How do birds navigate the skies when they encounter turbulence? A new study from Oxford University poses an answer to this question. Researchers gave a captive steppe eagle its own flight recorder backpack – a 75g black box incorporating GPS that also measured acceleration, rotation rate, and airspeed – and recorded it soaring over the Brecon Beacons in Wales.

An analysis of data from 45 flights revealed that in windy conditions the eagle would collapse its wings in response to particularly strong gusts rather than hold them out stiffly as an aircraft would. During these 'wing tucks', the bird's wings were briefly (for around 0.35 seconds) folded beneath its body so that it was effectively 'falling'. The results suggest that these 'wing tucks' may occur up to three times a minute in some conditions.

A number of theories have tried to explain why birds perform wing tucks but up until now no one had tested these conclusively.

'Our evidence suggests that wing-tucking (collapsing the wings) is a direct response to a substantial loss of lift that occurs when a bird flies through a pocket of atmospheric turbulence,' said report author Professor Graham Taylor of Oxford University's Department of Zoology. 'We think that, rather like the suspension on a car, birds use this technique to damp the potentially damaging jolting caused by turbulence. Whilst we won’t see large aircraft adopting collapsible wings this kind of technique could potentially be used to keep micro air vehicles aloft even in very windy conditions.'

Via Oxford University press release

Northern Harrier by Rich Engelbrecht