- A new study tested whether the chemical compounds in tiger and leopard urine and scat can reveal information about the animals without capturing them.
- The chemical profiles could distinguish tigers from leopards with 79% accuracy using urine and 75% using scat, while older male tigers and leopards were harder to classify.
- Further research could improve its accuracy and potentially extend the method to other wildlife.
Camera trapping and genetic sampling are big cat monitoring techniques that can estimate population size, density and identify individuals. But they often provide limited information about an animal’s age, sex, reproductive status or health. A new study now suggests that the animal’s urine and scat could reveal more than its presence in a forest.
Researchers from the National Centre for Biological Sciences (NCBS), Ahmedabad University and the Danish Academy of Technical Sciences tested whether volatile organic compounds (VOCs) present in urine and scat could provide a non-invasive way of collecting information about Bengal tigers and Indian leopards.
“The goal was to see whether you could ‘read’ biologically meaningful information — species, age, sex, even reproductive state — directly from the odours the animals leave behind, without ever having to catch, dart, or physically handle the animal,” says B.V. Aditi Prasad, the corresponding author of the study and currently a postdoctoral fellow at the Max Planck Institute for Evolutionary Anthropology, Germany.
Testing the method
The researchers collected urine and scat from nine captive tigers and 15 captive leopards at three zoos — Bannerghatta Biological Park in Bengaluru, Kamala Nehru Zoological Park in Ahmedabad and Sayajibaug Zoo in Vadodara. The ages and sexes of the animals were known, allowing researchers to compare their chemical profiles with these characteristics.
They also collected 144 urine samples from 28 individually identified wild tigers in Rajasthan’s Ranthambore Tiger Reserve. “Ranthambore’s tigers are unusually well-monitored and individually identifiable, so samples could still be tied to a known individual, known age and sex, but now in a real, uncontrolled field setting. This lets you demonstrate that the sampling and analysis approach actually works as a practical field method, not just under lab-like zoo conditions,” explains Prasad. “Additionally, in the wild, we were able to sample tigers for reproductive status, such as lactation and pregnancy, since the zoo tigers were not reproducing.” The wild samples included 24 samples from four pregnant or lactating females.
In the zoos, urine and scat were collected from enclosure floors under the team’s supervision. In Ranthambore, researchers waited for identified tigers to leave before collecting the samples. They also collected samples of soil, grass, leaf litter, rocks and tree bark, as well as sterile cotton, as controls to distinguish animal odours from environmental and sampling-related contaminants.
The team collected the volatile compounds released from urine and scat using small silicone tubes and identified them using a laboratory technique called thermal desorption-gas chromatography-mass spectrometry. They then used Random Forest, a machine-learning method that looks for patterns in data, to see whether combinations of compounds could distinguish a tiger from a leopard, or a male from a female. They ran 100 Random Forest analyses to identify the most informative compounds and then tested the model’s accuracy using cross-validation.
What did they find?
The researchers say this is the first attempt to sample tiger odours in the wild and leopard odours non-invasively from individuals of known age and sex. The chemical profiles could distinguish tigers from leopards with about 79% accuracy using urine and 75% using scat.
They also found chemical differences associated with age and sex in both tigers and leopards, although classification accuracy varied between groups. In tiger urine, chemical profiles classified sex with about 55% accuracy and age with about 64% accuracy. Scat performed somewhat better for understanding the sex, at about 71%, and classified age with about 63% accuracy. However, older and male tigers were more often misclassified.
The method showed similar patterns in leopards. Depending on whether urine or scat was used, sex and age could be classified with roughly 55-65% accuracy. Older and male leopards were again harder to classify.
The wild tiger samples revealed a possible chemical cue linked to reproduction. A compound called nonanol was much more abundant in urine from pregnant and lactating females than in non-reproductive females. This suggests that urine could potentially provide a way to identify reproductive status without observing the animal directly.
The researchers also detected elevated levels of the VOC dimethyl tetrasulphide in the scat of a captive tiger being treated for epilepsy. But because this was only one animal, the finding cannot yet be used to diagnose disease. “As scientists, we found this more confirmation than surprise. But it’s striking that so much about a tiger — its sex, age, reproductive status, even signs of illness — can be read from a single whiff of urine or scat, without ever seeing the animal,” says Prasad.
The challenges ahead
This method is still at an early stage. The wild tiger sample came from just one population, and the researchers could not collect scat from individually identified wild tigers. All leopard samples and identified tiger scat samples came from captive animals.
The researchers also caution that VOC profiles can change with diet, weather, temperature and other environmental conditions. Scat contains dietary material and microbes, which can affect its chemical profile. Scat also degraded quickly in summer and could be washed away during the rainy season, the researchers found. Urine produced more consistent signals and could be sampled in both winter and summer.
“Sample sizes, especially for wild tigers, remain small; classification accuracy was lower for males and older individuals,” explains Prasad. “But despite differences in diet, habitat and seasons between captive and wild individuals, we found consistent signals, which is encouraging for scaling up the method. Broader validation across habitats and larger wild datasets is still needed,” she elaborates.
This method also cannot replace camera traps. Tiger cubs generally do not mark territories, so they may not leave the urine signals needed for this type of monitoring. Camera traps can still detect them.
A new tool for conservation
If further research validates this method of sampling volatiles, odour analysis could give wildlife managers some information that existing monitoring methods often miss. It could help distinguish tiger and leopard signs, since their scats and scrape marks are not always visually distinct. “Detecting chemicals in urine and fecal matter has been widely used in nutrition, medicine, and forensics. Applying such techniques to conservation offers researchers and managers the opportunity to directly monitor individual statuses for population health and safety,” says Shannon B. Olsson, the supervising author, from the Danish Academy of Technical Sciences. Further research could improve its accuracy and potentially extend the method to other wildlife.
For now, the researchers view odour analysis as a complement to, rather than a replacement for, camera traps, genetics and other monitoring techniques. “The novel chemical ecology tools showcased here when integrated with other approaches are sure to help us understand, and conserve, these amazing animals better,” concludes Uma Ramakrishnan from the NCBS, and a co-author of the study.
Banner image: A tiger marks its scent by spraying urine on a tree in Kanha National Park. Image by David V. Raju via Wikimedia Commons (CC BY-SA 4.0).
Read more: As tigers spill beyond reserves, India rethinks conservation
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