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Penguins in Antarctica have evolved an unusual sleeping strategy to manage the constant demands of parenting.
For the first time, scientists have measured the sleeping behaviour of adult chinstrap penguins in the wild by attaching sensors that measure brain waves.
Guarding their chicks from predators and wayward penguins in a crowded colony requires round-the-clock attention.
During the breeding season, adult chinstrap penguins nod off thousands of times each day – but only for an average of four seconds at a time.
Yet according to new research these short microsleeps, totalling around 11 hours per day, appear to be enough to allow them to function for weeks at a time.
Won Young Lee, is a researcher at the Korea Polar Research Institute and co-author of new study published in the journal Science.
"The team visited Antarctica for the first time in 2014, and since then, we have been studying penguins. When we observed penguins in the wild, it didn’t seem like they were getting any sleep. Humans sleep seven to eight hours every night, but penguins seemed to have a series of short sleeps. Maybe it’s because of predators nearby or other penguins made noises. We were curious whether penguins could get enough sleep in a day by getting a series of microsleeps."
Chinstrap penguins have a black line underneath their chin looking like the strap of a helmet, making them easy to identify.
For the first time, scientists have measured the sleeping behaviour of adult chinstrap penguins in the wild by attaching sensors that measure brain waves.
They collected data on 14 wild penguins over 11 days.
The idea for the study was hatched when Lee noticed breeding penguins frequently blinking their eyes open and shut during his long days of field observations.
"Past researchers had thought that microsleeps didn’t have any functions compared to normal periods of sleep and considered it something that occurs when a person is sleep deprived. But if you take a look at the result of the research, chinstrap penguins mostly depend on microsleeps. Although they are fragmented, if you put them all together, you can see that they spend half a day sleeping. Therefore, the study shows penguins get enough sleep through these fragmented periods of sleep."
The researchers did not collect data outside the breeding season, but they hypothesize that the penguins may sleep in longer intervals at other times of the year.
Researchers say they don’t know if the benefits of microsleep are the same as for long consolidated sleep.
It's unclear if chinstrap penguins in captivity share the same sleep patterns, but zookeeper Lindsay Ireland, says she's not surprised by the study's findings.
Ireland looks after Detroit Zoo's 81 penguins, including four chinstrap penguins, two males and two females.
"I'm not very surprised (about the results of the study), because we do see that similar behaviour here. They're very active first thing in the morning when the lights come on and then you'll see them, after they eat they'll kind of take a series of naps or they'll just be a little more sedentary in their location, whether it's on land or in the water."
Scientists have documented a few other animals with unusual sleeping patterns.
While flying, frigatebirds can sleep one half of their brain at a time, and northern elephant seals can sleep for 10 minutes at a time during deep dives, for example.
But penguin microsleeps appear to be a new extreme, researchers say.
"The smaller species of penguins like the chinstraps and the other ones that we have here will either sleep standing up with their head tucked underneath their flipper, or they'll actually lay down. We typically see them lay down when they're starting to take a longer nap. But mostly during the day, they’re short naps, they're standing up."
Daniel Paranhos Zitterbert who studies penguins at the Woods Hole Oceanographic Institution described microsleeping as an "amazing adaptation” to enable near constant vigilance.
