Integrating physiological stress into the movement ecology of migratory ungulates: a spatial analysis with mule deer.

David S Jachowski,Brett R Jesmer,Joshua J Millspaugh,Hall Sawyer,Matthew J Kauffman

doi:10.1093/conphys/coy054

Abstract

Rapid climate and human land-use change may limit the ability of long-distance migratory herbivores to optimally track or ‘surf’ high-quality forage during spring green-up. Understanding how anthropogenic and environmental stressors influence migratory movements is of critical importance because of their potential to cause a mismatch between the timing of animal movements and the emergence of high-quality forage. We measured stress hormones (fecal glucocorticoid metabolites; FGMs) to test hypotheses about the effects of high-quality forage tracking, human land-use and use of stopover sites on the physiological state of individuals along a migratory route. We collected and analysed FGM concentrations from 399 mule deer (Odocoileus hemionus) samples obtained along a 241-km migratory route in western Wyoming, USA, during spring 2015 and 2016. In support of a fitness benefit hypothesis, individuals occupying areas closer to peak forage quality had decreased FGM levels. Specifically, for every 10-day interval closer to peak forage quality, we observed a 7% decrease in FGMs. Additionally, we observed support for both an additive anthropogenic stress hypothesis and a hypothesis that stopovers act as physiological refugia, wherein individuals sampled far from stopover sites exhibited 341% higher FGM levels if in areas of low landscape integrity compared to areas of high landscape integrity. Overall, our findings indicate that the physiological state of mule deer during migration is influenced by both anthropogenic disturbances and their ability to track high-quality forage. The availability of stopovers, however, modulates physiological responses to those stressors. Thus, our results support a recent call for the prioritization of stopover locations and connectivity between those locations in conservation planning for migratory large herbivores.

Highlights

Animal migrations serve to bolster fitness by allowing animals to track shifting resource availability and predation risk, while balancing associated locomotive costs (Fryxell and Sinclair, 1988; Alerstam et al, 2003)
In support for our additive anthropogenic stress and physiological refugia hypotheses, we observed a dampening effect of stopover use on fecal glucocorticoid metabolite (FGM), when individuals were sampled in areas of high human disturbance (Fig. 3)
We observed that animals sampled far from stopovers on average were predicted to have 341% higher FGMs in areas of low landscape integrity compared to high landscape integrity (Fig. 4a)

Summary

Introduction

Animal migrations serve to bolster fitness by allowing animals to track shifting resource availability and predation risk, while balancing associated locomotive costs (Fryxell and Sinclair, 1988; Alerstam et al, 2003). These behaviors are increasingly impacted by global change. Climate change has the potential to reduce the ability of large herbivores to accurately track or ‘surf’ gradients of forage quality (Post and Forchhammer, 2008). The ability of animals to accurately track forage quality can be negatively impacted by anthropogenic disturbance. Disturbances along the migration route can negatively impact migratory movements, where animals move rapidly through or avoid areas of high human disturbance (Lendrum et al, 2012; Sawyer et al, 2013)

Methods

Results

Conclusion