In the wild, nesting chinstrap penguins get more than 11 hours of sleep per day—but not all at once, according to a new study. 

The study, published in Science, found that these birds nod off thousands of times per day but for only around four seconds at a time, cumulatively accruing their daily sleep needs while remaining continuously vigilant over their nests. 

Sleep seems to be ubiquitous throughout the animal kingdom. Typically characterized by immobility and the relative loss of ability to sense and respond to the surrounding environment, sleep can render animals vulnerable to predation. 

In humans, insufficient sleep can lead to nodding off, the seconds-long interruption of wakefulness by eye closure, and sleep-related brain activity. Such microsleeps can be dangerous, like when they occur while driving. However, it’s unclear if they are long enough to provide the same restorative functions that longer bouts of sleep are known to. If microsleeps do cumulatively fulfill sleep functions, they could provide an adaptive strategy for some species under ecological circumstances requiring constant vigilance. 

Paul-Antoine Libourel, PhD, and colleagues studied sleep behavior in a colony of nesting chinstrap penguins (Pygoscelis antarcticus) in Antarctica. While nesting, a single penguin parent is often required to guard their nest from predatory birds and intruding penguins while its partner is away feeding for several days at a time. Extended periods of sleep would put their nests and offspring at risk. 

Using remote electroencephalogram (EEG) monitoring and other noninvasive sensors to record sleeping behavior in freely roaming and nesting penguins as well as continuous video and direct observations, Libourel et al were able to identify peculiar patterns in the penguin’s sleep. They found that the birds did not engage in prolonged periods of sleep and instead were observed to fall asleep frequently—accumulating more than 11 hours of sleep per day over more than 10,000 microsleeps lasting only four seconds on average. 

According to the authors, the findings suggest that, given the breeding success of these penguins, the benefits of sleep can accrue incrementally and those microsleeps can fulfil at least some of the benefits of longer sleep bouts. 

“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,” write Christian Harding and Vladyslav Vyazovskiy in a related perspective. “Although sleep bout duration is sensitive to many variables and differs widely among species, the seconds-long microsleeps of chinstrap penguins are markedly brief.”

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