Tigers and leopards rarely announce themselves in forest. They move silently through dense vegetation, often avoiding human contact for years. Yet these elusive predators constantly leave behind messages for one another. Every spray of urine on a tree trunk and every scat deposited along a forest trail carries a chemical signature that tells a story about that animal.
Now, researchers from the National Centre for Biological Sciences (NCBS), part of the Tata Institute of Fundamental Research under the Department of Atomic Energy, have developed a novel way to read those messages. Using advanced chemical ecology techniques, they have shown that the scent compounds present in tiger and leopard urine and scat can reveal the species, age, sex and even reproductive status of the animal. The breakthrough offers wildlife managers a powerful new non-invasive tool to monitor India’s two most iconic big cats.
The study, recently published in the Journal of Chemical Ecology, represents the first successful sampling of scent signatures from individually identified wild tigers. It combines cutting edge analytical chemistry with wildlife conservation and opens up a new frontier in animal monitoring known as volatilomics, the study of volatile organic compounds released by living organisms. The research was supported by a grant from the National Geographic Society.
Chemical ecologist BV Aditi Prasad who spent months collecting samples from tigers and leopards. Photo Credit: NCBS
At the heart of the work is a young researcher, BV Aditi Prasad, who spent months collecting samples from captive tigers and leopards in zoos across Bengaluru, Ahmedabad and Vadodara, as well as wild tigers in Rajasthan’s Ranthambore Tiger Reserve. The work required painstaking effort. Tigers had to be observed until they sprayed urine while marking territory. Once the animal moved away, samples were collected from the exact location before the scent evaporated.
 “Tigers and leopards are elusive, solitary, and endangered, making them notoriously difficult to monitor in the wild,” Aditi said. “Current monitoring methods can estimate how many big cats are out there, but they fall short on demographic and physiological details such as age, sex and reproductive status. The advantage of our method is its simplicity. Samples are easy to collect and analysis is easier than genetic testing, making it practical for field teams.”
The science is rooted in the behaviour of big cats. Tigers and leopards are intensely territorial animals. They communicate with rivals and potential mates by leaving scent marks throughout their home ranges.
The urine sprays are postcards left at prime locations warning rivals of their presence. Urine and scat contain volatile organic compounds that act as chemical signals. Other animals can detect these molecules and extract information about the individual’s identity and status.
Sampurna, BV Aditi Prasad and Uma Ramakrishna, the researchers who tracked the elusive tigers in Ranthambore National Park, Rajasthan. Photo Credit: NCBS
The research team wanted to know if modern analytical instruments and machine learning algorithms could decode the same information hidden within these odours. Using ultra-sensitive thermal desorption gas chromatography mass spectrometry, they analysed hundreds of samples and identified several chemical compounds that reliably distinguished tigers from leopards. They also discovered chemical combinations that could indicate whether an animal was male or female and whether it was young or old.
Most remarkably, the team identified a chemical marker associated with reproduction. The compound 2 nonanol was found at significantly higher levels in pregnant and lactating wild tigresses than in non-reproductive females. This means that conservationists may one day be able to determine breeding success simply by analysing scent marks left in the forest.
For India, which now holds the world’s largest tiger population, such advances come at a critical time. The country’s tiger monitoring programme has evolved dramatically over the past few decades. During much of the twentieth century, tiger numbers were estimated through pugmark tracking. Forest officials identified footprints and attempted to distinguish individuals using the size and shape of paw impressions. Although innovative for its time, the method was often criticised because tracks could be misidentified and estimates were difficult to verify.
The transformation came with camera trapping and statistical capture-recapture techniques. Motion triggered cameras provided photographic evidence of individual animals, whose stripe patterns serve as unique identifiers. Combined with habitat surveys and occupancy modelling, India developed one of the world’s most sophisticated wildlife census systems.
The results have been dramatic. India’s tiger population, which stood at 1,411 in the 2006 All India Tiger Estimation, increased to 1,706 in 2010, 2,226 in 2014, 2,967 in 2018 and 3,167 in 2022 according to official national tiger assessments. These advances have helped establish India as the global stronghold for tigers despite have a burgeoning human population now reaching nearly 1.4 billion people.
Yet even modern camera trap surveys have limitations. Cameras can identify individuals but often struggle to accurately assess age, health, reproductive condition or physiological status. This is where chemical ecology may add an important new layer of information. By combining camera trap images, DNA fingerprinting from scat samples and chemical signatures from urine and faeces, wildlife biologists could potentially build a far richer picture of a tiger population than any single technique can provide.
The NCBS team believes scent chemistry could complement existing monitoring systems rather than replace them. The researchers found that odour compounds can persist for hours and sometimes days after an animal has moved away, allowing sampling even when the tiger itself is nowhere in sight.
Supervising author Shannon Olsson noted that chemical analysis has long been used in medicine, nutrition and forensic science, but its application in wildlife conservation is only beginning. According to the researchers, the technique may eventually help managers monitor population health, reproductive success and even detect disease in free ranging animals.
The study provided an intriguing glimpse of this possibility. During the research, the scientists sampled a captive tiger undergoing treatment for epilepsy. The animal’s scat showed elevated levels of dimethyl tetrasulphide. While the observation came from only a single animal and is far from conclusive, it suggests that scent chemistry may someday offer clues about disease and health complications.
For Prof Uma Ramakrishnan, one of India’s most respected wildlife geneticists and a senior author of the study, the significance extends beyond tigers and leopards.
“We are lucky to share our planet with many amazing animals. Yet we know so little about them. The novel chemical ecology tools showcased here, when integrated with other approaches, are sure to help us understand and conserve these amazing animals better,” she said.
The implications stretch far beyond India’s forests. The sampling method developed at NCBS is inexpensive, non-invasive and adaptable to other species. Similar approaches could eventually be used for wolves, bears, wild dogs, snow leopards and many other threatened mammals.
For decades, wildlife science has relied on footprints, photographs to track elusive animals. The NCBS study suggests that another source of information has been waiting in plain sight all along. Every scent mark left by a tiger or leopard is not merely a territorial declaration. It is a chemical dossier packed with information. Thanks to a Department of Atomic Energy laboratory and a determined young researcher willing to follow tigers through forests and zoos alike, scientists are finally learning how to read it. Now one can literally smell tigers.
