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. Reintroducing North America's largest land mammal can have significant ecological impacts, particularly on the species they interact with. Using GPS data, we analyzed space and resource use of a recently reintroduced herd of plains bison to Banff National Park, to investigate potential interactions with another co‐occurring grazing ungulate, the Rocky Mountain bighorn sheep. Comparing the potential for interspecific mechanisms, our study provides further evidence, that where suitable habitat exists, co‐existence between lost species assemblages may be achieved meeting social and ecological goals.