February 10, 2016


Article originally appeared on the Safari Club International Foundation's "First For Wildlife" blog

http://www.sulross.edu/sites/default/files/sites/default/files/users/images/news_pubs/pronghorn_capture_0_0.jpgSCI Foundation is supporting a new project examining competition among aoudad and bighorn sheep in the Trans-Pecos region of west Texas. Thank you to the West Texas and Southern New Mexico SCI Chapters for contributing to this research project! SCI Chapters around the world conduct wildlife research and conservation projects. Seven other Matching Grants were recently funded by the Foundation.

Aoudad and Desert Bighorn Sheep Project Report by Jose Etchart and Dr. Ryan O’Shaughnessy

Over the years, much speculation has been directed at the interactions of aoudad and desert bighorn sheep (DBS). Advocates of DBS sheep claim aoudad outcompete DBS in native ranges, thereby causing a decline in population. Conversely, proponents of aoudad support the notion that these species utilize clearly defined niches, and that no competition exists between the animals. Most of the current information regarding interactions between these species is anecdotal and speculative.

Concerns were highlighted at the recent Desert Bighorn Council Meeting held in April, 2015 at Borrego Springs Resort, California. Various state wildlife agencies, biologists, and managers looked to Texas to provide answers regarding aoudad/bighorn interactions.

Unfortunately very little, if any, scientific evidence exists examining direct competitive interactions between aoudad and DBS. As a result, the Borderlands Research Institute at Sul Ross State University in partnership with Texas Parks and Wildlife Department initiated a research project aimed at determining the level of interaction between these two species.

Funding for this project was provided by donations made by the Southern New Mexico Chapter and West Texas Chapter of Safari Club International, and through a matching grant support provided by Safari Club International Foundation (SCIF). Without the support of these chapters and SCI Foundation this research would not be possible.

In September, 2015 the Borderlands Research Institute captured and collared 12 aoudad via a net-gun fired from a helicopter. Aoudad were captured from the Sierra Vieja Mountain Range in far west Texas, and fitted with tracking collars. These collars should remain on the aoudad for the next 2 years before being automatically released from the sheep. These collars will use GPS to record the location of the individual every 4 hours. This location data is however only available once the collars have been retrieved, therefore the aoudad are also located weekly via the VHF signals emitted from the collars. Additionally, mortality can be detected via the collar’s mortality mode, which is activated when the collar is stationary for more than 8 hours.

There have been no mortalities on the collared aoudad to date, thus no collars have been retrieved from which to analyze location data. The collars are expected to automatically release from the aoudad during September 2017.

At the time of collaring aoudad, 24 desert bighorn sheep (DBS) retained VHF/GPS collars attached as part of a companion study. We expect to retrieve collars automatically detaching from DBS during February 2016. The information gleaned from both the aoudad and DBS should allow us to compare movements, home range use, survival, and the level of competition experienced between the two species.

We have been collecting fecal pellets from both species to determine if DBS and aoudad are competing for dietary resources. Fecal pellets are collected during all 4 seasons. A total of 34 samples (each sample representing an independent herd) have been collected to date, 19 being aoudad samples and 15 being bighorn samples. Once done with winter season collections, we will begin to analyze the extent of dietary overlap between the species.

Trail Cameras were placed at 9 artificial water sources found on Capote and Escondido Mountains within the Sierra Vieja Range. Cameras were mounted on camera stands or T-posts and attached 2 feet above the ground and set to be active 24 hr/day. Cameras are set to a 2-picture burst to increase probability of identifying an animal and have a 5 minute delay after each burst. Each camera records the date and time of all photos taken. Since this part of the project is also part of a companion DBS study, camera trapping began in March 1, 2014 and will continue to March 2017. Cameras are being checked every 2 weeks and photographs analyzed for each monitored water site.

To date, we have been able to determine both species have similar lambing periods, although aoudad appear to have a far more protracted lambing period compared to DBS. We are continuing our investigations using camera traps and hope to determine if aoudad and DBS use water sources differentially, and if one species excludes the other from access to water.

Results of this research project will be applied to improve the management strategies of desert bighorn sheep and aoudad populations in the region.

To learn more about related research, visit our Desert Bighorn Sheep Research Page, or view bighorn sheep videos, on our YouTube Page.