Dietary Overlap of Aoudad, Desert Bighorn Sheep, and Mule Deer in the Trans-Pecos Region, Texas

Olivia Gray, Justin T. French, Carlos E. Gonzalez, Louis A. Harveson, Froylan Hernandez (TPWD), and Shawn Gray (TPWD).

Since the introduction of aoudad (Ammotragus lervia) into Texas, biologists are increasingly concerned with their ecological impacts. Current knowledge indicates potential dietary overlap between aoudad and native ungulates, such as desert bighorn sheep (Ovis canadensis) and mule deer (Odocoileus hemionus). However, biologists know little about the dietary composition of these species in co-occupied landscapes. While all three species eat similar plants, ungulates are known to partition resources when they coexist. Thus, information on each species in isolation is not indicative of how they interact.

To shed light on native ungulates’ response to the presence of aoudad, this project is investigating the dietary composition of co-existing aoudad, desert bighorn sheep, and mule deer. We will locate individuals and obtain fecal and vegetation samples in co-occupied landscapes within the Van Horn Mountains. Fecal sampling takes place monthly over 12 months, collecting five fecal samples per species each month, totaling 180 indivdual samples. We are also collecting all vegetation species within the study area to provide reference images of the plant cell structures for our microhistology library. From the fecal samples we will observe plant cell structures, identifing the vegetation consumed by ungulates.

By examining diets monthly we will determine how dietary overlap changes, identifying key times at which species competition may be most intense. The information gained by this study will aid in the management of ungulates by clarifying the nature and impacts of interactions between aoudad and native species.

Funding sources: West Texas Club of the Safari Club International, San Antonio Livestock Exposition, Desert Bighorn Council, and Texas Chapter of the Wildlife Society.