"Fish got to swim and birds got to fly", but the latter don't usually stay airborne full time. However, it turns out that one species of bird does just that, with some individuals not touching ground for almost a year.
Even more astonishingly, the record setters are not oceanic wanderers like albatross or frigate birds that have nowhere to land. Although common swifts (Apus apus) cross the Mediterranean, most of their time is spent over places where they could touch down if they wanted to.
"When the common swifts leave their [northern European] breeding site in August for a migration to the Central African rainforests via West Africa, they never touch ground until they return for the next breeding season 10 months later," said Professor Anders Hedenström of Lund University, Sweden, in a statement.
Many species travel much further, but so far no other species is known to do so without ever coming to the ground to feed, drink, or just rest.
By attaching tracking devices to 19 birds, Hedenström found some pikers roost overnight in mid-winter, but many don't stop flying until it is time to raise a family. The common swifts that do roost outside the breeding season are mostly juveniles, presumably too entitled and lazy to keep constantly airborne for 300 successive days like their dedicated elders.
Overall, the species spent more than 99 percent of those 10 months on the wing. One slacker bird dragged the average down by spending four whole nights stationary, but Hedenström kept the tracker on for a second year, by which time its longest rest, breeding season aside, was two hours.
Not all of the swift family are such gluttons for punishment. Chimney swifts (Chaetura pelagica) and Vaux's swift (Chaetura vauxi) not only frequently rest at night, but apparently think that humans owe them a living, using rooftops and, as the name suggests, chimneys to do so. Alpine swifts (Tachymarptis melba) do go for long periods without touching ground, but that is a more modest 6.5 months. By contrast, frigate birds, thought of as epic wanderers, spend only two months at a time without touching down.
Such a lifestyle means swifts have to do pretty much everything on the wing. They feed on insect swarms midair and drink raindrops or skim a mouthful of water from lakes. Hedenström confirmed many of his subjects molted in flight as well.
A swift swooping over water to catch insects or to get low enough to drink. Markus Tallroth
Hedenström found swifts maintain their airborne status by gliding on thermal currents during the day, but at night they fly almost non-stop. At dawn and dusk, they push themselves to heights as great as 2,500 meters (8,200 feet), although the reason for this remains obscure. However, this does allow them to pause their flapping for a while and glide slowly down. These twilight ascents had previously only been observed in summer, but Hedenström's tags revealed they occur all year round.
During the breeding season, common swifts spend their nights in the nest, along with frequent visits during the daytime.
