Chinstrap penguins are avid nappers, taking more than 10,000 a day – but each one lasts just 4 seconds.
Dozing off for several short bouts every day is a common habit for birds. Pigeons, for example, can have hundreds of microsleeps a day, for around 10 seconds at a time.
But the chinstrap penguin (Pygoscelis antarcticus), a species named after the distinctive black strip under its head, has taken this sleeping pattern to the extreme.
In nesting season, male chinstrap penguins incubate their eggs while their partners go on long foraging trips. This means the males must remain vigilant to protect their eggs from seabirds such as skuas that prey on them.
Paul-Antoine Libourel at the Claude Bernard University Lyon 1, France, and his colleagues decided to investigate how they can stay on guard around the clock.
The researchers attached sensors to 14 nesting chinstrap penguins and remotely monitored their brain activity for 11 days.
After analysing the data, they found that each bird slept for roughly 11 hours a day, broken up into more than 10,000 naps lasting about 4 seconds each. These microsleeps were fairly spread evenly throughout each 24-hour period, says Libourel.
“It was really surprising that they were always sleeping like this,” he says. “It’s just a permanent state – they are constantly living between awake and sleep.”
This highly fragmented sleeping pattern allows them to keep a watchful eye on their eggs.
“I think we tend to underestimate how flexible sleep can be. As far as we know, all animals need to sleep, but sleep can look very different for species living in different environments,” says Anne Auslebrook at the Max Planck Institute for Biological Intelligence in Germany.
Since these penguins are successful in breeding and foraging, they don’t seem to miss out on the benefits of a longer rest, says Libourel. But Auslebrook says we can’t be sure about that yet. “One question that the study was unable to answer is whether such fragmented sleep comes at a cost.”