Home is Where the Food is: Causes and Consequences of Partial Migration in Elk

MS Thesis, Kristin Barker (2015-2018)

Migratory and non-migratory ungulates often coexist in partially migratory populations, but the mechanisms that drive and maintain different migratory behaviors within the same herd are poorly understood. In western North America, increasing numbers of elk (Cervus canadensis) reside on low-elevation winter range year-round. These residents can cause issues associated with crop damage, potential for disease transmission to livestock, and reduced effectiveness of harvest management strategies. Because migrants transfer nutrients, alter carnivore distributions, and structure vegetative communities across seasonal ranges, reductions in migratory behavior raise ecological as well as management-related concerns. This work investigated the factors affecting migratory behavior of female elk and assessed the nutritional consequences of different behaviors. In our study of a partially migratory elk population in west-central Montana, we found that migrants had access to lower-quality forage during summer than their non-migratory counterparts. In our broader-scale study of 16 elk herds across western Montana, we found that migratory behavior of individuals was best-explained by a combination of native forage, irrigated agriculture, and conspecific density. Together, these results reveal a strong influence of irrigated agriculture on migratory behavior of elk. Migration is commonly considered a strategy to increase assess to high-quality forage; our results reveal that irrigated agriculture can alter the traditional nutritional benefits of migration by providing high-quality forage at low elevations throughout the year. Although elk were less likely to migrate if they overwintered in irrigated agricultural areas, predictable availability of better forage elsewhere mitigated that effect. Thus, maintaining or improving the quality of forage available on migratory summer ranges should encourage migratory behavior, as should excluding elk from irrigated agricultural areas. Given the importance of nutritional intake during late summer and fall to elk fecundity and calf survival, improving the forage available to migrants could go beyond preserving current behaviors to effectively increase prevalence of migration where irrigated agriculture has subsidized increasing numbers of resident ungulates. 

Learn more:

Barker, K. J., M. S. Mitchell, and K. M. Proffitt.  2019.  Native forage mediates influence of irrigated agriculture on migratory behaviour of elk.  Journal of Animal Ecology DOI: 10.1111/1365-2656.12991. PDF

Barker, K. J., M. S. Mitchell, K. M. Proffitt, and J. D. DeVoe.  2018. Land management alters traditional nutritional benefits of migration for elk.  Journal of Wildlife Management. DOI: 10.1002:jwmg.21564. PDF

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