Bighorn Sheep Relocation in Sonora, Mexico
Mountain sheep (Ovis spp.) abundance across North America has declined more than 60% from historic times due to factors such as overgrazing, habitat fragmentation, and disease transmission from domestic livestock and exotic species. In Mexico, wild sheep populations experienced unprecedented declines, and by the mid to late 1900s, free ranging bighorn sheep (Ovis canadensis spp.) were extirpated from Chihuahua and Coahuila. Legislation restricted the legal use of wildlife, which indirectly reduced the economic incentive to invest in wildlife conservation. As such, many landowners were financially incentivized to convert their properties to agriculture. In 1997, Mexico established the Wildlife Conservation and Production Diversification in the Rural Sector program, which created a legal framework for private landowners to manage and harvest wildlife under governmental oversight. Only areas registered with the federal Office of Wildlife as Wildlife Conservation, Management, and Sustainable Utilization Units (UMAs) can harvest wildlife through sustainable sport hunting, and UMAs must file a management plan that includes population estimation and monitoring methods, harvest reporting, and protection of wildlife (e.g., protection from poachers) within the property before requesting hunting permits.
The most common tool for restoring bighorn sheep is to translocate a subset of a population to an area either not historically occupied (introduction), previously occupied (reintroduction), or with an existing population (restocking). In Mexico, UMAs are designated as either extensive, in which wildlife is free ranging, or intensive, in which wildlife is managed in a controlled environment (e.g., breeding programs). Currently, 88% of registered UMAs are used for game-ranching and captive breeding. Often, bighorn sheep are raised in breeding facilities and translocated to extensive UMAs to meet the demand for hunting permits while reducing the potential to overharvest resident herds.
Translocated desert bighorn sheep, Sonora, Mexico. Photo courtesy Ivan Lozano. Scan the QR code to see translocated bighorn sheep being released into the Sierra El Alamo Mountains, Sonora, Mexico.
Over 1,000 bighorn sheep reintroduction projects have been conducted across North America; however, only ~50% have been considered successful. Additionally, there is little to no information on the space use, connectivity, habitat use, movement, and survival of translocated bighorn sheep in Mexico, highlighting the importance of working with private landowners to conduct research on free-ranging bighorn sheep. Working with the Artee family, who have a long history of conserving and managing for desert bighorn sheep (O. c. mexicana), our objectives are to quantify space use, connectivity, habitat use, movement, and survival of desert bighorn sheep, which are translocated from an intensive breeding facility (intensive UMA) to a free-range property (extensive UMA) containing a resident, wild population of sheep. We are grateful to the Artee family for partnering with us to conduct research in the Sierra El Alamo Mountains, ~45 km W of Caborca, in northwestern Sonora, Mexico.
In 2022, we captured and fitted 16 desert bighorn sheep (9 F, 7 M) with GPS collars, 9 of which were video collars; these collars collect 1 location every 3 hours. Additionally, we will fit 18 sheep with GPS collars, 1 of which will be a video collar, in May 2024.
Post-release movements of 16 translocated bighorn sheep, Sonora, Mexico. Figure and animation created by Dylan Stewart. Scan the QR code to see an animation of sheep movements following release.
The first leg of the research project is to evaluate space use, movement, and survival. Preliminary analyses of data collected the first year suggest that monthly home range size for females was greatest in April (1,319 ha) and least in September (291 ha). For males, home range size was greatest in February (1,533 ha) and least in October (513 ha). Cumulatively, movement was greatest from April through June (~49 km) for females and from February through April (~52 km) for males. Annual survival (Nov. 2022 – Nov. 2023) was
81% (13/16) for both sexes.
Average monthly range size (ha; Brownian bridge movement model) and movement (km) of female and male bighorn sheep, Sonora, Mexico. Figure created by Dylan Stewart.
Early post-monitoring data suggest the restocking was successful because annual survival was high, translocated sheep joined herds with native sheep, and video collar data suggests females recruited
lambs. We will conduct habitat selection analyses using GPS and video data to identify the factors that influence translocation success, and then use these data to prioritize release and supplemental
water source sites and manage critical habitat across Sonora, Mexico.
To learn more about the project, please feel free to reach out to Dylan Stewart (Dylan.Stewart@tamu.edu), Alejandro Lozano (alejandrolzn@yahoo.com), or Dr. Stephen Webb (stephen.webb@ag.tamu.edu).
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Originally published in the Wildlife Society's Southwest Section Newsletter, Spring 2024 - Vol. 15 Issue #2.
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Authors
Dr. Stephen Webb joined the Texas A&M Natural Resources Institute in November 2021 as a senior research scientist. His research focuses primarily on game and large mammal species such as white-tailed deer, mule deer, elk, domestic cattle and wild pigs, but also has studied greater sage-grouse, northern bobwhite, and several lizard species. He uses advanced and novel tracking and sensor devices, and autonomous recording units, to develop behaviorally and spatially explicit models of animal movement, resource selection, animal interaction, and changes in population demographics.
Prior to joining NRI, Webb worked as a quantitative ecologist for a private natural resource consulting firm in Wyoming. He also worked for a private, non-profit agricultural research institute where he served as manager of ag systems technology and led the range and wildlife ecology research group.
Dr. Webb received his Bachelor of Science and Master of Science degrees from Texas A&M University-Kingsville where he majored in range and wildlife management. He received his Doctor of Philosophy in wildlife science from Mississippi State University.
Stephen is a 7th generation Texan, so joining the Texas A&M Natural Resources Institute is an exciting opportunity to be back home. Outside of work, Stephen spends as much time as possible with his wife and daughter, and also enjoys hunting, fishing and photography.