Populations of Greater Sage-grouse have declined across the entire range of the species and habitat loss is considered to be the most important factor contributing to these declines (e.g., Connelly et al. 2004). Agricultural conversion, energy development, feral horses, and livestock grazing are hypothesized to contribute to habitat related threats (Range wide interagency sage grouse conservation team 2012). Substantial research has been completed to assess the effects of energy development (e.g., Walker et al. 2007) and agricultural conversion (e.g., Aldridge et al. 2008), yet, little research has been devoted to understanding the impacts of grazing by feral horses and livestock on sage-grouse demography.
The Sheldon-Hart Mountain Refuge complex and adjacent BLM lands (Vya-Massacre Sage- grouse management area; from here on referred to as Massacre) contain sage-grouse populations that have been subjected to different grazing regimes. We compare areas with no grazing, grazing only by feral horses, and grazing by both feral horses and cattle. Data will be collected from 2013-2016 to augment a historical dataset managed by Dr. Mike Gregg from the Sheldon- Hart Mountain Refuge complex and adjacent BLM lands (Betty’s Butte and Jackass creek) in the 1980s-2000s. Dr. Gregg’s data span the period of livestock removal at Hart Mountain and largely precede invasion of Sheldon by feral horses during the 2000s. Thus, data we are currently collecting combined with those of Dr. Gregg will allow us to examine responses of vegetation and sage-grouse to all possible combinations of grazing by livestock and feral horses.
We assess vegetation responses using vegetation surveys to estimate cover of key vegetation at nests, brood use sites and random points. To evaluate the response of sage-grouse, we develop estimates of female survival as well as seasonal use of habitats, nest survival, and brood survival. The United States Fish and Wildlife Service has conducted aerial surveys to estimate to abundance of feral horses and livestock throughout the study area. In addition, we sampled transects for horse and livestock feces as an index of feral horse and livestock use within areas used by sage-grouse. Our goal is to assess impacts of grazing on vegetation, habitat use of sage- grouse and nonnative ungulates, demographic rates of sage-grouse, and the relationships among these parameters. We assess breeding cost, habitat selection, and limiting ecological factors affecting sage-grouse demographics and movements. We evaluate vegetation characteristics in grazed and ungrazed sites, estimate feral horse and livestock abundance, and build predictive surfaces of sage-grouse, feral horse, and livestock use verses what is available across the landscape.
