Moose migrations track summer range phenology: Implications for trophic mismatch

Background/Question/Methods

Migratory species time their migrations to the phenology of their seasonal ranges.  As climate change leads to advancing phenology, trophic mismatches can occur when migrants arrive on summer range behind the optimal phenological stage of their food resources.  Ungulate migrations are strongly influenced by climate, and previous work has suggested that trophic mismatches may occur.  The relationship between changing plant phenology and migration timing, however, may differ for short- and long-distance migrants that rely on different environmental cues.  In this study, we evaluated the factors that influence the timing of spring and fall migrations of GPS-collared moose (Alces alces shirasi) that inhabitat the southern portion of the Greater Yellowstone Ecosystem.  We also used patterns of remotely sensed greenness to evaluate the degree to which moose were able to appropriately track phenological changes.

Results/Conclusions

Individual moose showed extremely high fidelity to their summer ranges but not their winter ranges.  The timing of spring migration of individual moose varied by as much as 80 days, and the timing of the fall migration varied as much as 40 days.  Moose occupy summer home ranges across a vast landscape differing in habitat and elevation and appear to initiate their spring migrations to suit their respective summer habitats.  This behavioral pattern was suggested by a strongly negative association between the initiation of spring migrations and the elevation of each animal’s summer range: moose that summered at low elevations departed winter range earlier in the spring than those that summered at higher elevations.  This individual variation in the timing of migration was consistent across years and seasonal migrations, indicating a population consisting of early, average, and late migrators.  In addition, our phenological analysis suggested that moose tend to time their spring migrations so as to arrive on summer range prior to peak phenology when forage plants are most nutritious.  These findings suggest that relatively short-distance migratory herbivores like moose are able to track considerable temporal and spatial gradients in phenology, and that such foraging behavior may also allow them to adapt to phenological changes caused by climate change.