EXOTIC

Texas is home to dozens of exotic species, several of which can be found in the Trans-Pecos. These include African species (such as scimitar-horned oryx, gemsbok, and aoudad), Indian species (such as blackbuck antelope and axis deer), and feral hogs.

Aoudad are a hardy desert sheep, native to the coastal and some inland mountains of northern Africa. While considered vulnerable in their native ranges, aoudad are abundant in the mountains of the Trans-Pecos. Little is known about their ecology in their newfound ranges, though considerable evidence suggests that they are susceptible to numerous diseases which affects native wildlife.

Similar to aoudad, feral hogs are highly invasive the Trans-Pecos. Feral hogs must utilize water resources to manage their body heat, which largely limits them to riparian habitats, where cooler temperatures and more moisture make a suitable habitat for them. Unfortunately, these are some of the most sensitive habitats in the region and are inhabited by native species. Also, like aoudad, they are known to carry many diseases, and their wallowing habits have led to contamination of surface water resources.

In particular, aoudad prefer the same rugged, high-elevation habitats as desert bighorn sheep and forage similarly. This combination suggests a competitive relationship, in which desert bighorn are at a reproductive disadvantage. While aoudad breed year-round, most bighorn ewes typically give birth to a single lamb, per year. High reproductive output allows aoudad populations to grow considerably faster than those of desert bighorn.

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The Texas Parks & Wildlife Department, the Borderlands Research Institute, and other agencies have partnered to understand the complex interaction of native and non-native species in the Trans-Pecos. Effective management strategies require an understanding of the mechanisms by which these species interact. Researchers and biologists are currently working to unravel these processes, and provide strategies to minimize the impacts of non-native species to recover native species populations.

Projects

Evaluation of Soil Erosion and Changes in Plant Communities Resulting from Rooting Behavior of Invasive Wild Pigs on the Kerr Wildlife Management Area

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Joshua R. Coward, Bonnie J. Warnock, Ryan S. Luna, Ryan O’shaughnessy, John Kinsey (Texas Parks and Wildlife Department)

This project is funded by: Texas Parks and Wildlife Department, Region 2

Invasive wild pigs (Sus scrofa) are a destructive invasive species that cause an estimated $1.5 billion in combined costs of control efforts and damage mitigation annually. They exhibit foraging behavior that is destructive to soil structure and morphology and disturb the plant communities they occupy. Little research has been conducted in Texas to evaluate how rooting behavior affects soil composition and plant communities after rooting events.

Our objectives for this project include, identifying potential increases in soil erosion after pig rooting occurs, changes in soil texture, moisture content, pH and electrical conductivity, organic and inorganic carbon, nitrogen and bulk densities, and determine how plant communities might change after rooting events. To measure soil erosion, we installed 14 erosion bridges in pig exclosures. These bridges are sampled weekly from January-September of 2018. To determine how soil components are affected, we sampled pig rooting areas to a depth of 15 cm and conducted bulk density samples using the compliant cavity method.

These soil samples are analyzed in a laboratory to determine whether soil components were significantly impacted compared to those of control sites. To determine how plant communities are affected, we sampled vegetation to determine cover class estimates and species presence in rooted areas. These data are compared to previously conducted transects (2016 and 2017). We analyzed vegetation cover classes and presence/absence data to determine how plant communities change after a rooting event.

Evaluating Habitat Utilization by Female Desert Bighorn Sheep and Aoudad in the Sierra Vieja Mountains, Texas

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Jose Etchart, Ryan O’Shaughnessy (SRSU), Jimmy Cain (NMSU), and Louis A. Harveson

This project is funded by: Southern New Mexico Chapter of Safari Club International, West Texas Chapter of Safari Club International, Safari Club International Foundation (SCIF), New Mexico State University, and Borderlands Research Institute.

As our restoration efforts of desert bighorn sheep (Ovis canadensis) continue, anecdotal reports from agency staff, biologists, hunters, and landowners suggest that the desert bighorn is potentially most threatened by the distribution and population increase of aoudad or barbary sheep (Ammotragus lervia). Aoudad, an African generalist originally from the Atlas Mountains in northern Africa, were brought in the United States at the turn of the 20th century. Due to their apparent ease of adaptability there is considerable concern for ecological competition with endemic fauna, and modification of local flora. The effect of aoudad on native ungulates species such as bighorn sheep is unknown.

To determine potential impact aoudad have on desert bighorn sheep. This study evaluated 17 desert bighorn sheep ewes that had been collared in the Sierra Vieja Mountains as part of an ongoing study and 8 aoudad ewes that were collared subsequent the desert bighorn study with GPS radio-collars, to compare habitat selection between both species.

Factors Influencing Survival of Aoudad, Desert Bighorn Sheep, and Mule Deer on a Co-Occupied Landscape

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Daniel Wilcox, Louis A Harveson, Carlos E. Gonzalez, Justin French, Shawn Gray (TPWD), Froylan Hernandez (TPWD)

This project is funded by: San Antonio Livestock Expo, West Texas Chapter Safari Club International, Texas Parks and Wildlife Department, and the Borderlands Research Institute.

The expansion of non-native aoudad (Ammotragus lervia) has been a cause of growing concern among wildlife managers in the Trans-Pecos region of Texas. Given their sympatry with native big game species, it is important to understand potential influences aoudad may have on the sustainability of such species as desert bighorn sheep (Ovis canadensis) and mule deer (Odocoileus hemionus). However, little is known regarding the ecological impact of aoudad in Texas ecosystems. Anecdotal reports suggest aoudad out compete native big game species for food, water, and cover as well as act as a disease reservoir on Texas landscapes. If significant overlap for resources and space are occurring among aoudad, desert bighorn and mule deer, aoudad could outcompete and outgrow native populations. This project was developed to address this concern by investigating survival dynamics of aoudad, desert bighorn, and mule deer in the Trans-Pecos.

Satellite collars equipped with mortality sensors were deployed on individuals of each species in January 2019. In total 41 aoudad, 39 desert bighorn, and 59 mule deer have been collared. These collars allow us to monitor animal movements during the study period and investigate mortality sites to determine cause of death. During capture we also collected blood and tissue samples for disease surveillance. With this information we can compare survival rates between species, cause-specific mortalities, and environmental and disease factors influencing these rates. Results will provide wildlife managers with essential data regarding potential ecological and disease conflicts between aoudad and native species.

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