Spatiotemporal mapping of the usable space of free-roaming equids across the western United States: A simple yet efficient approach with implications for monitoring

Authors: Hernandez, Alexander; THACKER, ERIC - Utah State University; PATTEN, KADEN - Utah State University; STONER, DAVID - Utah State University

Submitted to: Wildlife Society Bulletin
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/3/2025
Publication Date: 3/23/2026
Citation: Hernandez, A.J., Thacker, E., Patten, K., Stoner, D. 2026. Spatiotemporal mapping of the usable space of free-roaming equids across the western United States: A simple yet efficient approach with implications for monitoring. Wildlife Society Bulletin. Article e70015. https://doi.org/10.1002/wsb.70015.
DOI: https://doi.org/10.1002/wsb.70015

Interpretive Summary: Rangelands in the western United States are subject to multiple landscape-level ecological pressures such as frequent wildfires, invasion by non-native plant species, land use changes, recurrent droughts, among others. Free-roaming equids (i.e. horses and burros) also contribute to the pressures that delicate rangelands experience as these are large, highly-mobile animals that roam over large expanses of land and require considerable quantities of forage and water for their survival. We developed maps of the space that these animals have actually used across the western U.S. states for a period of time that spans from the mid 1980’s to the early 2020’s. The maps were prepared following a rather simple approach of intersecting freely available online datasets that describe the availability of forage and the accessibility to water resources throughout time and space across the U.S. These maps can help a variety of stakeholders such as ranchers and farmers to identify and monitor different quality (i.e. low, medium and high) levels of the usability of the space that free-roaming equids occupy across the western United States.

Technical Abstract: Management of wild equids in the American West is hindered by the lack of a formal habitat map and monitoring system. To address this need, we developed a simple method that is based on annual metrics of water accessibility and forage availability to map the dynamic rangelands where free-roaming equids (FRE) are found in the western United States. The usable space as described here was mapped for the entire spatial domain of the Bureau of Land Management (BLM) managed Herd Management Areas (HMA) covering an area of 107,434 km2 and a time series that spans 1984 to 2021. We then ranked the usable space in three simple categories representing high, moderate and low-quality habitats. The resulting maps have high reliability by showing a high temporal correlation with the FRE aerial population surveys that the BLM conducts on a rolling basis across the west. These maps can be used for monitoring changes in habitat, and detection of degradation/enhancement for each individual HMA on an annual basis. Lastly, we ranked the mapping units based on their resilience to changes in precipitation and therefore the ability to maintain greater proportions of high-quality habitats across time.