Flying swifts
Markus Tallroth

These frequent-flying swifts stay aloft for 10 months a year

With their aerodynamic form and sharp angles, common swifts (Apus apus) look as if they’re built for the sky. And for decades, researchers have speculated that the only time the swifts are on the ground is the 2 months a year they spend breeding. But without sensors light enough to be hefted by the birds—which weigh less than a tennis ball—this idea was impossible to test. Now, armed with tiny data loggers that can measure and record months of movement, a team of researchers has finally put a number to the birds’ frequent-flier habits. During their ten nonbreeding months, 19 monitored swifts spent more than 99% of their time aloft, the researchers report today in Current Biology. Most of the birds spent only a few occasional nighttime hours on the ground, and others never touched down at all. The data offer some hints about how swifts might manage their constant flight, including catching warm updrafts of air to glide during the day. Their larger suspicions confirmed, researchers can now turn to new questions about the swifts’ airborne lifestyle: for example, how they get a bit of shuteye—or survive without it—in their months on the wing.