Bison movements change with climate: Implications for conservation in the Anthropocene

Nicholas A. McMillan and Samuel D. Fuhlendorf, Natural Resource Ecology and Management, Oklahoma State University, Stillwater, OK, Bob Hamilton, Tallgrass Prairie Preserve, The Nature Conservancy, Pawhuska, OK, Brady W. Allred, University of Montana, Missoula, MT

Background/Question/Methods
Animal movement patterns are significantly affected by the complex interactions between biotic and abiotic landscape conditions, and will be altered by future climate change. Many movement studies have been historically focused on point-pattern analyses. However, much about when or why animals move remains unclear, including how large ungulate movement might respond to climate change. Some wildlife species, like the American plains bison (Bison bison; hereafter bison), are considered keystone species, and their movements can significantly affect landscape biodiversity patterns. our objective for this study was to investigate how bison movement changes according to climate patterns. We specifically set out to test how wind speed, wind direction, relative humidity, rainfall, air temperature, solar radiation, and drought may affect how far bison move on large landscapes. We used long term, fine-scale bison movement and climate data from two large grasslands (12-minute fixes for two years at each) to identify which weather parameters most correlated with movement distance.
Results/Conclusions
Our study consisted of 535,203 total movements from 26 individuals, averaging approximately 1,583 movements per individual, across our two sites in Oklahoma. Of all the weather parameters we tested, we found that air temperature, the air-temperature-solar radiation pairwise interaction, and fractional water index (drought) had the strongest effect on how far bison moved in a 12-minute period. Specifically, bison tended to move further during hotter and drier times than cooler and wetter conditions. When confronted with ambient physiological stress all ungulates are faced with two choices: (1) move to a new place on the landscape where the stress is relieved, or (2) acclimate to the current condition. Our study represents the most robust analysis to date showing that fine-scale ungulate movements, in our case those from American plains bison, may be strongly dependent upon weather. As weather becomes more variable, bison will likely move further and possibly out of allotted conservation areas, potentially escalating ongoing conflict in the Great Plains. Changes in ungulate movement resulting from climate change could influence grassland biodiversity, and future conservation efforts will need to adapt to these changes.