The art of nodding off appears to have been mastered by breeding chinstrap penguins, who take more than 10,000 naps a day, with each nap lasting an average of four seconds, according to a new study.
The animals accumulate around 11 hours of sleep daily using this strategy, challenging a pattern observed in humans that fragmentation is detrimental to sleep quality.
“Microsleeps” or “micronaps” – seconds-long interruptions of wakefulness, which include eye closure and sleep-related brain activity – occur in humans who have had insufficient sleep, according to the study published in journal Science on Thursday.
However, nodding off can be inappropriate and even dangerous in certain environments, such as when driving a car, and it is unclear whether they are long enough to provide any of the benefits of sleep.
600 microsleeps an hour
To investigate whether microsleeps can provide any sleep functions and be a useful sleeping method in ecological circumstances that require constant vigilance, researchers in France, South Korea and Germany studied 14 wild chinstrap penguins who were incubating eggs in a colony exposed to a predatory bird, the brown skua, on King George Island, Antarctica, in December 2019.
During incubation, when skuas are known to prey on penguin eggs, one penguin parent is forced to guard the eggs or small chicks continuously while their partner is away foraging for several days, according to the study. They must also defend their nest site from intruding penguins, all while simultaneously needing to sleep.
The researchers identified their peculiar sleep patterns using remote electroencephalogram (EEG) monitoring and other non-invasive sensors to record brain activity, muscle tone, movement, position and temperature, as well as continuous video and direct observations.
They observed that the penguins in the colony engaged in more than 600 bouts of microsleep an hour.
The study authors said that “thousands of microsleeps lasting only 4 (seconds) is unprecedented, even among penguins.”
A small 1984 study found that captive little penguins put into metabolic chambers exhibited a state called “quiet wakefulness,” which resembles the microsleep of the chinstrap penguins. However, these bouts of sleep lasted much longer at 42 seconds on average.
A 1986 study found captive, nonbreeding emperor penguins to have fragmented sleep called “drowsiness,” which also resembles the microsleep pattern of the breeding chinstrap penguins. However, the emperor penguins only spent up to 14% of the time in that state.
In this study, 75% of sleep among chinstrap penguins was in episodes lasting less than 10 seconds, according to study coauthor and sleep ecophysiologist Paul-Antoine Libourel, who pilots and manages projects as part of the sleep team at the Neuroscience Research Centre of Lyon.
“This is not unique across the animal kingdom. There (are) other animals that are sleeping quite fragmented or in very short bursts of sleep. But, to our knowledge, they were not able to sustain such extreme sleep fragmentation of days and hours, day and night, and continuously (as these penguins). And this is what was very interesting in our findings,” Libourel told CNN Friday.
He added that through these short bursts of sleep the penguins could “sleep and remain vigilant” while incubating.
The researchers observed that even after the penguins had swapped with their partner to forage for food at sea, they slept in the same pattern upon their return to shore.
However, the bouts of sleep would last longer during their first hours back on land, indicating that the penguins needed to recover from losing sleep at sea, where they spend a lot of time actively awake doing activities such as diving.
The researchers also compared the sleep of those nesting in the center of the colony to those on the border, who are more exposed to predatory skuas and therefore need to remain more vigilant.
Those nesting at the border slept more deeply and had longer and fewer bouts of sleep than those at the center of the colony, which Libourel said “was quite unexpected” and “the reverse” of what they thought they’d find.
He put this down to a “noisy and disturbing environment” at the center of the colony due to a lot of penguins moving around, with those heading to the sea passing by the nests of the penguins incubating, making it a difficult environment to sleep in. Aggression among penguins and other interactions were also said to add to this.
Despite not directly measuring the restorative value of microsleeps, the researchers inferred that “the chinstrap penguins’ large investment in microsleeps,” and “their ability to successfully breed, despite sleeping in this highly fragmented manner,” suggests that “microsleeps can fulfill at least some of the restorative functions of sleep.”
They concluded that other animals might also have “the flexibility to partition sleep into short or long bouts, depending on their ecological demands for vigilance.”
An ‘adaptation’ for survival
Libourel said that they do not yet know how physiologically these penguins are able to sleep in this way and warned that sleeping in short bursts is not advisable for humans, since we do not have the same physiology as chinstrap penguins and we do not know whether sleep functions in the same way for us.
Rather, the study shows that “some sleep pattern that could be bad for us – I mean, that could induce some pathology that we cannot sustain – for other animals, could be an adaptation and help them for surviving,” he added.
Libourel said there is still a “big gap” in our understanding of the role of sleep, and the impact of human disturbance and climate change on sleep and animal life. “I think that’s why it’s important to study sleep. Sleep is a central in animal behavior,” he added.
In a perspective published in Science, Christian Harding, a postdoctoral scholar at the University of California, San Diego, and Vladyslav Vyazovskiy, a professor of sleep physiology at the University of Oxford, wrote that the study “calls into question not only the current understanding of how sleep architecture is regulated but also the extent to which it can be altered before the benefits of sleep are lost.”
They added that climate change and human activity “are applying increasing pressure on natural habitats,” which are “affecting the amount and the quality of sleep in wild animals.”
They said sleep studies such as this one “are the best way to exploit opportunities to study sleep in wild animals free from human influence while it is still possible.”
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