For the first time ever, scientists have officially recorded birds sleeping during flight. Previously, it had been conjectured that birds sleep while flying, especially when they make continuous journeys that last from days to possibly even weeks.
Birds seem able to continue with normal tasks that require physical engagement, such as flying and obtaining food, while running on minimal, or non-existent, amounts of sleep. In contrast, humans are completely unable to do such a thing, because our bodies shut down if we do not receive proper amounts of sleep.
How do birds sleep on land?
While alternative sleeping patterns have been observed in birds on land, no definitive proof had been found that birds utilize these same patterns while in flight until now. On land, birds such a Mallard ducks use a technique called “sleeping uni hemispherically” when they feel they may be in a situation that could pose a threat.
Some ducks will sleep on the outside of the group, turning one half of their brain off, while the other half is awake so they can be alert for potential danger. Ducks keep their outward facing eye open and the controlling side of the brain on to assess any possible problems.
Conversely, scientists do acknowledge that some birds may have “evolved a way to cheat on sleep.” Male sandpipers can survive on virtually no sleep during mating season when they compete for female sandpipers. Until now, it was unclear what method birds use while in flight.
Sleep in Flight
Swiss scientists developed a device to track birds’ sleeping patterns during flight. Niels Rattenborg and Alexei Vyssotski created a small electronic to monitor birds’ electromagnetic waves and measure if types of sleep were occurring, such as short wave sleep (SWS) or rapid eye movement (REM).
These scientists study great frigate birds that nest on the Galapagos Island, with help from the Galapagos National Park and Sebastian Cruz, an Ecuadorian seabird biologist. Frigate birds will spend weeks flying on foraging missions, sometimes traveling thousands of kilometers.
The scientists received some expected, but also some surprising, results. The devices attached to the frigate birds revealed that they stayed fully awake during the day, but once night began, they occasionally entered into SWS.
Though these periods of SWS only lasted for minutes at a time, the birds frequently allowed both sides of their brains to turn off. This complete sleep did not affect their ability to fly. Perhaps even more surprising, there were instances where the birds would fall into REM sleep, and still successfully fly.
According to Rattenborg, this didn’t surprise him because “REM sleep episodes only last several seconds in birds” unlike in humans where we enter the cycle for hours. Birds are much more capable of entering a deep sleep and still maintaining the physical activity they’re doing, since REM occurs for such a short period of time.
Though the birds’ performance does not seem to be impacted by this small quantity of sleep, which amounts to around 42 minutes a night during their foraging missions, scientists believe they may be sleep deprived.
This conjecture seems likely, considering that frigate birds sleep, on average, twelve hours a day when they’re on land and sustain deeper periods of sleep. Rattenborg hopes to be able to continue studying the birds and learn more about how sleep, and lack of it, affects all animals.