Do birds sleep in flight?

Abstract

The following review examines the evidence for sleep in flying birds. The daily need to sleep in most animals has led to the common belief that birds, such as the common swift (Apus apus), which spend the night on the wing, sleep in flight. The electroencephalogram (EEG) recordings required to detect sleep in flight have not been performed, however, rendering the evidence for sleep in flight circumstantial. The neurophysiology of sleep and flight suggests that some types of sleep might be compatible with flight. As in mammals, birds exhibit two types of sleep, slow-wave sleep (SWS) and rapid eye-movement (REM) sleep. Whereas, SWS can occur in one or both brain hemispheres at a time, REM sleep only occurs bihemispherically. During unihemispheric SWS, the eye connected to the awake hemisphere remains open, a state that may allow birds to visually navigate during sleep in flight. Bihemispheric SWS may also be possible during flight when constant visual monitoring of the environment is unnecessary. Nevertheless, the reduction in muscle tone that usually accompanies REM sleep makes it unlikely that birds enter this state in flight. Upon landing, birds may need to recover the components of sleep that are incompatible with flight. Periods of undisturbed postflight recovery sleep may be essential for maintaining adaptive brain function during wakefulness. The recent miniaturization of EEG recording devices now makes it possible to measure brain activity in flight. Determining if and how birds sleep in flight will contribute to our understanding of a largely unexplored aspect of avian behavior and may also provide insight into the function of sleep.

First evidence of a 200-day non-stop flight in a bird

“…However, our data indicate that there are distinct periods of increased and decreased activity, which could go along with some kind of sleep in flight. It has been argued that locomotive control of flight is possible in slow-wave sleep, either unihemispherically as observed in dolphins or even bihemispherically 14 . Various birds carrying out long-distance flights are able to reduce sleep without the need for compensatory sleep afterwards.…”

“…Various birds carrying out long-distance flights are able to reduce sleep without the need for compensatory sleep afterwards. However, they still do sleep for some time and some other birds do show some kind of sleep deprivation after long-distance flights 14,15,22 .…”

“…Neuroscientists investigating the problem of sleep did not find evidence for a full recovery sleep in flight 14 . It was pointed out that periods of undisturbed post-flight recovery sleep may be essential for maintaining adaptive brain function during wakefulness 15 .…”

Sleeping on the wing

“…Collectively, this research provided such a compelling story that it is commonly assumed (or stated as an established fact) that flying birds fulfil their daily need for sleep by sleeping unihemispherically. However, evidence of long flights is not by default evidence of sleep in flight-recordings of sleep-related changes in brain activity are needed to determine whether birds sleep on the wing [1]. Moreover, the seemingly untenable alternative-birds stay awake during long flights-was made more tenable by our recent discovery that despite sleeping very little pectoral sandpipers (Calidris melanotos) can perform adaptively under & 2016 The Author(s) Published by the Royal Society.…”

Use of Telemetric EEG in Brain Injury

“…Interestingly, slow wave sleep can occur in one or both hemispheres at a single time and REM sleep occurs only simultaneously in both hemispheres of the brain. Since the eye connected to the "awake" hemisphere remains open, it allows the bird to have navigation information during most of time during a flight (Rattenborg, 2006). In sum, the study of EEG sleep pattern in different species could one day allow a better understanding of sleep disturbances.…”