The unique roars of leopards

Leopards are masters of stealth, making them challenging to study in the wilderness. But a groundbreaking new study has found a new way to identify these elusive cats: not by sight, but by sound. By analysing their unique roars, researchers have unlocked an innovative, non-invasive method to track and conserve leopards. 

The leopard is one of the most sought-after Big 5 animals to view on an African safari. You will not find leopards in large numbers, as they are solitary. These masters of stealth are also more active at night, making them even more challenging to find.

This is a challenge not only for tourists but also for counting leopards and for the owners of land where leopards are present. A leopard’s furtiveness makes it nearly impossible for humans to gain insight into the number of individuals present in a local population. At the same time, leopard numbers are declining, and they are listed as vulnerable on the IUCN Red List of Threatened Species. How can we preserve a species that is difficult to find?

Camera traps are possibly one of the most important tools in studying leopards. Just like humans have unique fingerprints, leopards all have unique spot patterns, and visuals from camera traps allow us to identify individual leopards. However, a new study published in Remote Sensing in Ecology and Conservation offers a novel approach to identifying leopards: listening to their voices.

Researchers studying leopard vocalisation have found that every individual cat animal has a unique voice.

The study, which aimed to determine whether it was possible to identify individual leopards by their unique calls, took place in Nyerere National Park in Tanzania over 62 days. This is the firs, large-scale (~450km²) study of large African carnivores that pairs passive acoustic monitoring and camera trapping. Analysing photographic data, researchers identified 42 individual leopards present in the study area based on their distinctive rosette patterns. They then correlated these visual identifications with concurrent audio recordings, focusing on the leopards’ characteristic sawing roars.

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The team deployed 64 stations across the approximately 450km² area, strategically placing paired camera traps and custom-built autonomous recording units (CARACALs). The CARACALs recorded audio continually, while camera traps captured photographic evidence. Researchers then identified individual leopards by looking at their distinctive rosette patterns in the camera trap images and extracted their roaring bouts in the concurrent audio. Using this technique, the researchers identified individual leopards with a 93% success rate.

According to Jonathan Growcott, a PhD student at the University of Exeter in England and the study’s primary author, the idea to use bioacoustics stemmed from anecdotal evidence suggesting individual leopards have distinct roars. “Combined with the fact that other large carnivores such as lions, wild dogs, and spotted hyenas all have unique vocalisations, it made sense that this potentially also transferred across to leopards.”

Researchers found that leopards can actually be quite vocal – although it is easy to assume otherwise, with infrequent encounters leading to this misconception. Limited pre-existing research on leopard vocalisations highlights the significance of this study.

A project of this scale does not come without its challenges. Apart from the massive team effort involving multiple organisations, conditions in the reserve at the time of the study also made the research process difficult. “We dealt with flooding and incredibly difficult black cotton soil, which made roads impassable. We did not let this stop us, however. Instead, we embarked on foot to recover all of our data,” explains Growcott. He explains that, when working in a wild environment, animals could also cause problems. “On one occasion, a lion decided to investigate our acoustic unit, which was screwed into a tree. This individual promptly spent a good 20 minutes chomping and chewing at it. Remarkably, the SD card contained within the unit survived. I have some incredible audio of a lion, up close and personal.”

When asked if the results were at all what the team expected, Growcott said the accuracy of the results was quite exciting, especially with the basic methods used. “The methodology used is quite a basic principle in computer science and has been used in human-speech recognition algorithms for quite some time. So, to be able to achieve this kind of result without the need for more complex AI is encouraging.”

Landowners and reserves with leopards can deploy the same techniques, though there are some cost implications initially. To conduct a dual-technology survey from scratch would rely on a significant initial investment to purchase all the necessary equipment. Growcott says the costs would be split across an extended period, however, so monitoring can occur for multiple years, making the initial investment worthwhile.

The study’s findings hold significant implications for leopard conservation. Identifying individual leopards through their roars provides a powerful new non-invasive tool for monitoring populations, estimating densities, and tracking individual movements. This method overcomes many of the limitations associated with traditional methods such as collaring, offering a more efficient and cost-effective approach to studying elusive species.

The project was made possible due to collaboration between the University of Exeter, the Wildlife Conservation Unit at the University of Oxford, the Frankfurt Zoological Society, the Tanzania Wildlife Institute for Research, Lion Landscapes, and the Tanzania National Parks Authority.

Reference

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