For the vast majority of land creatures, the ground or branches are an essential sanctuary for rest. However, the common swift (Apus apus) defies the conventional laws of the animal kingdom: it is capable of spending up to ten entire months in the air without landing a single time on solid ground.
Although ornithologists had suspected this behavior since the 1950s, it was not until 2016 that a team from Lund University (Sweden), led by biologist Anders Hedenström, proved it scientifically. Using tiny microaccelerometers attached to migratory specimens, they confirmed that several birds spent 99.5% of their migration without descending, and some did not touch any surface for more than 300 consecutive days.
This astonishing feat raises an immediate question: how do they satisfy their vital needs without landing?
- Feeding and hydrating on the wing: They catch thousands of insects in midair with a wide bill that acts like a net, and they drink by skimming the surface of lakes at full speed.
- Reproduction and preening: They are capable of copulating in mid-glide and keeping their plumage in perfect aerodynamic condition.
- The sleep enigma: To sleep, they ascend in spirals at dusk up to altitudes between 2,000 and 3,000 meters. They are believed to use unihemispheric sleep, shutting down half of their brain while the other half maintains controlled, alert flight.
Its scythe-shaped wings and streamlined body make the swift a nearly frictionless aerodynamic machine, touching solid ground only during the two months of the nesting season to incubate its young.
Source: Current Biology (Hedenström et al., 2016)
