Evidence that birds sleep in mid-flight

Area of Science:

• Ornithology
• Neuroscience
• Animal Behavior

Background:

• Birds undertake long-distance migrations, raising questions about sleep during flight.
• Unihemispheric sleep (one brain hemisphere at a time) is hypothesized for maintaining awareness during flight.
• Empirical evidence for sleep in flying birds has been lacking.

Purpose of the Study:

• To investigate whether birds sleep during flight.
• To determine the patterns and duration of sleep in flying birds.
• To assess the implications of in-flight sleep for migratory behavior.

Main Methods:

• Electroencephalogram (EEG) recordings were used to monitor brain activity in great frigatebirds.
• Data was collected from birds during extended flights over the ocean (up to 10 days).
• Sleep patterns were analyzed in relation to flight duration and behavior.

Main Results:

• Great frigatebirds demonstrated the ability to sleep in flight, utilizing both unihemispheric and bilateral sleep.
• In-flight sleep duration was significantly reduced (0.69 h/d) compared to land-based sleep.
• Ecological demands appear to restrict sleep opportunities during flight.

Conclusions:

• This study provides the first direct evidence of sleep in flying birds.
• Reduced sleep in flight challenges assumptions about sustained attention during long-distance aerial journeys.
• The findings highlight the trade-offs between sleep needs and ecological pressures in migratory birds.