Laser ablation carbon stable isotope analysis of bear hair to reconstruct dietary timelines

Understanding fine-scale diet shifts in free-ranging wildlife remains challenging because high-resolution diet data are typically costly, invasive, or difficult to collect through time. Our objective was to determine whether δ¹³C laser ablation-combustion-isotope ratio mass spectrometry (LA-IRMS) of hair could be used to detect the timing and direction of known diet switches among isotopically distinct foods fed to American black bears (Ursus americanus). We measured spatially resolved δ¹³C values at ∼200-µm intervals along individual hairs from two captive bears fed controlled diets of corn, white-tailed deer, and trail mix. We converted tip-to-root positions along hairs to time using estimated hair growth rates of 0.72 ± 0.34 mm/day for bear 1 and 0.55 ± 0.17 mm/day for bear 2. We found that changes in hair δ¹³C were as expected, corresponding closely with known diet switches. Across both trials and bears, δ¹³C increased during corn feeding and declined during deer and trail-mix treatments. The isotopic profiles for bears in this study provide proof of concept that δ¹³C LA-IRMS can detect multi-day diet switches from a single hair when the foods are isotopically distinct.