Research Group Avian Sleep
Do birds sleep during flight? Most creatures, including humans, need their daily amount of sleep. This has led to the general assumption that some birds, like the common swift, which is airborne day and night, are capable to sleep during flight. However, until now the scientific world lacked the technical means to determine whether or not birds sleep during flight. 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 alternate between both brain hemispheres, REM sleep always occurs simultaneously in both brain hemispheres. During uni-hemispheric slow-wave sleep, the eye, which is connected to the wake brain hemisphere remains open. This condition allows birds to continue visually navigating while asleep. When it is not necessary for the birds to watch their environment continuously, slow-wave sleep involving both brain hemispheres should be possible as well. However, the reduction in muscle tone, which is associated with REM sleep, makes it unlikely that birds experience this type of sleep during flight.
The miniaturization of electroencephalogram techniques (a measure of brain wave activity) nowadays makes it possible to measure brain activity during flight. We are planning to conduct such experiments by using a 20-meter-long wind-tunnel. This wind-tunnel, constructed in 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. Further, the projection of landscape images onto the walls and the floor of the wind tunnel during the flight experiments allow us to simulate that the bird is moving. A planetarium, installed above the wind-tunnel, mimicks a night flight to the bird.
Our experiments aim at unraveling the mechanisms of how birds sleep during flight and will shed light onto a largely unstudied aspect of avian behaviour.