Swifts remain airborne for 10 months at a time

Common swift, Apus apus. Photo by René Demoulin. 

The common swift looks like a torpedo with long thin wings. They occur throughout most of Europe in the summer where they make nests on the sides of cliffs and houses. These nests are constructed of material that they collect in flight and stick together with saliva. They migrate from Europe to sub-Saharan Africa in the winter, where they are observed foraging, but roost sites have never been found. In a paper last week in Current Biology a team of researchers lead by Anders Hedenström, attached accelerometers and geolocators to swifts caught in southern Sweden in the summer. They found that swifts spend the majority of the winter in flight, sometimes having only one 2 hour stop in the course of 10 months. This means that not only do they eat and drink on the wing, they also must be sleeping in flight. Previous research has shown that frigate birds, which remain in flight for 2 months at a time, sleep in flight with one half or even both halves of their brain. But when flying over the open ocean for 10 days, frigate birds only slept for about 40 minutes a day, which is much less than they usually sleep on land. It will be exciting to learn how much sleep swifts are actually getting in flight, as it is hard to imagine that they can subsist on 40 minutes a day for 10 months. But why do swifts do this? Why not find a nice place to roost for the night? Well roosting birds are sitting ducks, so to speak. A sleeping, roosting, bird is at its most vulnerable. The authors suggest that swifts may be particularly vulnerable because their adaptations for catching insects high in the sky, including their long thin wings and tiny feet, result in poor manueverability on or close to the ground. The best solution, therefore, is to stay aloft.