Project Spotlight: Interactions Between Bighorn, Aoudad, and Mule Deer in the Texas Trans-Pecos

Desert bighorn sheep and mule deer have experienced widespread declines in distribution and abundance in the Texas Trans-Pecos. While translocation efforts have been successful in reviving these species, the ongoing expansion of aoudad populations across the region have raised concern for native species survival. Similarities in physiology and native range suggests potential niche overlap (and potential competition) between aoudad, desert bighorn sheep, and mule deer may occur.

The project is a collaborative effort between Borderlands Research Institute (BRI) and Texas Parks and Wildlife Department (TPWD) to investigate these concerns. To do so, BRI and TPWD personnel captured 40 individuals of each species in the Van Horn Mountains of Texas, fitted them with GPS collars, and observed their habitat selection behavior for two years. By comparing habitat selection between bighorn, aoudad, and mule deer, we can evaluate what habitat features are preferred by each species, compare these preferences, and suggest the likelihood of inter-species competition.

We found that aoudad and bighorn sheep displayed very similar preferences for very specific habitat. These results suggest aoudad and bighorn sheep are operating as specialists in the Van Horn Mountains, and that the likelihood for competitive interactions is high. We also found that mule deer had a wider range of habitat preferences that were very dissimilar to aoudad and bighorn sheep. This result suggests the likelihood of competitive interactions between mule deer and aoudad/bighorn sheep to be low in this mountain range.

Using these techniques, we found where preferred habitat is distributed across the Van Horn and adjacent mountains. These habitat maps provide scientists and managers information regarding where we are most likely to see interactions between aoudad and our native species, and to what degree this interaction takes place across the landscape. The implications of this data extend across native species conservation and disease management domains.