A bird that migrates thousands of miles has revealed a surprising secret about how wings work. Scientists have discovered that European nightjars sacrifice flight efficiency for agility and use an unexpected wingbeat technique previously associated mainly with bats and insects. The European nightjar (Caprimulgus europaeus) is a nighttime hunter that makes an extraordinary annual migration between Europe and southern Africa.
Yet the wings that carry it across vast distances must also perform a very different task: helping the bird catch insects while flying slowly and making sharp turns. Scientists at Lund University have discovered that these competing demands come with a surprising trade-off. Although the nightjar is built to handle long migrations, its wings are not perfectly optimized for efficient flight at higher speeds.
Why Nightjar Wings Sacrifice Efficiency for Agility To investigate how nightjars fly, researchers studied the birds in a wind tunnel, recording their movements at different speeds and measuring the patterns of airflow left behind their wings. The experiments revealed that the nightjar's broad wing tips, which likely help it maneuver during slow flight, become a disadvantage as the bird flies faster. At higher speeds, its wings generate lift less efficiently.
Lift is the aerodynamic force that helps keep a bird airborne. The findings challenge the assumption that birds traveling enormous distances must have wings optimized primarily for efficient long-distance flight. "This runs counter to the intuitive image of a long-distance migrant as a perfectly optimized flying machine.
Instead, the nightjar's wings appear to be a compromise between several different demands. The bird can fly slowly and maneuver while hunting, but the trade-off is reduced efficiency in lift generation at higher speeds," says Christoffer Johansson, associate professor at Lund University. Scientists Discover an Unexpected Wingbeat Trick The researchers also uncovered another surprising feature of the nightjar's flight.
Even as the bird raises its wings during the upward portion of each wingbeat, it continues to generate thrust, the force that helps propel it forward. This is unusual because such an active upward wing movement, known as an upstroke, has previously been linked mainly to the flight mechanics of bats and insects rather than birds. The discovery suggests that animals with very different evolutionary histories may have developed similar aerodynamic solutions to the challenges of flying.
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