Penguin power naps: Racking up a day’s worth of sleep four seconds at a time

January 30th, 2024

Written by: Kara McGaughey

Ever drift off for a few seconds during a movie or late-night conversation? Maybe you insisted that you were “just resting your eyes” and were most definitely still paying attention? If so, you’ve experienced microsleep, a common phenomenon and a tell-tale sign that you have not been getting enough rest.1 While microsleeps do little to help us meet our sleep quota, a recent study suggests that this sort of sleeping is the norm for chinstrap penguins.2 In fact, chinstrap penguins are master microsleepers, nodding off more than 10,000 times per day! 

What does it mean to be asleep? 

Sleep is defined as a reversible state of reduced physical activity and disengagement from the environment.3 This definition helps distinguish sleep from rest (a state of reduced activity that happens while one is still engaged with their environment) and other states, like coma or death (in which reduced physical activity and engagement are not reversible). Sleep is also something your body regulates all on its own. For example, if you pull an all-nighter before a big deadline, you’ll probably spend the next day being pretty groggy, and when you sleep again you’ll begin repaying your “sleep debt” by sleeping for a lot longer than usual.

Importantly, while behaviors can help us distinguish sleep and wake states, differences in brain activity can also be helpful. The development of technology, like the electroencephalogram (EEG), which uses small metal discs placed on the scalp to measure the brain’s electrical activity, has provided a ton of insight into the brain activity patterns supporting sleep.4 Using EEG, it has been shown that sleep consists of two distinct components: rapid eye movement (REM) sleep and non-REM sleep.5 While REM sleep is, appropriately, characterized by rapid eye movements, non-REM sleep is defined by slow wave activity. As humans, about 80% of our sleep is this non-REM, slow-wave sleep.6

Why do the sleep habits of chinstrap penguins stand out?

A study published at the end of last year followed 14 chinstrap penguins nesting in a colony in Antarctica.2 Like humans, these penguins engaged in periods of both REM and non-REM (or slow wave) sleep. In addition, when the penguins spent long periods of time awake while foraging, they made up for the sleep they missed when they returned. However, despite these similarities to the way we sleep, two factors set chinstrap penguins apart: (1) how long their bouts of sleep last and (2) the fact that they can sleep with one side of their brain at a time.

Sleep duration: Throughout the 10-day experiment, the longest recorded bout of chinstrap penguin sleep lasted just 34 seconds, with their typical snooze time clocking in at under 10 seconds.2 Remarkably, the animals were still able to accumulate roughly 11 hours of sleep a day, but this required over 10,000 naps. That averages out to more than 600 naps every hour! Impressively, the penguins could engage in slow wave sleep during these naps regardless of whether they were standing up or lying down and irrespective of whether they were sleeping on land or in the frigid Antarctic water (although their mid-swim naps were less frequent).2

Unihemispheric sleep: While they spent a decent portion of their naptime with sleep-related brain activity that looked like ours, the study found that chinstrap penguins can literally sleep with one eye open, resting one hemisphere of their brain at a time.2 Scientists call this unihemispheric sleep, and it’s something these birds do thousands of times a day. Just like we can transition seamlessly between sleep and wake brain states, chinstrap penguins can easily transition between wakefulness and right-brain sleep, left-brain sleep, or whole-brain sleep. Sleeping with one eye open might help chinstrap penguins stay alert and ready to address any threats while still getting the rest they need.7 This incredible ability to experience sleep and wake states at the same time certainly puts human sleep to shame!

Scientists think that these two sleep-related oddities are what help chinstrap penguins effectively divide and conquer responsibility, particularly when their eggs need around-the-clock supervision.2 During this time, one penguin partner sits on the egg(s) while its mate forages for food. As these foraging trips can take days, it’s critical that the penguin left behind on egg duty stays as alert as they can for as long as possible. Maintaining partial brain activity while sleeping in short intervals helps them get the job done. As it turns out, a number of animals — like ducks and dolphins — also utilize unihemispheric sleep to meet their needs, often using their awake hemisphere to control basic functions, like swimming, monitoring water temperature, or surfacing to breathe.7-8

Why is sleep so important? 

