Nodding off for a few seconds is an obvious symptom of insufficient sleep in humans, and can be harmful in some situations. However, a new study published on Thursday shows that chinstrap penguins slumber thousands of times in a day, accumulating their daily sleep need of more than 11 hours in brief bursts lasting only four seconds.
According to the authors, the flightless birds may have evolved this attribute due to their need to stay always watchful.
The researchers stated that the data suggest that, contrary to previous notions, the benefits of sleep can accrue slowly, at least in some species.
Chinstrap penguins (Pygoscelis antarcticus), called after the thin black band of plumage that ruins from ear to ear, are possibly the most common penguin species. Their present population is believed to be about eight million mating pairs, with the majority of them situated on the Antarctic Peninsula and South Atlantic Ocean islands.
When single parent penguins nest, they must keep an eye on their eggs and protect them from predatory birds known as skuas while their partners are out on multi-day foraging trips. They must also defend their nests from other penguins who may attempt to steal nest material. When a penguin partner returns, the duo switches roles.
In December 2019, a team led by Paul-Antoine Libourel of Lyon Neuroscience Research Centre implanted electrodes in 14 birds at a colony on King George Island. They employed accelerometers and GPS to monitor body movement and location, and they recorded electrical activity in the brain and neck muscles.
Researchers were able to identify various anomalies using camera records and direct observation over several days.
The penguins slept while standing or lying to incubate their eggs, with each bout lasting 3.91 seconds on average. They slept more than 10,000 times per day.
Penguins on the periphery slept longer and deeper than those in the centre, which can be explained by the excess noise and physical bumping that occurs in the centre of a colony, as well as the increased chance of nest material theft.
Although the scientists did not explicitly evaluate whether the birds were benefiting from sleep, the fact that the penguins were successful at reproducing led them to infer that this was the case, with the moments of neuronal stillness offering windows for rest and recovery.
However, in humans, diseases that disrupt sleep such as sleep apnea have impacts on cognitive function and may even induce neurodegenerative diseases such as Alzheimer’s.
“Thus, what is abnormal in humans could be perfectly normal in birds or other animals, at least under certain conditions”, scientists Christian Harding and Vladyslav Vyazovskiy said in a linked commentary piece.
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