Effects of Lipid Extraction on δ13C and δ15N Values in Seabird Muscle, Liver and Feathers

Abstract We determined whether lipid extraction of seabird muscle, liver and feathers is required for δ13C and δ15N analysis, based on a study of Barau’s Petrels (Pterodroma baraui) and White-tailed Tropicbirds (Phaethon lepturus). Samples were analyzed for stable isotopes before and after lipid removal. Lipid-free muscle and liver were significantly enriched in 13C compared to those containing lipids (0.52‰ and 0.61‰ mean differences in δ13C respectively) implying that lipids should be extracted from these tissues to avoid effects of uncontrolled differential lipid content. However lipid extraction also slightly increased muscle δ15N values in tropicbirds. Researchers should thus run samples separately for δ13C and δ15N analysis, extracting lipids only in aliquots in which δ13C is measured, or apply arithmetic δ13C normalization methods on non lipid-extracted samples. Predictive models developed from our data, inferring δ13C values of lipid-extracted material from δ13C values and C:N ratios of non lipid-...