Genetic Diversity and Divergence among Bighorn Sheep from Reintroduced Herds in Washington and Idaho

Bison and bighorns: Assessing the potential impacts of reintroducing a large herbivore to a mountainous landscape

The reintroduction of wildlife can have significant ecological impacts by altering the flow of energy in food webs. Recently, plains bison were reintroduced to part of Banff National Park after a 150-year absence. The large herbivore's reintroduction was expected to have far-reaching effects on the ecosystem due to its significant energy requirements and interactions with habitat and other sympatric species. This study explores the impacts of bison reintroduction on the movement and resource use of another large-bodied grazer, the Rocky Mountain bighorn sheep. Between 2018 and 2021, we collected data from GPS collars fit on 39 bighorn sheep and 11 bison. We analyzed home range patterns, resource selection, and interactions to investigate the potential for interspecific competition, facilitation, and resource complementarity. At the population level, bison and bighorn sheep exhibited low levels of spatial overlap and there was strong evidence of resource separation in all seasons. Interactions between species did not appear to affect sheep movement rates; however, we did see differences in forage selection patterns for sheep with overlapping home ranges with bison. Collectively, results did not support the potential for competition or facilitation between bison and bighorn sheep and instead provided the strongest evidence of complementarity.

Restoration of bighorn sheep: History, successes, and remaining conservation issues

Mammals are imperiled worldwide, primarily from habitat loss or modification, and exhibit downward trends in their populations and distributions. Likewise, large-bodied herbivores have undergone a collapse in numbers and are at the highest extinction risk of all mammals. Bighorn sheep (Ovis canadensis) are among those large-bodied herbivores that possess a slow-paced life history, suffer from debilitating diseases, and have experienced range contractions across their historical distribution since the late 1800s. Translocations and reintroductions of these mountain ungulates are key aspects of restoration and often are used to re-establish populations in historical habitat or to supplement declining herds. Millions of US dollars and much effort by state and federal natural resource agencies, as well as public and private organizations, have been expended to restore bighorn sheep. Despite those efforts, translocated populations of bighorn sheep have not always been successful. We assessed restoration of bighorn sheep to provide insights in the context of conservation of populations of bighorn sheep, because this management tool is a frequently used to re-establish populations. We focused briefly on past efforts to restore bighorn sheep populations and followed with updates on the value of habitat enhancements, genetic issues, the importance of ecotypic or phenotypic adaptations when restoring populations, predation, and disease transmission. We also raised issues and posed questions that have potential to affect future decisions regarding the restoration of bighorn sheep. This information will help conservationists improve the success of conserving these iconic large mammals.