Throat penguins take an absurd number of naps per day: more than 10,000 (even when they swim)

Throat penguins take more than 10,000 naps a day – even while swimming. The naps last about 4 seconds on average. This means that the penguins sleep a total of almost 15 hours a day, but never for longer than 34 seconds at a time. That write French, Korean and Danish researchers this week Science.

Sleeping eight hours straight, as we do, is definitely not the standard. In fact, only primates sleep only once a day. Other animals take naps. In mammals they vary in length from 6 minutes in rats to about two hours in elephants. Marine mammals also nap, but one hemisphere of the brain always remains awake. This way they can always actively swim to the surface to breathe.

Mammal naps can take up a significant portion of the day, up to 19 hours in bats. Sleep has been much less studied in birds – especially in wild birds, because their brain waves are difficult to study from a practical point of view. From swifts, which stay in the air non-stop for up to 300 days at a time, is only assumed that they sleep while flying, but no one has ever measured it.

It was only in 2016 that the Danish researcher Niels Rattenborg submitted his report Nature Communications the first hard evidence that birds sleep while flying. He had attached a data logger to frigate birds (large tropical seabirds that fly non-stop for up to ten days) that measured their brain waves. This showed that the birds only sleep for 45 minutes a day while flying, spread over short naps. They usually do this with only one hemisphere of the brain at a time, but sometimes with their entire brain, especially during longer glides.

Apparently the life of the keel-banded penguins is exceptionally restless

The same researcher now participated in the sleep study with the throat strap penguins. These birds breed in enormous colonies, where there is constant restlessness. Predatory gulls regularly pass by to grab eggs or chicks. There is also a lot of aggression between the penguins themselves: they breed so close together that they constantly violate each other’s territory, for example on the way to the sea.

Rattenborg and colleagues wondered whether they would see this reflected in the sleep pattern. They put data loggers on the penguins and filmed them on the nest. The penguins appeared to sleep both standing and lying down. In both positions they took continuous micro naps. At sea they continued to do so while swimming and floating, but not while diving for fish.

Within one nap, the birds appeared to sometimes sleep unilaterally (for 1 second) and sometimes with their entire brain (2 seconds). Added up, those naps lasted an average of 4 seconds. In total, the penguins slept almost 15 hours a day: 8.5 hours with both hemispheres of the brain at the same time, and another 3 hours only with the left and more than 3 hours only with the right. This way, each hemisphere of the brain got at least 11 hours of sleep.

Such an absurd number of naps has never been seen before, not even in other penguin species. Apparently the life of the keel-banded penguins is exceptionally restless. All the more remarkable is the total amount of sleep they still manage to collect. Strangely enough, the penguins at the edge of the colony slept more, and for longer periods, than the penguins in the middle. This is the other way around for groups of ducks on the water, the researchers write. Apparently, neighborhood disputes require more vigilance than predatory gulls.