The study using new technology developed by researchers from the University of Oxford was undertaken in the Bubye Valley Conservancy, a privately-owned wildlife sanctuary in the arid south-west of the country that is home to around 500 lions and other members of the Big Five.
The researchers mapped the locations and climatic conditions behind 990 roars — and found water and lack of wind were among factors that played a big role.
“Water has been shown in previous studies to be a key resource for lions. It supports prey. It can also be used for breeding sites,” said Matthew Wijers, a post-doctoral researcher at Oxford’s Wildlife Conservation Research Unit and lead author of the study published in the current edition of the journal Animal Behaviour.
“I personally encountered many lions giving birth to cubs along the river lines. So I think those features in particular are high-value resources that they try and protect.”
Discovering how often lions roar near water — where that water is within their home range — still came as a surprise.
“It makes sense in theory, but to actually see that shown in the data is interesting,” Wijers told RFI.
New way to detect roars
To gather the data the scientists had to think out of the box. Audio recording devices are heavy on batteries, and run flat within a few days. So the research team used custom-built accelerometer biologgers attached to collars fitted on the lions that were able to gather data over a much longer period. When lions roar they move their heads and necks, and those movements are captured on the biologgers.
The research team then developed a computer algorithm that automatically matched the movement data with roars, and the precise locations of the lions when they roared were pinpointed by GPS devices also fitted to the animals’ collars.
“I’m really glad it worked because it does open up this new way of detecting roars,” Wijers said.
Nine-hundred and ninety roars later, he and his team made several important findings.
One was that lion roars were made more frequently in the early evening, continued throughout the night and peaked shortly before dawn. Another was that lions avoided roaring outside their home ranges within the 850,000-acre conservancy.
“This avoidance behaviour can be attributed to the increased costs of engaging in conflict with other territorial males and the reduced benefits of vocalizing away from owned resources,” the researchers wrote in their paper.
It was also found that lions like to roar when air temperatures are low, humidity high and there’s not much wind.
Populations in decline
Cool, humid air allows sound to travel further than warm, dry air, while excessive wind “masks” the frequency bands that roars travel in, Wijers explained.
“High winds create a lot of noise so in choosing to avoid those periods they obviously recognise there’s not a lot of benefit in doing so,” he said.
“The atmospheric and weather conditions mentioned in the report definitely does play a role in the acoustics of roaring,” said Norman Monks, head of the African Lion and Environmental Research Trust, a conservation group based in Zimbabwe’s resort town of Victoria Falls.
Monks, who was not part of the study, told RFI: “I think that this study is very sound and interesting and confirms scientifically and statistically what many of us bush scientists have suspected from casual observation.”
Knowing where and when lions are likely to roar will help researchers to know where to set up recording devices, known as passive acoustic monitoring equipment, on trees. This is a less intrusive way of gathering information on lions than putting collars on them.
Africa’s lion populations have declined dramatically over the last century mainly due to habitat loss, and from conflict with humans whose livestock they sometimes prey on.
Keeping tabs on their numbers and their movements plays a key part in conserving these iconic animals.