Research Group Sleep and Flight in Birds
Do birds sleep during flight? Most creatures, humans included, need their daily allotment of sleep. This has led to the general assumption that birds, like the common swift, which flies through the night, also sleep on the wing. However, to date the scientific world has lacked the technical means to determine whether or not birds sleep while flying. The neurophysiological basis of sleep and flight leads us to postulate, that some forms of sleep could well be compatible with flying.
Like mammals, birds exhibit two forms of sleep: slow-wave sleep and REM sleep (rapid eye movement). While slow-wave sleep can occur alternately in each of the brain's two halves, REM sleep always takes place in both sides of the brain simultaneously. During unihemispheric slow-wave sleep, the eye connected to the awake side of the brain remains open. This condition might allow birds to continue visually navigating while asleep. If it is not necessary for the birds to watch their environment continuously, a version of slow-wave sleep involving both halves of the brain should also be possible. The reduction in muscular tone that accompanies REM sleep makes it unlikely that birds experience REM sleep in flight.
The miniaturization of electroencephalogram techniques (a measure of brain wave activity) now makes it possible to measure brain activity during flight. Our plan is to carry out experiments in a 20-meter-long wind-tunnel. The wind-tunnel, constructed at Seewiesen at the end of the 1990s, permits wind speed and air temperature to be adjusted according to the flight requirements of each bird species. It is also possible to project images onto the wall of the wind-tunnel and to simulate characteristic landscape elements through film sequences played on the floor. A planetarium is installed above the wind-tunnel so that the birds can be shown a starry sky to simulate a night flight.
The resulting findings concerning if and how birds sleep on the wing will add to our understanding of a largely unstudied aspect of avian behaviour and might also provide some general insights into the function of sleep.