Greater sage-grouse (Centrocercus urophasianus) is a sagebrush obligate bird species found throughout western North America. Over the past 60 years, sage-grouse populations have been declining in many areas due in part to anthropogenic and natural disturbances. In addition to greater sage-grouse, free-roaming horses invasively occupy sagebrush dominated landscapes and have been found to impact rangeland health and availability of natural resources. Free-roaming horse populations have exponentially increased since the passage of the Wild Free-Roaming Horses and Burros Act of 1971. The act protects horses on public lands and allows them to impact the ecosystem in a largely unmanaged way. We hope to identify if horse presence does or does not impact the fitness of greater sage-grouse, as a sagebrush obligate species. The objectives of this study include 1) determining the influence that feral horses have on the abundance of greater sage-grouse in the Great Basin, and 2) identifying the potential influence of herbivory by equines on late brood-rearing habitat. With detailed mapping of sage-grouse habitat and Herd Management Areas (HMAs), we hope to identify specific drivers of lek success or decline, keeping in mind a myriad of factors could be working together attributing to population decline. In Utah, we are focusing on lek sites within and around the Onaqui Mountain, Range Creek, Sulphur, Tilly Creek, and Choke Cherry HMAs. In Nevada, horse and sage-grouse distribution encompasses a wider range, so we are focusing on several randomly selected lek sites with confirmed horse presence for analysis.
Results/Conclusions
Stable and declining sage-grouse leks were identified using data provided by the Utah Division of Wildlife Resources and the Nevada Division of Wildlife. These data were then compared with free-roaming horse location data to characterize the possible influence of horses on sage-grouse populations. In general, many declining lek populations were located in areas with a significant horse presence. GIS and robust field methods are being used to further analyze and compare habitat characteristics. These data will be useful for horse and sage-grouse management to assess the potential impacts of free-roaming horses on sage-grouse habitat suitability. Additionally, these data will be helpful for wildlife management, specifically the BLM (as the entity endowed with the task of managing horse populations on public lands), because if horse presence is indeed found to be a driving factor in sage-grouse population decline, management restrictions may be required to protect the delicate sagebrush ecosystem.