Under ideal conditions, common swifts can cover more than 805 km per day for more than a week, report scientists. Seems like an unimaginable feat for such a tiny bird, but swifts have adopted a clever strategy that makes these epic migrations possible.
As a migrating bird, common swifts (Apus apus) are aptly named. These highly mobile creatures spend more than 80% of their lives in the air when not in breeding mode, and a good portion of this time is spent migrating from northern Scandinavia to their wintering destinations in western and central Africa.
For these long-distance migrations, scientists had previously estimated average speeds of 499 km per day, but new research published in iScience has updated this figure to 570 km/day. More impressively — not that this isn’t impressive enough — the new study shows that swifts can travel farther and faster than previously thought. At their fastest, swifts can cover more than 805 km each day during a nine-day stretch. The new paper was authored by Susanne Akesson and Giuseppe Bianco from the Centre for Animal Movement at Lund University in Sweden.
The researchers used miniature geolocators to track 45 adult common swifts during migrations in 2010, 2012, and 2014 (the devices weighed less than 3% of the birds’ body mass, as to not slow them down). Of these, 24 were re-captured later; swifts almost always return to their specific breeding sites, making it possible to recover their trackers after a single migration season. Akesson and Bianco managed to recover 20 swifts who recorded their movements during a full year, including both autumn and spring migrations.
As the data showed, “common swifts breeding in the northernmost part of the European range” covered, on average, around 9,900 km during the autumn migration and around 7,900 km in the spring, “exceeding those recorded for populations in south and central Sweden,” according to the study.
The swifts use a combined strategy to achieve these record-breaking journeys, “including high fuelling rate at stopover, fly-and-forage during migration, and selective use of tailwinds,” the scientists write. By eating small meals along the way, the swifts are able to reduce the “high energy cost of flight,” according to the study.
As noted, the birds also take advantage of winds. Somehow, they know when the winds will be the most favourable. The scientists aren’t entirely sure how they’re able to do this, but they suspect it’s a reaction to changing air pressure caused by passing weather systems. Regardless, the winds give the swifts a 20% boost during the spring as compared to the autumn. The winds are the biggest help when crossing the Sahara and the Mediterranean Sea. Interestingly, the winds may explain why the previous speed estimates for the swifts were too low.
The swifts may be the speediest migrators, but other birds are equally impressive long-distance travellers. Last year, scientists reported on a record-breaking flight made by a bar-tailed godwit (Limosa lapponica). This bird flew nonstop for 11 days, covering 12,854 km from Alaska to New Zealand. Scientists suspect that bar-tailed godwits have a special metabolism that makes this possible, along with an ability to go without sleep for an extended period of time.