The common swift is a medium-sized bird that, superficially, appears to be somewhat similar to other birds such as House Martins or Barn Swallows. The swift, however, is much more remarkable. The common swift spends almost its entire life in the air, essentially never touching the ground once it learns to fly.
Typically, swifts are about 16-17 centimeters long and have a wingspan of about 38-40 centimeters. They are almost completely black or brown, with a small patch of grey feathers on their chins. The scientific name for the common swift, A. apus, means “without feet” and refers to their extremely short legs. The common swift uses its legs only to cling to vertical surfaces, as swifts typically never land on the ground as they would be too exposed to predators. Additionally, the ability to cling to vertical surfaces allows the swift to occupy spaces that could not be reached by other birds.
One particularly distinctive feature about the swift is its tail. Swifts’ tails have deep forks, and each end comes to a sharp point. The shape of the tail is not only aerodynamically efficient, but it also allows for the swift to make rapid, sharp turns while flying. This agility while flying is incredibly important to the swift as it feeds primarily on insects that it catches during flight. In addition to their very well-adapted tails, swifts have high-speed wings. High-speed wings are short, pointed wings that, combined with heavy wing loading and rapid wing beats, allow for extremely fast flight.
Swifts are migratory birds. In the summer during breeding time, swifts can be found throughout most of Europe, Western Asia, and Central Asia. Although their migration routes have not been extensively studied, swifts generally migrate to Equatorial and Sub-equatorial Africa. Recent studies of swift migrations have found that the some swifts will breed in Sweden and then migrate to the Congo.
Most adult swifts spend almost their entire lives in the air. Except for breeding, adult swifts will typically eat, drink, sleep, and mate while flying. During nesting season, swifts are known to fly at least 560 miles per day.
Many times, large groups of swifts – up to 2000 birds – will form feeding parties. These feeding parties position themselves over wetlands – lakes, river deltas, flooded areas – where small flying insects are commonly found.
One of the ways in which swifts are able to fly for such long distances without landing is that they have the ability to sleep while in flight. In order to be able to sleep while flying, swifts can enter a state called unihemispheric slow-wave sleep.
During unihemispheric slow-wave sleep, one half of the brain sleeps while the other half of the brain remains alert. Birds – and certain other animals – are able to achieve unihemispheric slow-wave sleep through the release of the neurotransmitter acetylcholine. Birds can undergo unihemispheric slow-wave sleep during either soaring flight or flapping flight.
In the case of the migrating swifts, unihemispheric slow-wave sleep allows the birds to migrate without having to stop to sleep, which both slows the migration and opens the swift to potential attacks by predators.
The swift unlike many other birds is extremely well-adapted to doing virtually everything while flying, and adult swifts do not technically have to stop flying at all during their lives. From their aerodynamic physiology to their ability to sleep while in flight, the swift has truly mastered the ability to fly.