These Penguins Take 10000 Little Naps a Day

Chinstrap penguin

In adult humans, eight hours of sleep is considered ideal, ideally consumed without interruption during the night. Babies and toddlers need more sleep, divided into multiple stages, as sleep-deprived parents are well aware. Animals also require sleep; chimpanzees, our closest living relatives, need around ten hours; domestic cats sleep for 16 hours; and sloths, living up to their name, can sleep up to 20 hours. Birds like swifts can even sleep while flying, with each hemisphere of their brain taking turns.

Thousands of Micro-Naps

Biologists have discovered a similarly bizarre sleep pattern in a bird species in Antarctica: Adélie penguins (Pygoscelis adeliae), named for the thin black band across their throat, also sleep with only one hemisphere of their brain at a time. Specifically, they sleep for about three hours with one hemisphere and nine hours with both, averaging a fairly typical eleven hours per hemisphere daily.

Even more remarkable is how these rest periods are distributed throughout the day, especially during breeding seasons. This penguin species, known as the most quarrelsome in the entire penguin family, takes thousands of short naps each day, each lasting only a few seconds, as reported by an international team in the journal Science, which also featured the penguins on its current cover.

It takes the chinstrap penguin 20 winks to sleep once - or a little longer. penguen
It takes the chinstrap penguin 20 winks to sleep once – or a little longer.

It is well known that penguins generally display unusual sleep patterns as a result of the day-night rhythms in Antarctica, where it can be bright or dark all day. Consequently, penguins are neither strictly diurnal nor nocturnal but rather both. Researchers have long known that Emperor penguins, for instance, sleep only for a few minutes at a time.

However, the sleep behavior of Adélie penguins, studied by French neurobiologist and sleep researcher Paul-Antoine Libourel (Neuroscience Center of CNRS in Lyon) and an international team on King George’s Island off West Antarctica, is even more extreme. To study their sleep behavior, researchers used advanced tools such as EEG remote monitoring (for 14 individuals) and non-invasive sensors, along with video and direct observation.

Analysis revealed that nesting Adélie penguins did not engage in longer periods of sleep but instead took extremely frequent short naps. The researchers counted more than 10,000 micro-sleep phases, averaging only four seconds each but accumulating to over eleven hours of sleep per day for the penguins.

These brief attention phases likely help the birds safeguard against aggressive peers and other threats without succumbing to sleep deprivation. Another surprising finding was that penguins nesting at the colony’s periphery were less stressed than those in the center. They slept more deeply, longer, and with fewer interruptions. Therefore, the penguins’ own quarrelsome peers may be more sleep-deprived than the predatory seagulls, considered the true enemies of nesting penguins, their eggs, and chicks.

What is Sleep, Anyway?

Considering the breeding success of Adélie penguins, these micro-sleep phases seem to fulfill the crucial functions of longer sleep phases. According to Libourel and his colleagues, despite the brevity of these slumber phases, the penguins engage in slow-wave sleep, often referred to as deep sleep in humans. These new findings ultimately lead back to the fundamental question of what sleep really is. According to biological and physiological definitions, it is typically characterized by immobility and the relative loss of the ability to perceive and react to the environment, as noted by Christian Harding and Vladyslav V. Vyazovskiy in an accompanying commentary in Science.

Until now, it was believed that such brief interruptions of wakefulness in humans either indicate illness or occur under extreme fatigue. In the case of Adélie penguins, micro-sleep seems to cumulatively fulfill essential sleep functions and represents an adaptation strategy to a lifestyle that demands constant vigilance. The question remains whether such micro-sleep phases could theoretically be as restorative as longer sleep phases in humans, assuming they do not occur behind the wheel of a vehicle.