Secrets of Cross-Country Flight: How Birds Master Thermal Currents for Long-Distance Travel
In a study published in iScience, the scientists collected and analyzed a comprehensive GPS dataset of thermal soaring birds, validating long-standing aerodynamic theories. By integrating aerodynamic principles with high-frequency GPS tracking data from over a hundred individuals across 12 species—including vultures, eagles, and storks—, the team discovered universal strategies that birds use to maximize their efficiency during long-distance flights.
“We found that birds with higher wing loading—those that are heavier relative to their wing size—typically fly faster, while lighter birds can exploit weaker thermals and adapt to varying thermal strength more efficiently,” says first author Göksel Keskin from the Department of Biological Physics at ELTE Eötvös Loránd University in Hungary. “These findings not only confirm aerodynamic theories but also reveal how different species adapt their flight strategies”.
Linking Gliding Speed to Thermal Strength
One of the study’s key discoveries is that birds dynamically adjust their gliding speed between thermals based on updraft strength. This adaptive behavior allows birds to cover more distances with less energy, a crucial advantage for long-distance migration and foraging.
“This balance between speed and energy conservation is fundamental to their survival,” explains co-author Olivier Duriez from the University of Montpellier. “Different species have evolved unique ways to achieve it, depending on their ecological needs.”
The researchers identified a range of strategies that species use to adapt to varying thermal strength. Some species in the study precisely tune their gliding speed to match thermal strength, maximizing efficiency. In contrast, at the other end of the behavioral spectrum, White Storks maintain at a relatively constant speed regardless of thermal strength, likely to facilitate coordinated travel as a flock. Their aerodynamic properties are optimized for soaring, allowing them to lose minimal altitude during gliding.
“These differences highlight how species-specific movement strategies are shaped by ecological and social factors,” notes co-author Andrea Flack from the Max Planck Institute of Animal Behavior.
The Role of Wing Loading
A major finding of the study is that birds with lower wing loading demonstrate greater adaptivity to thermal strength. Birds like the Lesser Kestrel, which have lighter bodies relative to their wing size, can circle tighter and exploit weaker thermals more effectively.
“Wing loading is a critical factor in how birds interact with thermals,” says senior author Máté Nagy, head of the MTA-ELTE Lendület Collective Behaviour Research Group. “Understanding this relationship enables us to better predict how different species will respond to changing environmental conditions, such as variations in thermal strength.”
Lessons for Technology
The insights from this study extend beyond biology, offering inspiration for the development of autonomous gliders and drones. By understanding how birds adjust their flight speed and turning radius based on thermal strength, researchers can design robotic systems that mimic these energy-efficient strategies.
“Birds have evolved to master the art of soaring over millions of years,” says co-author Pedro Lacerda from ELTE Eötvös Loránd University. “By uncovering the rules they follow, we can apply these principles to create smarter, more efficient flying machines for tasks like environmental monitoring or search-and-rescue missions.”
Original publication: Title: Adaptive cross-country optimisation strategies in thermal soaring birds. Göksel Keskin, Olivier Duriez, Pedro Lacerda, Andrea Flack, Máté Nagy. iScience 112090. DOI: https://doi.org/10.1016/j.isci.2025.112090
Photo: Keskin et al. 1, 2