Scientists have discovered a new type of lion roar — the intermediate roar — which is shorter and lower-pitched than the animal's iconic, full-throated roar.
The researchers found that these intermediate roars always follow full-throated roars. The discovery reveals that lion vocalizations are more complex than previously thought, said study lead author Jonathan Growcott, a doctoral student in mathematics and statistics at the University of Exeter in the U.K.
The discovery, published Friday (Nov. 21) in the journal Ecology and Evolution, challenges the long-held belief that there is only one kind of lion roar, and it could help researchers estimate lion population sizes more accurately, he said.
Lions roar to communicate with their pride and establish their territory. Previous research has indicated that lions' full-throated roars are unique, individually identifiable signatures that contain information about an animal's sex, age and other characteristics. This suggests sound recordings can help scientists count the number of lions in a landscape and thus make population density estimates, Growcott said.
For the study, the researchers deployed 50 custom-built microphones in Tanzania's Nyerere National Park and attached acoustic sensors to collars on five lions in Zimbabwe's Bubye Valley Conservancy area. In total, the team recorded 3,149 African lion (Panthera leo) vocalizations.
The team then used artificial intelligence (AI) to analyse the sounds, which revealed the intermediate roar.
Without AI, understanding full-throated roars and identifying lions based on their vocalizations has always been subjective, Growcott said. Lions also make other sounds — including grunts, snarls, chuffs, moans and mews — but only full-throated roars have been shown to hold identifiable signatures, so it is important to identify these roars correctly and extract as much information as possible from them.
The researchers' AI model enabled them to classify lion vocalization types with over 95% accuracy, largely removing the bias that is introduced when researchers try to characterize lion calls manually. This approach also made it easier to identify individual lions based on their full-throated roars, and highlighted the previously unknown intermediate roar — knowledge of which will help researchers to isolate full-throated roars in the future.
"This new method which proves that intermediary roars exist and are different to the full-throated roar is an important first step for ensuring consistency in selecting full-throated roars," Growcott said.
There are only about 23,000 African lions left in the wild, making the species vulnerable to extinction, according to the IUCN Red List. Traditional methods to estimate lion population sizes include camera traps and spoor surveys, but these require large resources and may be less accurate than acoustic surveys.
"I hope that using data-driven predicted full-throated roars will lead to more accurate acoustic population density estimates which can better inform the pressing needs of conservation," Growcott said.
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