Remote Sensing of Snowscapes and Caribou (Rangifer tarandus) Movement in the Northwest Territories of Canada

Recent studies probe that snow characteristics may be primary drivers of migration, largely due to caribou's high level of mobility and their dependence on landscape conditions for locomotion. To investigate whether and how snow characteristics such as melt/refreeze status and the presence of ice are related to caribou movement, we used GPS (Global Positioning System) tracking collar data provided by the Government of the Northwest Territories' Department of Environment and Natural Resources to identify individual animal location and migration patterns, with a focus on the Bathurst herd. We analyzed 117 individual female caribou with more than 30,000 observations between 2007 and 2016 from the Bathurst herd in the Northwest Territories of Canada. We used a hierarchical model to estimate the beginning, duration, and end of spring migration and compared these statistics against snowpack characteristics (i.e., the timing of melt onset and melt/refreeze cycles) which we derived from37 GHz vertically polarized (37V GHz) Calibrated, Enhanced-resolution Brightness Temperatures (CETB) at 3.125 km resolution. We found that the start of spring migration is closely associated with the timing of melt onset and is most often preceded by snow melt onset by just a few days. Melt onset and the start of migration proved very closely associated when plotted across all years, suggesting that melt onset events provide either triggers for migration or favorable conditions that increase mobility. A causal relationship between snowmelt timing and caribou migration would allow for anticipation of caribou migratory behavior and potential shifts in herd ranges.