The Influence of Sulfur and Hair Growth on Stable Isotope Diet Estimates for Grizzly Bears

The study analyzed stable isotope ratios in grizzly bear hair to assess the impact of sulfur (δ34S) on diet estimates, particularly for salmon consumption. The addition of δ34S values slightly improved the precision of diet fraction estimates for salmon and terrestrial prey but added little new information due to strong correlation with nitrogen ratios. The study confirmed some bears consumed marmots and highlighted variability in hair growth timing, suggesting some hair began growing in July or August. Bears with shorter hair consumed more salmon, and hair length influenced δ15N and δ34S values. To capture a complete hair growth period, samples should be collected in late fall, as hair growth timing varied among bears.