Every autumn, the European nightjar leaves its breeding grounds in Europe and flies thousands of miles to southern Africa — then turns around and does it again in spring. A journey like that seems to demand wings built for one thing above all else: efficient, long-haul travel.
So when researchers at Lund University put the nightjar in a wind tunnel, they expected to find a bird finely tuned for the road. What they found instead made them look twice.
A migrant built for two very different jobs
The European nightjar lives a double life. By night, it hunts insects on the wing — hovering, banking, and pivoting through the dark with slow, precise movements. By season, it crosses entire continents between Europe and southern Africa. These two roles demand very different things from the same pair of wings.
Slow, agile hunting calls for broad, maneuverable wings that can generate lift at near-stall speeds. Long-distance migration rewards something leaner. Trying to do both well with one set of wings creates an inherent design tension — and that tension is exactly what the Lund University researchers set out to understand.
Inside the wind tunnel: how the nightjar actually flies
To study how the nightjar resolves that conflict, researchers placed the birds in a wind tunnel, recorded wing movements across a range of speeds, and mapped the airflow patterns left behind. That technique reveals how efficiently a wing is doing its job.
The results showed a clear trade-off. The nightjar’s broad wing tips — useful for maneuvering at slow speeds during hunting — become a liability at higher speeds, generating lift less efficiently when the bird is flying faster. Lift is the aerodynamic force that keeps a bird airborne, and losing efficiency there matters across a long migration.
The finding challenges a reasonable assumption: that a bird traveling thousands of miles must have wings tuned primarily for efficient cruising.
“This runs counter to the intuitive image of a long-distance migrant as a perfectly optimized flying machine,” said Christoffer Johansson, associate professor at Lund University. “Instead, the nightjar’s wings appear to be a compromise between several different demands.”
The upstroke surprise: thrust where birds don’t usually find it
In most birds, the upstroke — the phase where the wing rises back up after each downbeat — is relatively passive. It may contribute some lift, but forward thrust is typically the downstroke’s job.
The nightjar doesn’t follow that pattern. The Lund University team found it actively generates thrust during the upstroke, pushing itself forward even as its wings move upward. That’s a meaningful departure from the standard bird playbook, and it appears tied to the nightjar’s limited ability to fold its wings tightly during that phase. Rather than tucking in to reduce drag, the bird seems to turn that restricted movement into an aerodynamic advantage.
“What’s interesting is that the same type of aerodynamic solution seems to appear in quite different animals,” Johansson said. “This suggests that the upstroke does not have to be merely a passive or lift-generating part of the wingbeat. It can be actively used to generate thrust when the wings cannot be folded very much.” That places the nightjar alongside bats and insects — and raises the possibility of convergent evolution arriving at the same solution independently.
What evolution reveals when one body part serves many masters
The nightjar’s wings tell a broader story about how evolution actually works. It doesn’t always produce specialists. Sometimes it produces compromises — functional enough at several things, perfect at none.
For the nightjar, that means a wing shape supporting continental migration while preserving low-speed agility needed to catch insects in the dark. Neither function wins outright. Both get enough. For biologists studying how competing selection pressures shape anatomy, that outcome matters: when the same structure must serve multiple purposes, trade-offs tend to follow, and finding them helps explain why animals look and move the way they do.
Lessons for drones and flapping-wing aircraft
The nightjar’s aerodynamic quirks aren’t just interesting to biologists. Engineers designing flapping-wing drones face a structurally similar problem — how do you build a wing that moves efficiently through different phases of each beat, especially when folding is mechanically restricted?
The upstroke thrust finding could point toward new design strategies for robotic fliers that need to generate force throughout the full wingbeat cycle rather than relying on the downstroke alone. “This knowledge may also inspire the development of new types of flapping aircraft,” Johansson said. The team now plans to investigate whether this upstroke mechanism appears in other birds and flying animals — determining which principles are unique to the nightjar and which might be more widespread.
More information is available here: L. Christoffer Johansson, Gabriel Norevik, Sonja Friman, Anders Hedenström. Nightjars trade off cruising speed efficiency for hovering capabilities and link upstroke thrust production with restricted wing folding. PLOS Biology, 2026; 24 (9): e3004023 DOI: 10.1371/journal.pbio.3004023
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