Investigating local concerns regarding large mammal restoration: group size in a growing population of reintroduced bison (Bison bison)

Group size of gregarious ungulates typically are fluid and may be density dependent. Local people in Yukon, Canada, were concerned that increasing abundance of reintroduced bison (Bison bison) would result in larger groups, leading to increased human-bison conflicts (e.g., property damage, environmental impacts, and aggressive behaviour). Yet, the influence of abundance on group sizes was unknown. To investigate this concern, I used 15 years of group size data (n = 1447 groups) to test the hypotheses that group sizes a) increased with abundance, and b) varied seasonally. To determine the effect of abundance, I assessed summer and late-winter group sizes for three 5-year periods corresponding to a period when the population tripled in size. Neither summer nor late-winter group sizes differed significantly in response to a three-fold change in population density, contrary to my hypothesis and that of local people. Mean and typical group sizes varied seasonally, with those in summer being greatest and those in fall and late winter the smallest. This study provided new information on grouping dynamics of forest-dwelling bison within and between years and demonstrated that group size did not vary in response to a three-fold increase in density, but that there were strong seasonal effects. As such, growing populations of reintroduced bison will likely not result in larger group sizes at the densities observed in this study. The potential for human-bison conflicts may be greatest during summer when bison aggregate. Overall, these data suggest that concerns regarding larger groups due to reintroduced populations growing may not be warranted. Importantly, however, the number of groups on the landscape will increase with population size, and conflicts with local people will likely continue regardless of group size. Acknowledging and addressing the concerns of local people is likely key for increasing their social carrying capacity for reintroduced bison, and successfully restoring them into regional socio-ecological systems. Crown Copyright (C) 2020 Published by Elsevier B.V.