To Understand How Birds Soar, a Scientist Looks to Paragliders

Like vultures, the aerial athletes rely on thermals to power their flight. But how do they find these invisible updrafts?
A fisheye view from above a paraglider, the earth looks remote but the sky is filled with gliders.
Hannah Williams’s research uses multiple cameras to record a paraglider’s airspace and their eye movements to see how they observe other competitors. Photo: Hannah Williams

Of the thousands of sports that humans have invented, paragliding may be the most birdlike. In its competitive form, racers fly in groups known as gaggles, suspended from parachutes and powered solely by columns of warm, rising air called thermals. It’s a method of flight that mimics the movements of vultures and other birds known as obligate soarers. 

For these birds, finding thermals is not a thrill but a daily necessity. Flapping their large wings burns a lot of energy, so instead they rely on the updrafts to efficiently seek out food, a mate, and a safe place to roost. But thermals are invisible, so how do the birds know where they are?

That question fascinates Hannah Williams, a movement ecologist at the University of Konstanz in Germany. Her research showed that, while a scattering of vultures across the sky may not look tightly coordinated like a flock of starlings, they still read one another’s behavior—a phenomenon called social eavesdropping—to locate thermals. Williams wanted to know more about what signs they look for, but she was unsure how to find out; what drives social interactions and decision making is notoriously hard to measure in wild animals. 

A breakthrough arrived when Williams saw paragliders riding thermals while she was camping in the Swiss Alps. Perhaps by studying how the adventure athletes watch one another in flight, she figured, she could learn which visual cues are most important for soaring vultures. “I need to get into the head of a paraglider and then I can see what the birds see,” she recalls thinking.

A breakthrough arrived when Williams saw paragliders riding thermals.

To collect data on how paragliders use social eavesdropping, Williams and her collaborators have begun monitoring paragliders during races—up to 150 competitors at a time. A subset of the pilots wear cameras mounted to helmets and glasses to track their eye movements while filming their airspace in 360 degrees. As the study continues, Williams hopes the recordings will yield new insights into how groups soar together. 

Already one clear pattern has emerged: The larger the gaggle, the better its members navigate from one invisible thermal to the next, and the lower their risk of grounding. Williams wants to know how many individuals are required to reap the energy-saving benefits of traveling in a group, which could provide lessons for bird conservation. “This way we can identify possible critical thresholds whereby a certain population size is needed to find thermals and find food,” she says.

Such insights could prove useful for wildlife managers working to conserve the 22 vulture species that, taken together, are considered the most threatened avian guild in the world. Shawn Farry, condor reintroduction program manager at the Peregrine Fund, has observed California Condors watching one another across great distances, a hint that social eavesdropping is important for North America’s most endangered raptor. Releasing hand-reared individuals into established flocks can make a big difference for their success, he says: “If there’s a bunch of other birds around for them to follow, the learning curve is much quicker for them.”

Aurélien Prudor/Wild Talks

Williams’s dataset, the most comprehensive ever collected on paragliding behavior, could also help her human research subjects unlock strategies to win more races and fly more safely. Paragliding coach Malin Lobb, a participant in the project, is especially interested in working with Williams to develop strategies for gaining altitude in thermals more efficiently, something he says top pilots excel at but can’t easily teach to others. “It’s groundbreaking from a paragliding point of view,” Lobb says. “It could also help us massively.”

The project has involved hundreds of pilots, a role that members of the British Paragliding Racing Academy have been happy to fill. Observing birds has always been important to the sport: An upward-spiraling vulture or hawk, or a flock of swifts feasting on aerial insects, reliably marks a thermal, Lobb says. (Species that soar opportunistically, rather than by necessity, tend to meander and are less helpful: “I definitely know you shouldn’t follow a seagull.”) “What’s fascinating is that we behave exactly like the vultures,” he says. Some racers and some birds, for instance, are more likely than others to take risks, such as venturing ahead of the group without assurance that another thermal awaits them.

Encouraged by the world-class paragliders she works with, Williams has taken to launching herself off of mountainsides and parachuting into the world she studies. “I was amazed, actually, just how many different decisions go through your head at one point—way more than what we’re modeling with the birds,” she says. Aloft, Williams has encountered vultures flying in close to check her out, apparently as interested in her as she is in them.

This story originally ran in the Spring 2024 issue as “Flight Lessons.” To receive our print magazine, become a member by making a donation today.