While sleep isn’t always the priority, scientists agree that sleep is incredibly important — and not just for conserving energy! Sleep is also a time when your body engages in tissue cleanup and repair.9  As it turns out, while you’re fast asleep your brain is actually hard at work cleaning its crevices and taking out the trash. Essentially, sleep helps ensure the brain wakes up ready to put its best foot forward. It is also well established across animal species that sleep plays a role in cognitive processes, like learning and memory.10 Research shows that during sleep, in particular during slow wave sleep, the brain can reactivate groups of neurons involved in behavior during wakefulness. Reactivation allows the connections between neurons to be strengthened and the behavior (or the experience) to become part of the brain’s repertoire.11

In fact, sleep is so important that basically every animal sleeps or displays sleep-like behavior. Even very “simple” organisms, like flies or worms, meet the behavioral criteria of sleep; and jellyfish, which technically have a “nerve net” and not a brain, also exhibit a reversible sleep state during the night.3,12-13 This conservation of sleep behavior across such a wide range of species is perhaps the strongest evidence of its importance for health and survival. 

So, the next time you find yourself nodding off, maybe lean into the nap knowing that even though you might not be accomplishing much on the surface, your brain is still hard at work. After all, what’s one nap every now and then when penguins are out there taking thousands?

Interested in reading more? Check out our PNK archives for additional information on the different stages of sleep, how sleep improves learning, and the effects of sleep deprivation.

References

  1. Durmer, J. S., & Dinges, D. F. (2005). Neurocognitive consequences of sleep deprivation. Seminars in Neurology, 25(1), 117–129. https://doi.org/10.1055/s-2005-867080
  2. Libourel, P.-A., Lee, W. Y., Achin, I., Chung, H., Kim, J., Massot, B., & Rattenborg, N. C. (2023). Nesting chinstrap penguins accrue large quantities of sleep through seconds-long microsleeps. Science (New York, N.Y.), 382(6674), 1026–1031. https://doi.org/10.1126/science.adh0771
  3. Siegel, J. M. (2008). Do all animals sleep? Trends in Neurosciences, 31(4), 208–213. https://doi.org/10.1016/j.tins.2008.02.001
  4. Dement, W. (1958). The occurrence of low voltage, fast, electroencephalogram patterns during behavioral sleep in the cat. Electroencephalography and Clinical Neurophysiology, 10(2), 291–296. https://doi.org/10.1016/0013-4694(58)90037-3
  5. Roth, T. (2009). Slow Wave Sleep: Does it Matter? Journal of Clinical Sleep Medicine : JCSM : Official Publication of the American Academy of Sleep Medicine, 5(2 Suppl), S4–S5.
  6. Dijk, D.-J. (2009). Regulation and Functional Correlates of Slow Wave Sleep. Journal of Clinical Sleep Medicine, 5(2 suppl), S6–S15. https://doi.org/10.5664/jcsm.5.2S.S6
  7. Rattenborg, N. C., Lima, S. L., & Amlaner, C. J. (1999). Half-awake to the risk of predation. Nature, 397(6718), Article 6718. https://doi.org/10.1038/17037
  8. Mascetti, G. G. (2019, June 1). Meet the Animals That Literally Sleep with One Eye Open. Scientific American. https://www.scientificamerican.com/article/meet-the-animals-that-literally-sleep-with-one-eye-open/
  9. Siegel, J. M. (2003). Why we sleep. Scientific American, 289(5), 92–97. https://doi.org/10.1038/scientificamerican1103-92
  10. Maquet, P. (2001). The Role of Sleep in Learning and Memory. Science, 294(5544), 1048–1052. https://doi.org/10.1126/science.1062856
  11. Walker, M. P., & Stickgold, R. (2004). Sleep-Dependent Learning and Memory Consolidation. Neuron, 44(1), 121–133. https://doi.org/10.1016/j.neuron.2004.08.031
  12. Trojanowski, N. F., & Raizen, D. M. (2016). Call it Worm Sleep. Trends in Neurosciences, 39(2), 54–62. https://doi.org/10.1016/j.tins.2015.12.005
  13. Nath, R. D., Bedbrook, C. N., Abrams, M. J., Basinger, T., Bois, J. S., Prober, D. A., Sternberg, P. W., Gradinaru, V., & Goentoro, L. (2017). The Jellyfish Cassiopea Exhibits a Sleep-like State. Current Biology, 27(19), 2984-2990.e3. https://doi.org/10.1016/j.cub.2017.08.014

Cover Photo by Derek Oyen on Unsplash

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