Chinstrap Penguins Survive on 10,000 Four-Second Naps Every Day

If dark mornings and early rises make you want a few more hours in bed, think of the chinstrap penguins of King George Island. A new study shows that these birds only rest through microsleeps lasting a few seconds. The penguins were found to pack thousands of these short snoozes into each day. The findings, say researchers, expand the limits of sleep across the animal kingdom.

The research was published in Science.

Inside a bird's brain

King George Island, a snowbound rock 125 miles north of Antarctica, is home to a handful of scientific research bases, a Russian Orthodox church and roughly 3,000 pairs of chinstrap penguins (Pygoscelis antarcticus). The birds huddle through the breeding seasons in tight-knit colonies; guarding against predators like the brown skua (Stercorarius antarcticus). Chinstraps are also known as stonecracker penguins due to their ear-ringing calls.

Rock-bottom temperatures, shrieking birds and egg-hungry predators do not make for a sleep-friendly environment. But sleep isn’t optional. It’s one of the few behaviors that seems to be universal among animals. Previous sleep research, however, has mainly studied humans and rodents, says Dr. Paul-Antoine Libourel, a researcher at the French National Centre for Scientific Research (CNRS).

Libourel has a background as an engineer. “[Over] the last 10 years I have worked a lot on developing tools to record different types of animals in a freely moving condition,” he tells Technology Networks. Libourel was contacted by Won Young Lee, an expert in penguin behavior at the Korean Polar Research Institute, who pitched the idea of studying sleep in penguins at the end of the world.

Libourel was taken by the idea for two reasons, the first being that penguins have evolved to survive in extreme conditions. They withstand freezing polar winds while sheltering their eggs for weeks at a time, before embarking on an even longer period where they swim through the dark Southern Ocean in search of food. He also noted that there was very little previous research on how these birds slept and even fewer naturalistic studies. This scientific gap exists for a good reason: studying sleep in the wild is tough.

How to assess sleep

To truly prove that an animal is sleeping, and not just resting with their eyes closed, scientists must measure their brain activity. An electrode is placed atop the animal’s brain, sitting under the skin. Implanting these devices is a complex process. It’s even more involved on an icy rock miles from civilization. 

Libourel and his team set up in a container near the penguin colony. They would walk out to the colony, catch a penguin and affix a recording device and GPS tagger to detect movement. The birds were operated on under veterinary supervision and carefully monitored to make sure there were no side effects that might harm them or alter their behavior. In total, they recorded data from 14 penguins. Weeks later, the team returned to extract their recording device and analyze how their penguins had slept.

“In mammals and birds, sleep contains two states: slow wave sleep (SWS) and rapid eye movement (REM),” explains Libourel. The two phases are marked by very different brain activity. During SWS, the normally rapid firing of brain cells decelerates, while the strength of the individual waves increases. SWS is the main phase of avian sleep, says Libourel. REM is harder to study through brain waves alone. In France, the state is called paradoxical sleep, as it produces waves like those of an awake brain. Without an obvious marker for REM, the team instead focused on SWS.

The SWS data showed that the penguins “slept” for an average of four seconds per snooze. But they racked up 11 hours of sleep daily, by logging over 10,000 microsleeps. Libourel says that the team wasn’t surprised by these microsleeps, but were taken aback by the finding that the birds seemingly never engaged in long-term sleep over the 11 days of the study.

Changing how we dream of sleep

Many people, says Libourel, have an “anthropocentric” way of thinking about sleep. Humans sleep in long chunks, although Libourel says humans have been shown to engage in microsleeps while driving late at night. What separates penguins from people is that humans quickly lose function if denied long sleep periods. But the penguins Libourel studied appeared to behave normally. “This is an adaptation that they develop and that we do not,” he sums up. What remains unclear is whether there is some opportunity cost to not getting extended sleep. Would penguins breed twice as many chicks and catch twice as many fish given the chance to sleep for 11 hours straight? 

Libourel says that previous sleep work has focused on humans or rodents. The specifics of how the animal kingdom sleeps remain unknown. “We don't know whether the benefits of sleep are the same across the animal kingdom. We don't know if sleep deprivation has the same effect on all animals,” he explains. Finding out will take a lot of ambition. Libourel has that in spades. “I would love to record a cetacean,” he says. “A big whale in their own environment.”

Reference: Libourel PA, Lee WY, Achin I, et al. Nesting chinstrap penguins accrue large quantities of sleep through seconds-long microsleeps. Science. 2023;382(6674):1026-1031. doi: 10.1126/science.adh0771