Christoffer Johansson watched a European nightjar hover like a moth in the soft light of a wind tunnel at Lund University. The bird’s wings beat the air with quiet precision, moving so slowly at times it seemed to hang in place. But this wasn’t just about hunting insects in the dark—it was about understanding a deeper truth: nature rarely builds perfection, but instead finds balance.
Every year, the European nightjar migrates from Europe to southern Africa, a journey of thousands of kilometers. To do this, you’d expect it to have wings built for speed and efficiency. But it also needs to fly slowly, twist through trees, and snatch insects midair at night. How can one wing do both? That’s what Johansson and his team set out to answer.
Using a wind tunnel, the researchers filmed nightjars flying at different speeds and measured the airflow behind their wings. They found that the birds have broad wingtips—ideal for generating lift during slow, agile flight. But there’s a catch. When the birds fly faster, those same wingtips make lift production less efficient. In other words, the nightjar’s wings are not perfectly tuned for long-distance travel. They’re a compromise.
"This runs counter to the intuitive image of a long-distance migrant as a perfectly optimized flying machine," says Johansson. "Instead, the nightjar's wings appear to be a compromise between several different demands."
Even more surprising, the team discovered that nightjars generate thrust on the upstroke—the part of the wingbeat when most birds simply recover position. By keeping their wings extended and angled just right, nightjars push air backward even as their wings rise. This kind of active upstroke is rare in birds and was thought to be mostly seen in bats and insects.
The finding suggests that when wings can’t fold tightly—like the nightjar’s long, stiff feathers—evolution finds another way. The upstroke becomes a second chance to move forward.
This balance between slow flight and long migration isn’t just fascinating biology. It could inspire new designs in robotics. Engineers building flapping drones face similar limits: how to make a wing that’s good at hovering, turning, and traveling far. The nightjar’s solution—compromise with clever aerodynamics—might point the way.
Now, the team wants to see how common this flight style is in other birds. If more species use their upstroke to thrust, it could rewrite how we think about bird flight. And if engineers take note, our next generation of flying machines might move more like moths, bats, and nightjars than we ever expected.