Imagine trying to get a full night’s sleep without ever closing your eyes for more than a few seconds.
For humans, it would sound exhausting, perhaps even impossible. We usually think of sleep as something that happens in long, continuous stretches. We go to bed, remain asleep for hours, wake up, and begin another day.
But in one of the harshest environments on Earth, a small Antarctic seabird appears to follow a radically different strategy.
Chinstrap penguins can fall asleep more than 10,000 times in a single day.
And many of those sleep episodes last only about four seconds.
It sounds almost unbelievable, yet researchers studying wild chinstrap penguins in Antarctica recorded exactly this remarkable pattern. Rather than relying on long periods of uninterrupted sleep, nesting penguins repeatedly slipped into extremely short bouts known as microsleeps.
Each episode was tiny, but together they added up to an extraordinary amount of rest.
Over 24 hours, the penguins accumulated more than 11 hours of sleep for each hemisphere of the brain, despite rarely remaining asleep for long at any one time. The findings were published in the journal Science in 2023 and offered scientists a striking example of just how flexible sleep can become when an animal has to balance rest with survival.
Life in a Crowded Antarctic Colony
Chinstrap penguins (Pygoscelis antarcticus) are named for the narrow band of black feathers that runs beneath their heads, giving the appearance of a tiny helmet strap.
They breed around Antarctica and the sub-Antarctic, often gathering in enormous colonies.
From a distance, such a colony may look picturesque: thousands of black-and-white penguins packed together against a dramatic landscape of rocks, snow and ocean.
For the penguins themselves, however, a breeding colony can be anything but peaceful.
It is crowded, noisy and full of constant activity.
Penguins call to one another, defend their territories, move between nests and occasionally become aggressive toward their neighbors. Parents must also protect their eggs and young from predators.
One particularly important threat comes from skuas, predatory seabirds capable of taking vulnerable penguin eggs and chicks. Other penguins can create problems as well, particularly when individuals compete for limited nesting space.
During incubation, chinstrap penguin parents generally share responsibilities. While one member of a pair stays with the nest, the other may head to sea to feed.
That creates a difficult biological problem for the bird left behind.
It needs sleep.
But it also needs to remain vigilant.
A long, deep sleep could potentially leave a nest vulnerable. Remaining continuously awake, meanwhile, would carry its own physiological costs.
Somehow, chinstrap penguins appear to have evolved a way of navigating this conflict.
They sleep — but only for seconds at a time.
More Than 10,000 Microsleeps
Scientists had noticed unusual sleep-like behavior in chinstrap penguins before the detailed study was conducted.
Won Young Lee of the Korea Polar Research Institute had observed nesting chinstrap penguins apparently dozing for extremely short periods in their colonies. He later worked with Paul-Antoine Libourel of the Lyon Neuroscience Research Center and an international team of researchers to investigate what was actually happening inside the birds’ brains.
Simply watching a penguin close its eyes would not be enough.
An animal may look sleepy without actually entering neurological sleep.
The researchers therefore needed to measure brain activity.
In December 2019, the team studied 14 wild chinstrap penguins that were incubating eggs on King George Island in Antarctica. The birds were equipped with specialized devices capable of recording electroencephalographic, or EEG, activity.
EEG recordings allowed the researchers to identify patterns of electrical brain activity associated with sleep.
The monitoring equipment also collected information about the birds’ movement and behavior, while GPS and other sensors helped researchers follow what they were doing both around the colony and during trips to sea. Video observations provided additional behavioral information.
What emerged from all those recordings was extraordinary.
The penguins were not simply taking occasional short naps.