Establishing chronologies from isotopic profiles in serially collected animal tissues: An example using tail hairs from African elephants

While the use of stable isotopes in wildlife ecological research is growing rapidly, development of methods to establish time-specific isotope data from continuously growing animal tissues are lacking. Using serially collected tail hairs from wild African elephants (Loxodonta africana), we develop and compare four techniques to collate temporal isotope chronologies from metabolically inert tissues for which formation/growth overlapped in time. The influence of variation in within hair growth rates and other sources of error in the presented techniques are explored and found to be inconsequential relative to the 5-day tissue sampling interval. Using a floating point regression approach, we find a high degree of correlation between independently derived isotope profiles from the same and different individuals in the study ecosystem. Remotely sensed Normalized Difference Vegetation Index (NDVI) data is compared with the isotope derived diet chronologies from five elephants developed independently. Diet shifts from browse to grass occurring at the onset of the wet season were highly synchronized, while early dry season diets varied across individuals. These methods are applicable across a variety of keratinous tissues and even teeth and, as demonstrated by our results, can be implemented using profiles from different individuals or relating profiles to environmental variation (seasonality). As such, the presented methods allow the establishment of high resolution temporal data on diet, movement, and climatic conditions experienced by an organism in many research settings.