Penguins take thousands of naps every day

Penguins are champion power nappers. Over the course of a single day, they fall asleep thousands of times, each for a few seconds, a new study shows.

Although animals have a wide range of sleep styles, penguins easily take the record for fragmented sleep.

“It’s really unusual,” says Paul-Antoine Libourel, a neuroscientist at the Neuroscience Research Center of Lyon in France, who helped make the discovery. “This just emphasizes that we don’t know much about sleep, and that all animals don’t sleep like we read in textbooks.”

The study was published Thursday in the journal Science.

Sleep science began in the early 20th century when researchers used scalp electrodes to discover that people produce slow brain waves while dozing.

They found similar wave patterns in mice, pigeons and other captive animals. Over time, scientists discovered that virtually every animal they studied remained unresponsive to their environment for some time each day. Even jellyfish sleep despite their lack of brains.

But How Animal sleep varies enormously. Brown bats sleep twenty hours a day, while giraffes spend less than two hours. Human brains switch off completely when we sleep, while seals can only switch off on one side; while the other is still awake, they can continue swimming while dozing.

As technological devices have become smaller and more powerful, researchers have found that the sleep patterns documented in captive animals differ significantly from those observed in the wild. In zoos, for example, sloths sleep almost 16 hours a day. But in a Panamanian rainforest, scientists observed how the animals slept less than 10.

In 2019, Dr. Libourel and his colleagues observed sleeping animals in an even more remote environment: King George Island, just 110 kilometers north of Antarctica.

Won Young Lee, a researcher at the Korea Polar Research Institute, invited the group to accompany him to the island, where thousands of breeding pairs of chinstrap penguins gather in nesting colonies to raise their young. In December 2019, the researchers equipped the penguins with electrodes and other sensors that recorded their activity for up to eleven days.

The birds split their time between swimming in the ocean and staying in the nests to keep their eggs and chicks warm. Between each trip to sea, which lasted about nine hours, the penguins spent an average of 22 hours caring for their young.

While in the ocean, the birds barely slept and spent only three percent of their time on the sea surface, the study found.

When the penguins returned to their nests, their brain waves slowed to a pattern typical of sleeping birds – but only for a few seconds. They woke up again, but fell asleep again. The birds went through this cycle 600 times per hour.

People can also experience this type of microsleep, but usually only after not having a good night’s sleep. It can be dangerous, especially if we fall asleep at the wheel of a car. But for chinstrap penguins, microsleep is the norm.

Dr. Libourel speculated that their sleep patterns reflect the extreme conditions in which they doze. Penguin colonies are noisy and busy, with birds constantly waddling back and forth from the ocean. The habitats are also dangerous: at any time, a gull-like bird called a brown skua can dive to a nest and eat eggs or chicks.

The fact that penguins can sleep so much despite all these disruptions suggests, according to Dr. Libourel that microsleep offers an essential advantage. Scientists have proposed many possible benefits of sleep. Some believe that the brain needs this to clear out its cellular waste, while others argue that the sleeping brain refines its cellular connections.

But Vladyslav Vyazovskiy, a neuroscientist at the University of Oxford who was not involved in the study, wondered how many penguins benefit from fleeting bouts of sleep. It is possible, he argued, that we are thinking about sleeping backwards. It could be the default setting for animal brains, and scientists should try to explain why animals wake up when they do.

“You basically spend your entire life sleeping, and you only wake up when you need to,” said Dr. Vyazovskiy.