BIGHORN SHEEP

Desert bighorn, one of three living subspecies of bighorn sheep, which once roamed 16 Texas mountain ranges. Their restoration success is important to the ecology of the Trans-Pecos region.

Known for their large horns, desert bighorn males are aged by the “rings” on their horns. They prefer a special type of habitat of high rugged mountain areas with little tree cover. They use the steep mountain slopes to avoid predators. Along the mountain slopes, desert bighorn browse for their food, eating new growth, fruits, and leaves from a variety of woody shrubs.

Desert bighorn range sizes vary considerably across the Trans-Pecos. Along the Rio Grande, bighorn move over hundreds of thousands of acres to acquire the resources they need. Whereas in higher elevation areas, that receive more precipitation, habitat is more connected and bighorn occupy relatively small, stable ranges of only a few thousand acres.

Historically, populations of desert bighorn were thought to number between 1,000 and 1,500 individuals in the late 1800s. By the 1930s population numbers fell to around 300 individuals in only four ranges. By 1960, desert bighorn sheep were gone.

With no bighorn left in Texas, restoration efforts began in the mid-1950s, led primarily by Texas Parks and Wildlife Department (TPWD), Texas Bighorn Society (TBS), and various conservation organizations. These initial labors were primarily in the form of captive propagation, however, they had little success.

In the last 20 years, restoration efforts have been more successful, though. Through exchange programs with other western states and translocations, self-sustaining bighorn populations were reestablished in several of the historically sheep-occupied ranges. Tracking translocated sheep, with the aid of GPS technology, has taught researchers and biologists many factors about their ecology.

Partnerships with agencies and private landowners to provide restoration efforts, is the driving force behind the success of management of desert bighorn sheep in Far West Texas.

Projects

Comparing Release Methods of Desert Bighorn: Survival and Cause-Specific Mortality

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Taylor S. Daily, Carlos E. Gonzalez, Louis A. Harveson, Warren C. Conway, Froylan Hernandez (Texas Parks and Wildlife Department)

This project is funded by: San Antonio Livestock Expo and Texas Parks and Wildlife Department.

Historically, desert bighorn sheep (Ovis canadensis mexicana) were prevalent throughout the Trans-Pecos region of Texas. However, they were extirpated by the 1960s due to unregulated hunting, habitat loss, predation, and disease transmission from livestock. Restoration efforts have been successfully conducted by Texas Parks and Wildlife Department to increase population numbers of resident (i.e., animals that currently populate a region of interest) desert bighorn at Black Gap Wildlife Management Area (BGWMA) through the use of translocations. In winter 2017-2018, we radio collared and released 30 resident (8 Male, 22 Female) and 70 within-state translocated desert bighorn (36 Male, 34 Female) to BGWMA. Of the 70 translocated, 28 (12 Male, 16 Female) were hard released (i.e., translocated animals immediately released onto landscape) and 42 (24 Male, 18 Female) soft released (i.e., released into an enclosure before into the landscape).

Survival and cause-specific mortality has been monitored throughout the duration of the study. Resident desert bighorn had the greatest overall survival (S = 0.87), followed by hard released (S = 0.78), and then soft released (S = 0.62). To date, 26 mortalities (13 M, 13 F) were recorded. Of those mortalities, 4 were residents (15%), 6 were hard released (23%), and 16 were soft released (62%). Soft release is thought to be a better strategy for translocating large mammals, however, for this study it did not improve survival. This is potentially influenced by acclimation time and individual exit strategy from the soft release pen, which should be managed for future restoration efforts.

Updates

For many years BRI has partnered with TPWD to study translocated desert bighorn sheep populations throughout the Trans-Pecos. With this project we are looking into the differences among resident, hard-, and soft-released populations…

“I knew a job that had me inside all the time would not be a good choice. I started investigating careers that had to do with animals and being outdoors. … so when I found out about what wildlife biologists did, I knew that was it.” …