Previous studies have demonstrated the potential of carbon and nitrogen stable isotope analysis (SIA) of feces for use in understanding dietary components and sources. These studies suggest that SIA is useful because it is noninvasive and provides more recent dietary information integrated over a shorter time period than SIA of tissues. We sought to determine whether SIA could be employed in the analysis of feces of American black bears (Ursus americanus) in Utah. Using archived feces, we compared SIA with gross fecal analyses (GFA) to determine if a relationship existed. The percent volume of grass and pine nuts were the only significant indicators of the δ13C of feces. The amount of animal matter was the sole significant indicator of the δ15N value of feces. Although these measures were only weakly indicative (R2 ≤ 0.21), it is interesting that even in an environment that is isotopically homogenous, δ15N and δ13C provided information on the contribution of dietary components. The comparatively tight distribution of fecal δ13C values, essentially ranging −24 to −28‰, clearly indicated a diet of C3 plants. However, this study did not examine the effect of differential digestibility or intestinal slough on δ13C and δ15N values of feces. This needs to be examined. We also encourage additional studies on the usefulness of SIA of feces of omnivores and carnivores. Very few studies exist for these species, and since many of these species are particularly difficult to handle, SIA of feces may provide crucial knowledge of their short-term dietary habits.
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Vol. 22 • No. 2