Spending your nights sleeping for just four seconds at a time might sound like a form of torture, but not for chinstrap penguins, which fall asleep thousands of times a day, new research finds.
Scientists studying the birds on King George Island in Antarctica found they nod off more than 10,000 times a day, allowing them to keep a constant eye on their nests, protecting eggs and chicks from predators. In total, the birds manage 11 hours of snoozing a day – without ever slipping into uninterrupted sleep.
“Humans cannot sustain this state, but penguins can,” said lead researcher Paul-Antoine Libourel from Lyon Neuroscience Research Centre. “Sleep is much more complex in its diversity than what we read about in most textbooks.”
Researchers previously looked at penguin sleep in the 1980s, which involved capturing them, putting them in a shelter and watching them. They reported fragmented sleep for short periods of time, which they called “drowsiness”. In the latest research, experts found that this fragmented sleep was sustained for the whole day, showing the penguins are not “nodding off” into deeper sleep.
“Sleep in breeding chinstrap penguins was highly fragmented under all conditions and positions on land,” researchers wrote in the paper, published in the journal Science. The findings suggest “microsleeps can fulfil at least some of the restorative functions of sleep”. The penguins studied could sleep standing up or lying down.
Sleep seems to be ubiquitous among animals, but it makes them vulnerable to predation because they lose the ability to respond quickly to the outside environment. Libourel said: “Sleep is at the core of animal behaviour, and is also under selective pressure. Most sleep research is conducted in rats, mice and humans, but working on other species shows us at what point sleep is affected by environmental change.”
The researchers studied chinstrap penguins in the wild using electroencephalogram (EEG) monitoring and continuous video footage. Microsleeps were shown by sleep-related brain activity and eye-closure. They noted a slight increase in the depth of sleep at around noon, when risk of predation could be at its lowest.
For chinstrap penguins, one parent sits on the nest for several days at a time while the partner is away feeding. Extended sleep may put their eggs or young at risk of predation by brown skua birds or other penguins.
The researchers studied 14 penguins incubating eggs, out of a colony of more than 2,700 breeding pairs. The discovery that these birds are doing thousands of microsleeps lasting only four seconds is “unprecedented, even among penguins,” researchers wrote.
Studies have shown some species routinely sleep very little, seemingly without negative costs to their performance while awake. African bush elephants sleep on average for two hours day, and mostly while standing up, one study found. Sometimes they went 48 hours without sleeping.
In some species there are differences between the sexes: male fruit-flies need more than 10 hours sleep a day, while females are fine on four, and can survive on less than 15 minutes’ sleep without it seeming to impact their chances of survival.
Giant frigatebirds can spend months on the wing during ocean migrations. During this period they can sleep for less than an hour a day, while still navigating and hunting. When they get back to the nest they stock up on sleep, snoozing for nearly 13 hours a day.
Researchers wrote in the paper, published in the journal Sleep Advances: “Taken together, these systems challenge the prevalent view of sleep as an essential state on which waking performance depends.”
“The data reported by Libourel et al could be one of the most extreme examples of the incremental nature by which the benefits of sleep can accrue,” the researchers Christian Harding and Vladyslav Vyazovskiy wrote in a related article published by Science. They say the paper calls into question how much sleep can be altered before the benefits are lost.
They added: “Proving that sleeping in this way comes at no cost to the penguin would challenge the current interpretation of fragmentation as inherently detrimental to sleep quality.”
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