PRONGHORN

Pronghorn are the last members of a unique family of North American mammals (Antilocapridae). Neither a deer, nor a true antelope, pronghorn are icons of the western prairies. They are the second fastest land animals and have the only true horns that fork, which they shed and regrow annually.

Pronghorn are highly selective foragers. Forbs, which are fleshy flowering plants, make up over 60% of pronghorn diets in the Trans-Pecos. However, pronghorn are highly selective among forb species, selecting the best parts of highly nutritious species. Important forbs include Filarees, Milkworts, Daleas, Evening Primroses, and Globe Mallows.

However, pronghorn must move to find these relatively scarce resources, relying on speed to avoid predators. Thus, the ability to move freely across the landscape is critical for pronghorn survival. While they can jump, pronghorn do not jump over fences, but instead, duck under them. Fences reduce the habitat area for pronghorn, increasing mortality risk.

Populations of this unique mammal have seen better days. Historically, pronghorn in Texas ranged as far east as Interstate 35 but are now restricted to the Trans-Pecos, Panhandle, western Edwards Plateau, and southern Rolling Plains regions. The Trans-Pecos region once supported 60-70% of the state’s pronghorn, with numbers reaching a high of 17,000 animals during the mid-1980s. By 2012, the Trans-Pecos population reached a historic low of approximately 2,700 individuals.

In 2010, concerned landowners partnered with the Texas Parks & Wildlife Department (TPWD) and the Borderlands Research Institute to investigate the causes of pronghorn decline and take actions to reverse it. Since 2011, pronghorn translocations and restoration efforts have informed researchers and biologists on to developing management strategies to increase habitat connectivity, forage production and quality, and facilitate pronghorn survival.

Projects

Developing Pronghorn Carrying Capacity Estimates for Trans-Pecos, Texas

july2018

Jacob C. Locke, Carlos E. Gonzalez, Justin T. French, Louis A. Harveson, Shawn S. Gray (Texas Parks and Wildlife)

This project is funded by: Texas Parks and Wildlife Foundation and the Houston Livestock Show and Rodeo

Texas Parks and Wildlife Department has engaged in pronghorn (Antilocapra americana) restoration efforts since 2010 to bolster the declining Trans-Pecos population. These efforts focused on restocking ranges that historically supported large numbers of pronghorn. However, population targets remain vague in the absence of an estimate of the population size available habitat can support. Because of this, we undertook efforts to estimate pronghorn carrying capacity in two restoration areas; the Marfa Northwest management unit (~216,190.23 ac) and the Marathon Basin (~64,660.07 ac).

We conducted vegetation sampling during the cool-dry and warm-dry seasons of 2019 and 2020. These seasons represent key times when available forage may limit population performance. We restricted sampling to forb species, as these account for approximately 85% of annual pronghorn diets. We also restricted sampling to grassland habitats within the two areas, reducing our study areas to 187,081.01 ac (Marfa Northwest) and 34.204.33 ac (Marathon Basin). We randomly sampled the two areas using 125 (Marfa Northwest) and 50 (Marathon Basin) plots. We collected all forbs in each plot to estimate forb biomass. We then estimated forage carrying capacity based on a daily intake rate of 3.60 lb/day per pronghorn. We hypothesized our carrying capacity estimates would exceed the current population numbers of 145 (Marfa Northwest) and 479 (Marathon Basin), with Marfa Northwest being further from carrying capacity compared to the Marathon Basin.

We estimated carrying capacity to be 1,231 (Marfa Northwest) and 734 (Marathon Basin) individuals in the cool-dry season of 2019, based on a 25% harvest efficiency. Estimates in the warm-dry season of 2019 were 1,640 (Marfa Northwest) and 623 (Marathon Basin) individuals, also based on a 25% harvest efficiency. The results of this study will provide information needed to set measurable management targets for continued restoration efforts.

Seasonal and Acclimation Period Movements of Translocated Pronghorn in the Trans-Pecos Region of Texas

BN_2017_11

Howell Pugh, Carlos E. Gonzalez, Dana Karelus, Louis A. Harveson

This project is funded by: Texas Parks and Wildlife Department and Texas Parks and Wildlife Foundation

Due to decline in pronghorn populations in the Trans-Pecos, a group of concerned stakeholders formed the Trans-Pecos Pronghorn Working Group (TPPWG) in 2009. The TPPWG focus was to determine reasons for the decline and implement solutions to ensure the recovery of the Trans-Pecos population. It was determined by Texas Parks and Wildlife Department, TPPWG, and Borderlands Research Institute, that the Trans-Pecos population would not recover on its own and that a large-scale translocation would be needed to aid the recovery. In response to the declining population, a translocation effort began in 2011. An additional 4 translocations have since occurred, moving 668 pronghorn to the Trans-Pecos. Thirty to 60% of the adult female pronghorn were fit with GPS collars during each translocation.

The objective was to assess the home range and acclimation movements of translocated pronghorn using GPS data from radio-collared animals in the Marfa Plateau and Marathon Basin during four timeframes; acclimation period, peak fawning period, dry season, and wet season. We have used kernel density estimator and generalized linear models and a linear mixed model to test differences between translocations. No difference was found in home range sizes in either the acclimation or the peak fawning periods but did find dry season home ranges larger than in the wet season. Home ranges of translocated female pronghorn documented indicate the need for future conservation and habitat management at a large scale.

Updates

The panoramic horizon was broken by a red Robinson R44 helicopter. Below it, precious cargo. Two of the Chisum Ranch’s many pronghorn dangled under the chopper like wind chimes. The pronghorn came in for a soft landing, and a group of wildlife professionals quickly huddled around them…

“I feel incredibly privileged to get to do what we do…. Helping to bring back one of Texas’ most iconic big game species to its native range is a pretty cool feeling.”…

In the Trans-Pecos, carrying capacity estimates are needed to assess how many pronghorn the habitat can sustain. We are also studying how different cattle grazing regimes affect pronghorn forage…