Chinstrap penguin near Snow Island in Antarctica: one parent guards the brood, the other goes hunting for days on end
Photo: Ueslei Marcelino / REUTERS
When frontline penguins lay their eggs in November, it is primarily stressful for them: Predatory gulls of the genus Brown Skuas are after the offspring of the cute Antarctic birds. If the parents let their balls out of their sight, even for a short time, it could end badly.
How do chinstrap penguins survive the constant danger from the air? A scientific study published in the journal Science has now provided an astonishing answer: by having the animals sleep for only about four seconds – but around 10,000 times a day. In this way, they get about eleven hours of cumulative sleep.
"They show an unexpected sleep adaptation, a compromise between the need to sleep and the need to be awake," ecophysiologist Paul-Antoine Libourel of the Lyon Neuroscience Research Centre in France, lead author of the study, told Reuters.
"This has not been documented before," adds behavioral ecologist and co-author of the study, Won Young Lee of the Korea Polar Research Institute in Incheon.
Microsleep while standing or lying down
The researchers collected data in December 2019 from 14 penguins hatching eggs in a colony of around 3,000 breeding pairs on King George Island in Antarctica. They measured electrical activity in the brain — evidence of sleep activity — using a method called electroencephalography. The researchers also recorded videos of the birds and used other bio-logging devices, such as GPS monitors and accelerometers, to track their location and body movements.
While guarding their nests, the penguins dozed off briefly on average about 10,000 times a day, sometimes as many as 15,000 times. They closed their eyes, whether standing or lying down, the brain briefly lowered the activity: an interruption of the waking state for a duration of only a few seconds. Microsleep.
Is it possible that other animals do the same?
Microsleep can be dangerous in humans, for example in traffic or even in the cockpit. Chinstrap penguins benefit from this. "They don't show any obvious negative consequences of sleep fragmentation," Libourel said. "Since the birds can reproduce and feed efficiently, we believe that the function of sleep can also be fulfilled in this disturbed way." Co-author Lee hypothesizes that some other animals use similar sleep strategies. However, this has not yet been sufficiently documented.
Chinstrap penguins have a black feather band under their chin, which is why they are also called chin-striped penguins. Adult penguins are about 70–80 centimeters tall and weigh about 3–6 kilograms. They are one of the most abundant penguins in Antarctica.
They usually live with their breeding partner in a kind of monogamous bird marriage. The females usually lay two eggs in a circular nest made of stones, from which the chicks hatch about 37 days later. During the breeding season, males and females share parental duties, with one constantly guarding the eggs or chicks, while the other spends several days foraging in the freezing ocean. (By the way: penguins only taste salty and sour.)
Chinstrap penguins form colonies, which researchers have described as very noisy and very foul-smelling. The penguin droppings of such colonies are even examined by satellite from space.