Webinar - Seasonal Patterns of Mortality for Boreal Caribou in the Southern Northwest Territories

Seasonality is an important component in shaping the dynamics that influence ecosystems, including mortality. We investigated temporal patterns of mortality in the boreal ecotype of woodland caribou (Rangifer tarandus caribou) in the southern Northwest Territories. Survival data were collected from 423 adult female caribou tracked by radio collars between 2003 and 2018, 172 of which died during the study from predation (106), non-predation (i.e., starvation), (15), harvest (11), accidents (3), or unknown causes (37). We used generalized additive mixed models to evaluate temporal patterns of mortality across the year. We found that probability of mortality followed a trimodal pattern with three peaks, one during pre-calving, one in mid-summer, and a smaller peak in late autumn, with a 6-fold difference in mortality risk between the lowest and highest periods of the year. Mortality risk was higher overall from late spring (pre-calving) to mid-summer than it was from late summer until the end of winter, despite decreasing for about 6 weeks post-calving. We explored potential factors contributing to mortality risk at different times of the year