The development and use of stable isotope analysis of felids’ whiskers as a tool to study their feeding ecology
Stable isotope analysis (SIA) of whiskers has been used to identify temporal feeding habits, intra-population diet variation, as well as individual dietary specialisation of marine and terrestrial carnivores. However, the potential of the method to disclose such dietary information for large wild felids has been little explored. The accurate interpretation of stable isotope ratios along serially sampled whiskers is hampered by lack of information on species-specific whisker growth rates, whisker growth patterns and whisker-diet trophic discrimination factors (TDFs). Whisker growth rate and growth pattern informs on the time period encapsulated in the analysed segment of a whisker, while whisker-diet TDFs are required to make correct deductions of the prey species consumed by a predator. The aim of this study was to develop and evaluate the technique of using stable carbon and nitrogen isotope analysis of felid whiskers to quantify the diet of wild felids and in particular, to identify diet variation among individuals. To achieve this, lion Panthera leo and leopard Panthera pardus whisker growth rate and growth pattern, and lion whisker-diet TDFs were measured, using captive individuals held at the National Zoological Gardens, Pretoria. The viability and applicability of the technique was then explored on six free-ranging leopards in Phinda Private Game Reserve (hereafter Phinda), northern KwaZulu-Natal (KZN) whose diets have been intensively studied using traditional methods. Whisker growth rates and growth patterns were measured for four lions (three sub-adult females and one adult male) and an adult male leopard over 185 days using giraffe Giraffa camelopardalis meat as an endogenous biomarker to consecutively mark whiskers as they grew. The 13C-depleted, C3-derived giraffe meat with its characteristic isotopic signature could be discerned from the 13C-enriched diet of C4 grain-fed beef and chicken the felids were sustained on. Two whiskers were removed from each felid at the beginning of the experiment, and felids were fed the giraffe meat at four predetermined periods to mark the whiskers replacing the removed ones. The periods with low δ13C values, identified following serial sectioning of the regrown whiskers at 1 mm intervals (and stable isotope analysis of these sections), were then correlated to specific giraffe meat feeding bouts and hence growth periods. Knowledge of the duration between giraffe meat feeding bouts enabled the calculation of whisker growth rate and determination of growth pattern. δ13C and δ15N whisker-diet TDFs were estimated for five lions whose diet remained consistent over multiple years. Whiskers removed from four lions at the beginning of the whisker growth experiment, a whisker removed from a female lion as part of a pilot study a year before the experiment and the diet (chicken and beef) samples collected during the experiment were analysed for their isotopic ratios. These were used to calculate isotopic differences between lion whiskers and diet.