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Each nap – or “microsleep” – lasts only about 4 seconds.

Non-breeding emperor penguins held in captivity do frequently alternate between waking and short-wave sleep patterns in a state called "drowsiness" that resemble the microsleep patterns observed in chinstrap penguins.

“They always seem to be in a microsleep state,” says study co-leader Paul-Antoine Libourel, a research biologist at the Neuroscience Research Center in Lyon, France.

While the data is convincing, Cirelli notes that the researchers only studied the penguins during nesting periods, making it impossible to tell if the birds microsleep when they’re not parenting.

The other challenge is understanding how microsleep impacts the brains and bodies of the penguins.