Greater sage-grouse use of thermal refugia on their warm range margin

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Aidan Beers and Nicki Frey, Wildland Resources, Utah State University, Logan, UT

Background/Question/Methods
Climate change is likely to drive widespread species range shifts and extirpations, the first of which will happen mostly on the warm edges of their range. That warm (lagging) range edge tends to be fragmented, with lower quality habitat and lower population density and is more likely to experience threatening weather events. In the Intermountain West, climate will be warmer and drier in the future, driving a reduction in cover of sagebrush (Artemesia sp.) steppe and other shrubland. Among the species threatened by a hotter and more arid climate is the Greater sage-grouse (Centrocercus urophasianus), as they depend on sagebrush for forage and shelter. Other gallinaceous birds are sensitive to temperature extremes and exploit refugia to limit thermal stress. Sage-grouse likely do the same, but their response to temperature is not well studied. We deployed 75 data loggers across two valleys in southern Utah and Nevada and collected temperature and light intensity data every 30 minutes for 27 months. We used those models to test the impacts of temperature, land cover, and topography on sage-grouse habitat selection.
Results/Conclusions
We found that temperature was important informed selection in all seasons and both sites. In Utah, sage-grouse used areas near trees during the summer and winter, likely to avoid extreme heat and cold, respectively. In autumn and spring those extremes were less common and sage-avoided habitat near trees. On the other hand, sage-grouse in the Nevada site were more likely to select large and contiguous patches of sagebrush in extremes periods but only selected habitat near trees in winter cold, avoiding trees during summer heat. Sage-grouse in Nevada also selected moderately heterogeneous terrain during thermal extremes. The difference between Nevada and Utah habitat selection is likely explained by the fact that the Nevada site is at higher elevation and had lower temperatures overall. Our findings show that extreme temperatures drive sage-grouse to select habitat near trees despite the risk posed by avian predators. The difference between our Utah and Nevada sites suggests that sage-grouse likely prefer to use sagebrush as thermal shelter but that it may be inadequate shelter during the hottest times, forcing riskier selection. These models point towards a more mechanistic understanding of how sage-grouse will respond to climate change on warm range margins. This will refine our understanding of seasonal habitat requirements and inform management decisions of how to prioritize thermal refugia for an imperiled species of conservation concern.