Swifts ride air currents to catch a free lunch

[PhysOrg]

Once an adult swift (Apus apus) leaves its breeding colony and takes to the air migrating south, it won't touch down again until returning home to nest 10 months later. "Common swifts are exceptional in their level of adaptation to aerial life," says Emmanuel de Margerie, a biologist from the CNRS (Centre National de la Recherche Scientifique) at the University of Rennes, France, adding, "Foraging, sleeping, preening and all other daily activities are performed in mid-air, day after day, week after week." So, when de Margerie decided to learn how the expert aviators manoeuvre in their aerial domain, he contacted biomechanist Tyson Hedrick from the University of North Carolina at Chapel Hill, USA, who snapped up the opportunity. "Their basic flight capabilities have been well studied in wind tunnel experiments," says Hedrick. However, birds in wind tunnels never share the sky with others or contend with unexpected gusts of wind. de Margerie had filmed swifts soaring and swerving while foraging to feed their chicks and the movies provided the ideal opportunity to find out how much exertion it takes to keep an acrobatic swift on the wing in real life. They publish their discovery that swifts essentially hitchhike on rising currents to make their flight costs almost zero in Journal of Experimental Biology.

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