The snoozing of penguins

A matter which turned up in the first instance in a recent number of the Guardian, followed by another article in the New York Times and another in the Economist. No doubt there were others which I did not see. It often happens that articles of this sort turn up long after the precipitating event, but in this case the precipitating article in Science has only appeared at the end of November. It is also the case that the anonymous piece in the Economist offers, to my mind, the best summary of the three of the article in Science.

All vertebrates sleep – a time when muscles are slack, thermoregulation is turned off and the animal is generally unresponsive to external stimuli. A lot of other animals – for example fruit flies – also sleep. With sleeping patterns varying a good deal across species, sometimes between the sexes. But despite much expenditure of effort, while we know that sleep is essential to humans and that prolonged sleep deprivation is fatal, we do not yet know what, in detail, sleep is for. Probably, in general terms at least, something to do with putting the body, in particular the brain, back to rights after a busy day’s work. A recharging of the batteries. But a recharging of a body which remains alive and a brain which remains active, not least on the evidence of dreams.

We do know that some animals – notably the ducks of reference 5 and sea animals – can do half sleep, where they sleep with one hemisphere (of the two available) at a time.

And we now have the study written up at reference 4. Which includes a ten day record of a dozen or so penguins during December 2019 on King George Island, a cold and wet, northern outpost of the Antarctic, at around 60°S. Not much darkness at this (midsummer) time of year. But a colonial time for hatching and nursing young. 

The penguins also need to look out for the brown skuas, large seabirds, which feed on both eggs and chicks. Bearing in mind that one of each pair of penguins is often absent, feeding at sea – so one might think that the other one needs to stay awake and alert.

But on this story, none of the penguins had any real sleep in this time, rather a very large number of microsleeps, mostly less than 4 seconds in duration. The penguins were only really active when they were at sea, and not all the time then. While on land, the total amount of quiet, REM sleep and bilateral micro-sleep (to the top of the blue band in the graphic above) seemed pretty steady, with the two flavours of unilateral micro-sleep making up the balance.

So during this time at least, the penguins got no proper sleep, just a whole lot of microsleeps, with quite a lot of those only half a brain at a time. But, as a species, they thrive and survive – so the sleep they do get must be enough.

A curious phenomenon, which any theory which seeks to explain what is going on during sleep will now have to accommodate.

References

Reference 1: 10,000 naps a day: how chinstrap penguins survive on microsleeps: Scientists studying the birds in Antarctica have found they snooze for 11 hours a day without falling deeply asleep - Phoebe Weston, Guardian – 2023. 

Reference 2: Penguins Take Thousands of Naps Every Day: The birds’ impressive ability to nod off may be an adaptation to an environment of constant interruptions - Carl Zimmer, New York Times – 2023. 

Reference 3: Why chinstrap penguins sleep thousands of times a day: But only for four seconds at a time – Economist – 2023. I had forgotten that there are no by-lines in the Economist. 

Reference 4: Nesting chinstrap penguins accrue large quantities of sleep through seconds-long microsleeps – P-A. Libourel, W. Y., I. Achin, H. Chung, J. Kim, B. Massot, N. C. Rattenborg – 2023. The original article in Science.

Reference 5: https://psmv4.blogspot.com/2021/05/let-sleeping-ducks-lie.html.