Landscape Models of Space Use by Desert Bighorn Sheep in the Sonoran Desert of Southwestern Arizona

The desert bighorn sheep (Ovis canadensis mexicana) is one of the few ungulates native to North America capable of surviving in harsh desert environments and xeric conditions. However, the effects of an increasingly arid climate on this species and its habitat are unknown. We sought to identify important predictors of desert bighorn sheep diurnal space use to provide new insight into management and conservation opportunities. We evaluated home range size and relative intensity of space use for 41 collared individuals monitored between 2007 and 2010 across a 14,217-km(2) extent of Arizona's Sonoran Desert, including the Kofa National Wildlife Refuge and the United States Army Yuma Proving Ground. Using linear mixed models and an information-theoretic approach, we developed seasonal models of intensity of space use for the summer (Jun-Aug) and non-summer (Sep-May) seasons. Models included environmental variables representing escape terrain and distance from developed waters, and Normalized Difference Vegetation Index metrics that represented forage and preformed water resources. We found intensity of space use to be greater for females (than for males) in the summer season and smaller home range sizes for both sexes in the summer season. Escape terrain was the dominant predictor of intensity of space use in both seasons, but forage and preformed water resources were strong predictors only in the non-summer season. These results likely reflected a seasonal trade-off between escape terrain (i.e., predator avoidance) and limited forage and water resources, particularly for more risk-averse females. Effective conservation and management strategies for desert bighorn sheep should consider the availability of both quality forage and water resources in areas of escape terrain. Although more research is needed on species-specific vulnerabilities to climate change and drought, our approach to integrating vegetation indices into estimates of space use is highly transferable to analyses of other wide-ranging species occupying dynamic arid environments. (c) 2014 The Wildlife Society.