Seasonal migration in terrestrial herbivores presumably confers fitness benefits if it promotes resource tracking in space and time. Interannual variation in the timing of availability of forage resources across the spatial domain may, however, pose challenges for resource tracking in species that undergo long-distance migrations cued by factors other than those that drive resource phenology. Such challenges may be particularly acute in the Arctic, where variation in plant phenology in time and space is strongly associated with abiotic factors that are changing rapidly. Here, we explore the dynamicity of green wave phenology with respect to its implications for caribou arrival timing on a summer calving range in southwest Greenland. We investigate a suite of candidate environmental variables as drivers of green wave dynamics, and analyze the relationship between interannual variation in annual green wave presentation and that of caribou migration phenology.
Results/Conclusions
The direction of annual green wave development is highly variable among years, and, contrary to expectation, most often unfolds against that of caribou migration. Despite considerable interannual variability in both the onset and direction of the green wave, caribou migration phenology ultimately operates independently of plant phenology or other environmental factors. Accounting for the negative autocorrelation in caribou arrival timing reveals that environmental variables and population size drive negative autocorrelation in migration phenology, but do not ultimately drive migration phenology itself. Additionally, no long-term trend is detected in arrival timing, suggesting that caribou migration phenology ultimately relies on a photoperiodic cue. Given current forecasts for annual tundra green-up phenology, interannually consistent caribou migration could lead to an expansion in spatiotemporal mismatch in space use relative to resource availability.