Nesting chinstrap penguins take nodding off to the extreme. The birds briefly dip into a slumber many thousands of times per day, sleeping for only seconds at a time.
The penguins’ breeding colonies are noisy and stressful places, and threats from predatory birds and aggressive neighbor penguins are unrelenting. The extremely disjointed sleep schedule may help the penguins to protect their young while still getting enough shut-eye, researchers report in the Dec. 1 Science.
The findings add to evidence “that avian sleep can be very different from the sleep of land mammals,” says UCLA neuroscientist Jerome Siegel.
Nearly a decade ago, behavioral ecologist Won Young Lee of the Korea Polar Research Institute in Incheon noticed something peculiar about how chinstrap penguins (Pygoscelis antarcticus) nesting on Antarctica’s King George Island were sleeping. They would seemingly doze off for very short periods of time in their cacophonous colonies. Then in 2018, Lee learned about frigate birds’ ability to steal sleep while airborne on days-long flights.
Lee teamed up with sleep ecophysiologist Paul-Antoine Libourel of the Lyon Neuroscience Research Center in France and other researchers to investigate the penguins’ sleep. In 2019, the team studied the daily sleep patterns of 14 nesting chinstrap penguins using data loggers mounted on the birds’ backs. The devices had electrodes surgically implanted into the penguins’ brains for measuring brain activity. Other instruments on the data loggers recorded the animals’ movements and location.
Nesting penguins had incredibly fragmented sleep patterns, taking over 600 “microsleeps” an hour, each averaging only four seconds, the researchers found. At times, the penguins slept with only half of their brain; the other half stayed awake. All together, the oodles of snoozes added up, providing over 11 hours of sleep for each brain hemisphere across more than 10,000 brief sleeps each day.
Some marine mammals and other types of birds have strange or restricted sleep patterns too, often when staying alert is important. Dolphins can sleep with half their brain at a time, letting them remain vigilant for over two weeks straight. To stay wary of predators, mallard ducks can sleep with one half of their brain at a time too (SN: 2/6/99). And elephant seals dramatically reduce their sleeping hours while out at sea (SN: 4/20/23). But the sheer number of microsleeps seen in chinstrap penguins is unprecedented among animals, Lee says.
“It seems that the penguins do not have any time where they decrease their vigilance,” Libourel says. “Just a slight increase of microsleep-bout length around noon.”
The sleep pattern may help the penguins balance the brain’s need for rest with the demands of nesting. Predatory birds like brown skuas (Stercorarius antarcticus) patrol penguin colonies looking to plunder undefended eggs and chicks. “Penguin parents should be vigilant all the time during breeding to keep their offspring safe,” Lee says. There’s also constant commotion and noise in the colony disrupting sleep. Such extremely interrupted sleep may reflect the penguins’ flexibility in handling the stressors of raising chicks.
The many micronaps did appear to be at least partially restorative to their brains, since the studied penguins were able to function well enough to both survive and successfully raise their chicks. It’s unclear if the penguins’ sleep pattern changes after the breeding season.
“Sleep seems to be very diverse and flexible among species,” Lee says. “I believe that there are still many things unrevealed about animal sleep. By studying their sleep behavior, we can understand how animals have evolved to achieve brain restoration.”
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