As regular CFZ-watchers will know, for some time Corinna has been doing a column for Animals & Men and a regular segment on On The Track... particularly about out-of-place birds and rare vagrants. There seem to be more and more bird stories from all over the world hitting the news these days so, to make room for them all - and to give them all equal and worthy coverage - she has set up this new blog to cover all things feathery and Fortean.

Monday 26 November 2018

Swifts ride air currents to catch a free lunch

November 19, 2018, The Company of Biologists
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.
But the unique footage was not collected with a conventional camera. Mounting a pair of angled mirrors either side of a camera, with a third mirror in front of the lens to collect the reflections from the wide-set mirrors, de Margerie was able to film a pair of simultaneous movies—each from a slightly different perspective—which he could then analyse to perfectly reconstruct individual swift motions in 3-D. "The current device is cumbersome," says de Margerie, admitting that it takes time to learn how to track the swifts' tortuous flight paths. "After some training, our undergraduate student Cécile Pichot was the most skilful at continuously following foraging swifts for relatively long flight times of up to 6 minutes," he says.

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