Chinstrap Penguins’ Bizarre Sleep Routine Upends Our Understanding Of Rest

In the realm of sleep, humans are monophasic creatures through and through, getting at least seven to nine hours a night. Some of us attempt to break that sleep up into chunks for the sake of somehow making it more efficient or fit better into our busy lives. The sad truth is such polyphasic sleeping doesn’t come naturally to us, at least in our modern world. But for a certain bird of the Antarctic Oceans, it’s an unavoidable way of life.

In a study published Thursday in the journal Science, an international group of researchers found that chinstrap penguins — named for the black stripe running under their chins — engage in probably the most extreme form of polyphasic sleep. These cousins to emperor penguins take micronaps, 10,000 four-second ones per day, at least, while nesting on land, throughout their day. In total, these dapper birds accumulate about 11 hours of sleep which seems, on the whole, to be rather restorative for them.

Whether microsleep, especially among animals, imparts any restorative benefit to the sleeper has been a question of much debate, Christian Harding, a postdoctoral researcher at the University of California, San Diego, and Vladyslav Vyazovskiy, a professor of sleep physiology at the University of Oxford, who were not involved in the study, write in an accompanying editorial. “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.”

Microsleep for the win

Sleep connects nearly all creatures of the animal kingdom, although our sleep habits vary. In the wild, there’s a trade-off between safety and getting enough sleep as, understandably, that period of vulnerability is an open invitation to predators or anything else that threatens survival.

Therefore, to remain hypervigilant, many animals may resort to sleeping shorter durations. But as anyone who bombed their math test after a night of poor sleep knows, not getting enough shut-eye prevents you from operating at your fullest during your wakeful hours and, over time, can impact your quality of life. Whether this is also the case for animals remains uncharted territory due to the lack of understanding of how external environmental factors — not just a species’s biology — influence sleep.

To unravel some answers, the researchers tracked the sleep habits of chinstrap penguins. These birds spend most of their lives at sea but return to land each year to form large colonies where they build nests, breed, lay eggs, and watch over their young. The penguins are often preyed upon by skuas, a large seagull-like bird that likes to steal penguin eggs or eat the chicks. Penguin parents thus take turns foraging for food at sea and protecting the nest from skuas and other aggressive penguins within the colony picking fights.

In early December 2019, the researchers followed 14 chinstrap penguins nesting on King George Island off the coast of Antarctica. These birds had been previously captured and outfitted with sleep loggers, devices connected to electrodes surgically implanted in the penguin’s brain that record brain activity. The animals were also strapped with a GPS, a pressure sensor (measuring how far they dived when foraging), an accelerometer (to capture body movements and posture), and an electromyogram, a device for measuring muscle activity using an electrode implanted into the bird’s neck.

On average, a chinstrap penguin spent around 22 hours nesting, and when not nesting, they were out foraging. They tended to spend most of their nesting time lying down, but it wasn’t like they were taking it easy. Looking specifically at slow-wave sleep — a stage of sleep typically associated with bodily recovery — the researchers found that the animals slept either with both cerebral hemispheres (aka bihemispheric) or only one, also known as unihemispheric, which is also commonly done by other aquatic animals like dolphins and manatees.

What was so striking, though, was how short these episodes of dozing off were: just 3.91 seconds long, on average. Both the nesting and foraging penguin parents experienced more than 600 bouts of these slow-wave sleep patterns per hour, but it was far more for the nesting penguin since the foraging one tended to be awake most of the time while it was at sea. On average, the micronaps added up to the penguins getting around a whopping 11.5 hours to 12 hours of slow-wave sleep daily.

Unprecedented among penguins

While the study didn’t directly measure how restorative these microsleeps were, the researchers surmise that since it doesn’t hamper the animals’ breeding, these truncated naps offer a benefit that “can accrue incrementally.”

This sort of sleep is rather unprecedented among animals, even other penguins. For example, captive emperor penguins have periods of "drowsiness" where they alternate between being awake and slow-wave sleep-like patterns, but this state only makes up about 14 percent of their time. Similarly, little penguins, found in Australia and New Zealand exhibit bursts of slow waves during "quiet wakefulness" while inside small metabolic chambers. Their sleep resembles microsleeps in chinstrap penguins; however, little penguins have longer bouts of slow-wave sleep, averaging around 42 seconds. But one major reason for these differences among other penguin species could be due to their captivity.

Harding and Vyazovskiy say that these findings could illuminate our understanding of the interplay between environment and the biology of sleep and sleep control in general. For example, in humans, conditions that impact our sleep-wake states, such as sleep apnea, impact cognitive function and can lead to neurodegenerative diseases like Parkinson’s and Alzheimer’s disease.

“Thus, what is abnormal in humans could be perfectly normal in birds or other animals, at least under certain conditions,” they write.