Since the ‘60s, ornithologists and birdwatchers have speculated about the long-distance prowess of common Swifts (Apus apus), but no one couldn’t imagine that the swifts annually spend almost 10 months in flight. It is very-well known that the swift is adapted to an aerial lifestyle, in which both food and nest material are captured in the air.

The news is that swifts can stay airborne for their entire non-breeding period, including their migration into sub-Saharan Africa. Scientists at the Lund University (Sweden) have equipped Common Swifts with a micro data logger with an accelerometer to record flight activity for two years, and with a light-level sensor for geolocation in the second year only. The measurements have demonstrated that swifts are airborne for >99% of the time during their 10-month non-breeding period: most birds have occasional flight inactivity, while some individuals have never settled. Flight activity seems lower during the day-time than during the night-time, likely because swifts tend to have prolonged gliding episodes during the day-time, when they are soaring in thermals.

The twilight ascents have been observed throughout the year, and not only in the summer, as previously reported. These results have important implications in understanding physiological adaptations of swifts to make possible the prolonged periods of flight, including the capability to sleep while airborne.