Data from: Drivers of spring migration phenology in Rocky Mountain elk

By migrating, ungulates take advantage of cyclical fluctuations in
resources, which allows them to persist at greater population numbers than
they would in the absence of these seasonal movements. We sought to
identify the drivers of spring elk (Cervus canadensis) migration and
evaluate how well individuals were able to optimize access to forage prior
to departure, while migrating, and upon arrival on summer range.
Specifically, we investigated the timing and duration of spring migration
in four Colorado elk herds to test how forage quality and snow dynamics
pre-, during, and post-migration influenced elk departure from winter
range and the length of time spent migrating. Our analyses revealed
significant heterogeneity among and within herds. Overall, spatiotemporal
dynamics in forage and snow emerged as critical drivers influencing
migratory phenology, but the discrete covariates associated with forage
and snow were herd-specific. We did not find marked sub-strategies wherein
some herds or individuals optimized a specific component of migration, but
rather found that elk varied in their ability to optimize access to forage
at all times analyzed. Our findings suggest that elk exhibit a flexible
response to environmental cues, adjusting migration timing and duration in
accordance with local conditions. These results contribute to a deeper
understanding of the mechanisms driving ungulate migration and emphasize
the importance of considering dynamic environmental factors in studies of
migration phenology. Further, they emphasize the importance of forage
conditions not just on the migratory route, but also on winter and summer
range. Additionally, they provide baseline knowledge of elk migrations in
Colorado, useful information for ensuring the conservation and persistence
of these migratory routes and the productivity they facilitate.