If you've ever seen a pigeon encounter a sharply inclined tree branch or other steep obstacle, you've probably also seen it "flap run." Rather than fly over these barriers, pigeons—and most other birds—climb up them while fluttering their wings, a behavior scientists refer to as "wing-assisted incline running." To figure out why birds do this, researchers implanted sensors in the wing and primary flight muscles of three pigeons, and had them traverse steep inclines in the lab. Flap running was over 10 times more energy efficient than flying, the team reports online today in The Journal of Experimental Biology, creating just enough aerodynamic force to push the birds' bodies upward while also supporting some of their body weight. In addition to solving the mystery of flap running, the findings may shed light on the evolution of flight in the ancestors of birds, dinosaurs.
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*This item has been corrected. Flap running was over 10 times more efficient than flying, not 10% more energy efficient.