How Long Can a Common Swift Stay Airborne Without Landing?

The common swift (Apus apus) can remain airborne for up to ten months without landing — the longest continuously airborne period ever documented for any bird. A 2016 study published in Current Biology by researchers at Lund University tracked thirteen common swifts with miniature accelerometer backpacks across a full non-breeding season and found that some birds never touched down once, while the rest were aloft more than 99.5% of the time.

What the Lund University Study Actually Found

Scientists fitted thirteen common swifts with tiny accelerometer backpacks — lightweight enough not to interfere with flight — and logged every movement across the full ten-month non-breeding period. The data was unambiguous: three of the thirteen birds registered zero landings across the entire season. The remaining birds settled briefly on rare occasions, but even they spent more than 99.5% of their time in the air. The study, led by ornithologist Anders Hedenström and published in Current Biology in 2016, set a new benchmark for sustained avian flight, surpassing the previous record held by the alpine swift at roughly 200 days. For the common swift, 200 days is barely two-thirds of a typical season aloft.

Why the Common Swift Almost Can’t Land

The swift’s body is shaped almost entirely around aerial life. Its legs are so short and underdeveloped that if a swift lands on flat ground, it often cannot generate enough leverage to push itself back into the air. Without a raised ledge, a vertical wall, or a downward slope to launch from, a grounded swift is effectively stranded. This isn’t a flaw — it’s the outcome of tens of millions of years of natural selection. Legs that are never used offer no survival advantage, so evolution redirected that biological investment into the features that matter: long, scythe-shaped wings and powerful chest muscles built for near-continuous flight.

Why Swifts Climb to 10,000 Feet Twice a Day

Twice each day — at dawn and at dusk — common swifts ascend from low altitudes to between roughly 6,500 and 10,000 feet. The pattern is consistent and deliberate, but the reason remains one of ornithology’s more intriguing open questions. Radar studies have ruled out feeding as the primary driver: insect availability at those heights doesn’t explain the timing or altitude. The leading hypothesis is that swifts are using the unique polarized light of twilight to gather orientation and navigational cues — essentially reading the sky to calibrate their internal compass. The twice-daily climb may be the swift’s way of checking its position during an otherwise uninterrupted season of flight.

How a Swift Sleeps Without Landing

Sustained flight over months raises an obvious question: when do swifts sleep? The answer lies in unihemispheric slow-wave sleep — the same neurological trick used by dolphins and some migratory birds. A swift can rest one hemisphere of its brain at a time while the other hemisphere remains active, keeping the bird alert and airborne. During these rest phases, swifts glide on high-altitude air currents, minimizing active wingbeats while half the brain cycles through sleep. The result is a bird that is, at any given moment, simultaneously asleep and flying.

The Broader Significance

The common swift holds the outright record among birds for the longest documented continuous airborne period. It eats in flight, drinks by skimming water surfaces at speed, and is widely believed to mate on the wing as well. Its entire life — apart from nesting — is conducted in the air. For researchers, the swift is a remarkable case study in how evolution can push a single adaptation — flight — to its absolute biological limit, reshaping anatomy, physiology, and even neurology to serve one overriding function: staying up.