Landscape models of space use by desert bighorn sheep in the Sonoran Desert of southwestern Arizona

Abstract

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. Ó 2014 The Wildlife Society.

Extreme drought and adaptive resource selection by a desert mammal

“…Therefore, decision‐making for resource selection involves trade‐offs, whereby individuals must prioritize which beneficial features are of immediate concern, and balance that with minimizing costs imposed by other features. In addition, it should be noted that we investigated only female desert bighorn sheep and that seasonal resource requirements of females may differ from males (Bleich et al 1997, Mooring et al 2003, Hoglander et al 2015). For example, lambing and lactation in desert bighorn sheep can potentially occur anytime from winter through late summer (Rubin et al 2000, Bangs et al 2005 b , Karsch 2014).…”

“…Thus, they are an ideal species for examining the influence of variable climatic conditions on resource selection in desert species. Previous studies of resource selection in desert bighorn sheep have primarily focused on components of the landscape and vegetation associations (e.g., Krausman and Leopold 1986, Hoglander et al 2015); however, abiotic factors in a desert climate likely exert a significant influence on resource selection and should also be considered. Also, species often utilize essential resources for short time periods only, and if an inappropriate sampling period is selected, important habitat components may not be detected (White and Garrott 1990).…”

Seasonal resource selection by introduced mountain goats in the southwest Greater Yellowstone Area

“…Similarly, we hypothesized the squared terms for SLP and ELEV, which allowed the relationship to peak at an optimal covariate value, would also be ranked higher than the linear forms (Gross et al 2002, Poole et al 2009). Evaluating additional functional forms provided more flexibility in determining the most explanatory covariates, and has been shown to improve model fit for previous mountain ungulate resource selection studies (Gross et al 2002, Poole et al 2009, DeVoe et al 2015, Hoglander et al 2015.…”

Conservation implications of using an imitation carnivore to assess rarely used refuges as critical habitat features in an alpine ungulate

“…For example, vegetative cover was once considered the most important habitat feature for elk (Cervus canadensis) to escape human hunters, but it is now clear that limited human access is more central than hiding cover, a result that would not have been detectable in the absence of powerful resource selection models (Proffitt et al, 2013). In other ungulates, such as Dall and bighorn sheep (Ovis dalli, O. canadensis), refuge habitat consists of topographic features-frequently referred to as escape terrain, which specifically has been defined as ''rockland with steep slopes on which individuals can outrun predators'' (Rachlow & Bowyer, 1998;Hoglander et al, 2015). Escape habitat has often been classified vaguely, without actual quantification, which has led to inconsistencies within species.…”