title: Discrimination factors of carbon and nitrogen stable isotopes from diet to hair and scat in captive tigers (Panthera tigris) and snow leopards (Uncia uncia).
abstract: BACKGROUND
  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.
authors.affiliation: Columbia University, Department of Ecology, Evolution, and Environmental Biology, 1200 Amsterdam Avenue, New York, NY, 10027, USA.|Sackler Institute for Comparative Genomics, American Museum of Natural History, Central Park West at 79th Street, New York, NY, 10024, USA.
authors.forename: Shaena
authors.initials: S
authors.lastname: Montanari
authors.affiliation: Columbia University, Department of Ecology, Evolution, and Environmental Biology, 1200 Amsterdam Avenue, New York, NY, 10027, USA.|Sackler Institute for Comparative Genomics, American Museum of Natural History, Central Park West at 79th Street, New York, NY, 10024, USA.
authors.forename: George
authors.initials: G
authors.lastname: Amato