Pronghorn Dietary Selection as a Response to Livestock Grazing Systems in the Trans-Pecos, Texas

Leanna S. Morin, Justin T. French, Carlos E. Gonzalez, Louis A. Harveson, and Shawn S. Gray (TPWD)

The pronghorn (Antilocapra americana) is an ungulate native to North America, ranging from southern Canada to northern Mexico. Pronghorn populations in the Trans-Pecos region of Texas once numbered 17,000 individuals, but have declined in the last two decades as a result of drought, disease, habitat degradation, and fragmentation. Additionally, human development and changes in land use have resulted in shrub encroachment, promoting decreased quality and quantity of forage, thereby intensifying the loss of pronghorn populations.

To mediate population declines, the Texas Parks and Wildlife Department and partners began translocations and habitat improvements in 2011. Given that pronghorn forb identification is not well represented in diet literature, it is important to document what vegetation species pronghorn select and why they choose one forb species over another. This allows managers to assess forage quality of a given habitat.

In 2021 and 2022, we will collect 50 random fecal samples in the Marfa Plateau on the Mimms Ranch beginning in January during the cool season and then again in September during the warm-wet season. Fecal samples will be dried, ground, and examined for species-specific plant material using microhistological procedures. We will also collect 350 random 3.280 ft vegetation plots using a Daubenmire frame. Because pronghorn strongly prefer forb species, we will identify and collect all forb species rooted within the frame to analyze their biomass, energy, moisture content, and protein composition.

Comparing fecal and forb community composition between the two seasons will reveal any differences in vegetation quality, quantity, and changes in forb selection. Understanding pronghorn diet patterns and forage selection processes are imperative for conserving this diminishing species. Elaborating on the links between pronghorn forb choice, nutrition, and seasonality in the Trans-Pecos can help land managers and biologists assess habitats for future pronghorn restoration efforts.

Funding sources: San Antonio Livestock Exposition and Texas Parks and Wildlife Department.