Effects of wetland foraging and body size on bison hair sulfur, nitrogen, and carbon isotope compositions: Implications for wildlife conservation, archaeology, and palaeoecology

Palaeoecological and archaeological reconstructions using stable isotopes rely on understanding isotopic processes in modern ecosystems. This study examines how sulfur, nitrogen, and carbon isotope values ( δ 34 S, δ 15 N, and δ 13 C) of modern plains and wood bison ( Bison bison bison and Bison bison athabascae ) hair records foraging selectivity and size-related metabolic differences in a C 3 -dominated mixed woodland environment: Elk Island National Park (EINP), Alberta, Canada. Terrestrial grasses on the margins of wetlands in EINP had substantially lower δ 34 S and higher δ 15 N than grasses in dry environments, signalling the potential for modern and ancient herbivore tissue δ 34 S and δ 15 N values to record wetland versus dryland foraging. Bison hair δ 34 S and δ 15 N differed between wood and plains bison subspecies, with lower δ 34 S and higher δ 15 N values in wood bison hair suggesting they consumed more plants growing in wetland habitats. Adult females and juveniles consumed a greater proportion of wetland plants than adult males, reflecting differential group dynamics and foraging decisions. Bison body size was positively (linearly) correlated with hair δ 13 C and negatively (non-linearly) correlated with hair δ 15 N, but uncorrelated with hair δ 34 S. We hypothesize that increased body size requires greater reliance on microbial proteins to build body tissues (increasing hair δ 13 C), and that larger-bodied individuals have greater nitrogen use efficiency and lower-quality diets (decreasing hair δ 15 N). Our results suggest that (palaeo)ecological and archaeological researchers should consider the extent to which habitat selectivity and metabolic effects related to sex, age and body size can influence herbivore tissue isotopic compositions. • Sulfur and nitrogen isotopes reflect wetland plant growth and herbivore foraging. • Wood and plains bison diets are high in wetland plants. • Bison dietary selectivity varies with age, sex, and subspecies. • Ruminant gut microbes and nitrogen use efficiency affect hair isotopic compositions. • Isotopic corrections for body size could improve palaeoecological studies.