Project Spotlight: Understanding Pronghorn-Habitat Relationships

Borderlands Research Institute

A male pronghorn in the Marathon Grasslands of West Texas.

Pronghorn (Antilocapra americana) abundance and distribution in Texas have significantly declined from their historical ranges. Habitat declines throughout North America due to fragmentation and degradation have been attributed as a main driver of these pronghorn population declines. Because of this, since 2011, Texas Parks and Wildlife Department (TPWD) and the Borderlands Research Institute have conducted restoration efforts to increase pronghorn populations throughout the Trans-Pecos region of Texas. However, guidelines addressing estimates of carrying capacity and cattle grazing effects on pronghorn-preferred forage are lacking and not well understood. Pronghorn evolved in grasslands with a diet composed of highly nutritional forbs. This preference for specific forbs invokes the term pronghorn-preferred forage. To continue restoration efforts, we need to develop a carrying capacity estimate for pronghorn, as well as a better understanding of how grazing from domestic livestock affects pronghorn-preferred forage production. Having a better grasp on these topics will shed light on pronghorn habitat management techniques needed to bolster the already successful restoration efforts.

Carrying capacity estimates are needed to assess how many pronghorn the habitat can sustain. This estimate will be developed by sampling vegetation during the cool-dry season (January) and the warm-dry season (May) in 2019 and 2020. These two seasons were selected because they are the two most crucial times of the year due to fawning season (May) and a lack of precipitation, which leads to the lowest amount of forage available. Sampling in the Marfa northwest area will be done using 125 1-m2 plots and the Marathon Basin area using 50 1-m2 plots. As in previous pronghorn diet studies, preferred forage species will be analyzed to determine their nutritional composition. Using this prior knowledge and the results of vegetation sampling, we will be able to estimate carrying capacity for each restoration area based on specific forbs consumed during these seasons. Once a carrying capacity has been estimated, we will then look at how different cattle grazing regimes affect pronghorn-preferred forage production to determine how cattle grazing may affect the amount of pronghorn the range can sustain.

To assess the effects of different cattle grazing regimes on pronghorn-preferred forage, vegetation sampling will be conducted in September, the peak of the warm-wet season. This month was selected because it is when the largest amount of forage biomass should be present in the field. Specifically, the study will look at differences in pronghorn-preferred forage production and diversity between rotationally-, continuously-, and non-grazed pastures. To achieve this, random samples will be taken from the grazing regimes using 260 1-m2 plots in the Marfa Grasslands. All forbs in each plot will be collected and analyzed to assess differences in biomass, species diversity, and nutritional composition. Preliminary data was collected in September 2018, and we will continue to conduct data collection in September 2019 to complete a two-year assessment.

The knowledge gained from this study may be used by wildlife biologists and landowners alike to improve habitat management techniques for pronghorn in the Trans-Pecos. The results from this project will provide TPWD with new guidance on where to focus management for future translocation efforts to continue restoring pronghorn populations throughout West Texas.

pronghorn forage table