Lund researchers find nightjars trade fast-flight efficiency for agile hunting
Wind-tunnel tests by Lund University researchers found that European nightjars’ broad wing tips help them fly slowly and manoeuvre while hunting, but make lift generation less efficient at higher speeds. The study, published in PLOS Biology, also found that nightjars generate forward thrust during the wing upstroke, a feature previously associated mainly with bats and insects.
Bottom line — The Lund team plans to test how widespread upstroke thrust is among birds and other flying animals.
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The European nightjar migrates between Europe and southern Africa, while also hunting insects at low speeds.
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PLOS Biology reports that the study found a double tip-vortex pattern at cruising speeds, linked to reduced span efficiency.
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The researchers studied three birds in a wind tunnel at speeds from 2.6 to 11 m/s, according to the study.
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The authors suggest limits on folding the wings during the upstroke may help explain the thrust generation.
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Lund University researchers say the findings could inform designs for flapping-wing aircraft.