Discrimination factors of carbon and nitrogen stable isotopes from diet to hair and scat in captive tigers (Panthera tigris) and snow leopards (Uncia uncia)

RATIONALE: In order to use stable isotope ratio values obtained from wild animal tissues, we must accurately calculate the differences in isotope ratios between diet and consumer (delta(tissue) - delta(diet)). These values, called trophic discrimination factors (TDFs, denoted with Delta), are necessary for stable isotope ecology studies and are best calculated in controlled environments. METHODS: Scat, hair, and diet samples were collected from captive tigers (n = 8) and snow leopards (n = 10) at the Bronx Zoo. The isotope ratios of carbon and nitrogen, the two most commonly used in ecological studies, of the samples were measured by continuous-flow isotope ratio mass spectrometry. The trophic discrimination factors were calculated for both carbon (delta C-13 values) and nitrogen (delta N-15 values). RESULTS: It was found that the only significant TDFs in this study were diet-hair, Delta C-13(Hair), for snow leopards (5.97 +/- 1.25 parts per thousand) and tigers (6.45 +/- 0.54 parts per thousand), and diet-scat, Delta N-15(Scat), in snow leopards (2.49 +/- 1.30 parts per thousand). The othermean isotope ratios were not significantly different from that of the premixed feline diet. The Delta N-15(Hair) values for both species were unusually low, potentially due to the protein content and quality of the feline diet. CONCLUSIONS: The discrimination factors of the stable isotopes of carbon and nitrogen calculated in this study can be applied to ecological studies of wild, non-captive terrestrial mammals. The effect of protein quality in isotope discrimination is also worthy of further investigation to better understand variation in TDFs. Carnivore scat is shown to be a valuable material for isotopic analysis. Copyright (C) 2015 John Wiley & Sons, Ltd.