Figure 2. Annual variation in hair stable isotope values for nitrogen (δ 15N, A) and carbon (δ 13C, B) for a population of brown bears in Sweden 199–2020. Box plots depict the annual means, quantiles, and outliers, while colored points depict the observed values by demographic class.
There was strong support in the data that δ 13C values were lower in years with greater bilberry production (\({\widehat{\beta}}_{\left(\ln\left(\text{Bilberry}\right)\right)}=-0.21,\ 95\%\ CI=-0.30\ to-0.12\)) and greater numbers of observed moose calves (\({\widehat{\beta}}_{\left(\text{MooseCalves}\right)}=\ -0.25,\ 95\%\ CI=-0.35\ to-0.14\)). animal foods (i.e., moose and ants) had the highestδ 13C values, crowberry and lingonberry had median δ 13C values, and bilberry had the lowestδ 13C value. In years with high bilberry production, brown bear δ 13C values were more similar to bilberry, which should indicate a diet higher in bilberry, even when moose calf numbers were high.