A BIRD-LIKE, shape-shifting robot built to mimic the way the common swift alters its wing geometry during flight could slip in unnoticed among a flock of real birds.

Equipped with twin cameras that beam back three-dimensional video, it could allow people to fly virtually with real birds and gain a first glimpse of how the swift flies in its natural environment. "They are really agile and to study them you have really got to fly close to them - and look like them," says David Lentink of Wageningen University in the Netherlands. "Some birds will attack any model aircraft that comes close," he adds.

In April, Lentink and his colleagues at Wageningen University and the Technical University of Delft, also in the Netherlands, analysed the swift's hyper-efficient flying technique (Nature, vol 446, p 1082). They observed swifts flying in wind tunnels and used high-speed video to work out ...