Identifying populations of wild, free-roaming animals is a difficult and time-consuming task. Confirming this visually is also very difficult for species that live unusual lives, such as big cats that are independent, or may be nocturnal, or live in places that are difficult to reach. Because of the need to protect and conserve species like leopards, scientists have developed a cheap and highly accurate way to identify leopards using their sounds.
At Nyerere National Zoo, in southern Tanzania, 64 camera-trapping stations were used to capture images of leopards within the park. In addition to the camera traps, in 50 stations, independent recording units (CARACALs) were installed, each with four microphones to record the sounds of leopards. Records are made between 20 September and 20 November 2023.
With a camera recording station and an audio recording station, the group can tell that the vocals are coming from different people.
Image credit: Jonathan Growcott
The team looked at the images that the camera traps had previously taken, to identify individual leopards. Once that was established, they proceeded to listen to the audio files recorded at the same time as the photos.
The leopard has an incredibly distinctive call, known as the “sawing roar”. The team was able to identify that the leopard’s roar had three stages, including the first stage and the last stage known as “ruffs”. The team included data in their analysis when the leopard roared 10 minutes after the photo was taken.
“The discovery that cheetahs roar in a unique way is an important but important finding that shows how little we know about the cheetah, and large carnivores in general,” said the lead author. Jonathan Growcott, a PhD student at the University of Exeter, said in a statement. at IFLScience.
In total the team was able to identify 42 different leopards from more than 191 images of leopards taken by camera traps. There were 23 times the leopard also roared within 10 minutes of being photographed, and a total of 14 different leopards were present. Due to some technical problems and exclusions from the analysis, the group ended up with seven leopards, 26 roars, and 217 human roars.
The researchers used the “fundamental frequency contour” of the second part of the leopard to recognize people by their voices alone. Using their modeling technique, they could identify individual roars with 93.1 percent accuracy.
In general, leopards have vocalizations that can be recorded and assigned to individuals as an inexpensive way to identify them with high accuracy. The team thinks this is the first example of leopards being found using autonomous recording units, and it shows that they have an increased range of detection.
When combined with other methods, the team thinks that audio recording can be a good tool for population estimation and provides a more promising and cheaper method than direct human observations.
“We hope it will allow leopards to be the target of complex science such as population studies and open the door to more work on what kind of vocalizations carnivores use as a tool, ” said Growcott.
“Importantly, our success in using different types of technology can hopefully lead others to consider how to integrate different types of technology in their research, as the wealth of information we provide can push science first and help us understand the environment and places in a more general way.”
Paper published in Remote Sensing In Ecology and Conservation.
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