caribou, their interactions with predators, and the limitations of using camera traps to document the infrequent movements of low-density species.