This article has been reviewed according to Science X's editorial process and policies. Editors have highlighted the following attributes while ensuring the content's credibility: The European nightjar (Caprimulgus europaeus) is a nocturnal migratory bird that travels between Europe and southern Africa each year. However, its wings are not only used for long-distance journeys.
When hunting insects, the nightjar must be able to slow down, turn sharply and fly at low speeds. Researchers at Lund University have now shown how this trade-off is reflected in the bird's flight mechanics. The study is published in the journal PLOS Biology.
Using a wind tunnel, the researchers observed nightjars flying at different speeds and measured the airflow behind them. The results show that the bird's broad wingtips, which are likely advantageous for slow flight, come at a cost. As the bird increases speed, lift production becomes less efficient.
"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.
The researchers also made another unexpected discovery. The nightjar generates thrust even when its wings move upward. Such an active upstroke has previously been associated mainly with bats and insects rather than birds.
"What's interesting is that the same type of aerodynamic solution seems to appear in quite different animals. 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," says Johansson.
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