Alteration of wide-ranging wildlife migrations can drastically impact the structure and function of ecosystems, yet the causes and consequences of shifting migration patterns remain largely unknown. Decisions made in one portion of a landscape may induce spatial and temporal shifts of wildlife use elsewhere, creating feedback loops that can influence wildlife population sizes and the resources on which wildlife and humans depend. Recent declines in migratory behavior have initiated studies focused primarily on spring migration, which have identified factors leading to a wide range of impacts on migration, from subtle changes relating to plant phenology to drastic switches stemming from land-use change. The timing and benefits of autumn migration have received limited attention due to the difficulty in assessing the extreme asynchrony in autumnal events, although nutrition during this time period is crucial to winter survival and reproduction. Here, we use five years of data from 73 female elk (Cervus canadensis) which utilize a landscape managed by 4 federal agencies, a state, and private landowners, to identify the driving factors behind the initiation of fall migration in two subpopulations, one of which migrates to a protected area where hunting is prohibited.
Results/Conclusions
Most elk departed summer range prior to frost or snow, with 67% of elk that used the protected area migrating prior to the onset of archery hunting season (1 September), preemptively avoiding risk, while no elk from the other subpopulation left prior to archery season. However, departing from productive summer range prior to frost or snow and nearly two months before vegetation senescence to be afforded protection during hunting season decreased access to late summer-fall forage by 21%. Our results suggest that in areas where migratory ungulates span multiple jurisdictions, the benefits of migratory behavior may be dramatically impacted by unevenly distributed anthropogenic disturbance. As this is a common scenario globally, our work highlights the urgent need to improve our understanding of subtle changes in migratory behavior, both spatially and temporally, which may erode the resilience of migration to future change.