Chemical cues play an important role in mammalian communication, often reflecting an individual’s physiological state. Non-invasive sampling of such informative cues holds great potential for wildlife monitoring. Endangered apex predators such as big cats are elusive and challenging to monitor. While existing monitoring techniques estimate numbers or densities, they often fail to provide crucial demographic and physiological information. We adapted a headspace solid-phase field sampling technique adapted for sampling volatiles from urine and faeces of captive Bengal tigers and Indian leopards of known age and sex, and from urine of identified wild Bengal tigers of known age, sex, and reproductive status. Volatiles extracted from these samples were analysed using Thermal Desorption- Gas Chromatography-Mass Spectrometry. The random forest algorithm was used to identify compounds that might be cues for species, age, sex, and reproductive state.

Species classification accuracy was consistently high with both urine (0.79+0.009) and scat (0.75+0.029) volatiles. Classification accuracy of urine volatiles was high for females and young individuals in leopards and tigers, but lower for males and old individuals. Scat volatiles performed better across groups. We also identified putative chemical markers for epilepsy and reproductive state in tigers. This study presents the first chemical characterization of tiger and leopard scats and the first sampling of tiger odours from the wild. Our simple and cost-effective method of sampling tiger and leopard odours offers a novel method of chemical fingerprinting to monitor populations in situ. Importantly, this sampling method and analytical pipeline is broadly applicable to other mammalian species for conservation and ecological studies.