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 (δtissue - δdiet). These values, called trophic discrimination factors (TDFs, denoted with ∆), 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 (δ(13)C values) and nitrogen (δ(15)N values).

Results: It was found that the only significant TDFs in this study were diet-hair, ∆(13)CHair, for snow leopards (5.97 ± 1.25‰) and tigers (6.45 ± 0.54‰), and diet-scat, ∆(15)NScat, in snow leopards (2.49 ± 1.30‰). The other mean isotope ratios were not significantly different from that of the premixed feline diet. The ∆(15)NHair 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.