Penguin Sleep is Weird: Micronaps All Day

Animals in the wild are in constant danger of being eaten by prey. This is especially true for Chinstrap penguins. When penguins lay eggs, they must be hyper-vigilant of the brown skua that loves to eat penguins eggs. Failing to pay attention for even a minute gives the skua enough time to steal a tasty penguin egg. That leaves open a question? How do the penguins sleep? If they sleep, the skua will have plenty of time to steal an egg. In the paper, "Nesting chinstrap penguins accrue large quantities of sleep through seconds-long microsleeps" Dr. Libourel et al. discovered, that penguins take 4 second micronaps over the course of the day. Not only do they sleep for 4 seconds at a time, they also sleep for 15 hours a day, constantly switching between a state of alertness and a state of sleep.
 
Dr. Libourel and team were able to collect this data using wild penguins by making use of new portable EEGs. They attached these EEGs to 14 wild penguins. The penguins would undergo slow wave sleep intermittently, switching between quiet wakefulness and slow wave sleep every few seconds. Fascinatingly, sometimes only one hemisphere of the penguin's brain would be asleep at a time. This unilateral sleep is not as restful as bilateral hemisphere sleep, but allows the penguin to pay attention to the contralateral side of the awake brain hemisphere. In fact, hidden cameras revealed that the penguins close the contralateral eye when one hemisphere is asleep. 

Figure 1G from the paper. Blue is slow wave sleep and red is quiet wakefulness. Notice how each hemisphere has about 4 second bouts of slow wave sleep. Moreover, Occasionally both hemispheres will be asleep at the same time. Over a 24 hour day, the penguin will accumulate 15 hrs of sleep.

Additionally, the penguins also engage in short micronaps when hunting. While they sleep less, they still needed to sleep. Moreover, rather than being asleep for long periods of time, they engaged in the same 4 second micronaps. Presumably this keeps them alert to potential seal attacks. Interestingly, penguins needed to catch up on sleep when they returned from the sea, and would more frequently micronap.

While the improving technology allowed us to better understand penguin sleep, it opens a bunch of questions. First and foremost, why do us humans need uninterrupted sleep while many birds (including penguins) can have micronaps. The general consensus is that sleep is important for allowing the brain to recover and consolidate memories. It is still unclear how penguins accomplish these tasks while engaging in micronaps. 

Author: Alex White

Sourse: 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, 382(6674), 1026-1031. https://www.science.org/doi/epdf/10.1126/science.adh0771