The swift (Apus apus), a small migratory bird of the Apodidae family, seems to be shaped by air and air. In flight it resembles a crescent moon, with a small head and tail that accompany the curvature of the wings. It has been known for some time that this bird can fly for days without stopping, never resting anywhere, but now a search finds that it can even spend 10 months in flight without ever settling.

It falls to the ground only when it has to build its nest, to deposit and hatch its eggs, because in flight it can also mate.

Image A swift on the ground: it is not easy to surprise him like this. |

At rest for a few moments. Anders Hedenstrom, biologist at the University of Lund (Sweden), conducted his study on the swift (see Current Biology, in English) with the help of detectors which, in 1.1 grams, include accelerometer and light sensor, for determine the position of the bird by day and by night.

In this way, 19 swifts were "followed" between 2014 and 2015, who spent the winter in West Africa and the summer in Europe.

Three of them have never landed, literally; the others fell on rare occasions, during the night, and only for a few minutes. The fact is that on average the birds remained in flight for 99 percent of the time, with the exception of the nesting period.

The mystery of sleep. The records made it possible to verify that throughout the year, especially at dusk, birds can climb up to over 2 km in altitude. Hedenstrom believes that when they reach these heights, they rest until they fall asleep while they continue flying like gliders. It is difficult to explain how swifts and other birds manage to sleep in flight: they should perhaps resort to brain detectors on their heads, but those available today weigh too much.