Penguins get 11 hours of sleep a day — in four-second bouts

And these micro-sleeps can fulfil at least some of the restorative functions of sleep say scientists

Thu, 14 Dec, 2023 - 12:14

Richard Collins

We are such stuff as dreams are made on, and our little life is rounded with a sleep.

A paper just published will interest card-carrying insomniacs. Their complaint, it seems, is shared by penguins. Constant vigilance is essential to penguins when nesting; parents must stay awake and alert at all times to protect their eggs and young from predators. Puccini’s Nessun dorma might be their anthem but, according to the authors of the recent paper, penguins still manage to enjoy ‘great nature’s second course, chief nourisher in life’s feast’.

We spend a third of our lives in the arms of Morpheus, son of Somnus. Infants need about 19 hours sleep each night, most adults get by on seven. Nor are humans the only creatures which nod off; almost all animals sleep. A mallard does so with both eyes closed when there are ducks on both sides of it, but with one eye open if the bird is exposed on one side. This, presumably, results in lower quality sleep.

Chinstrap penguins roam the Southern oceans off Antarctica. During their summer, which coincides with our winter, pairs converge on islands to nest. Several thousand chinstraps breed on King George Island in the South Shetlands.

Recording behavioral states in wild chinstrap penguins. (A) Penguin equipped with sleep and GPS loggers mounted on the back and a pressure logger mounted on a leg

Two eggs are laid in a crude nest of pebbles. Parents take turns incubating them and protecting the youngsters. Shifts last several days, the off-duty bird going to sea to forage. Danger comes from the skies; brown skuas are constantly on the prowl, ready to snatch an unguarded egg or chick. Rogue penguins are also a threat. Being hypervigilant, therefore, is imperative for parents. Nor, with only short periods of darkness at night that far south, is there respite for on-duty birds.

Scientists from Korea France and Germany focused on 14 chinstraps nesting in the King George colony. Using non-invasive remote controlled sensors and video cameras, they recorded body temperature brain activity and the eye movements of nesting birds.

Research in zoos during the 1980s had identified episodes of drowsiness and ‘quiet wakefulness’ in penguins. The results of the recent study confirmed this. Sleepy episodes, however, were extremely short-lived. ‘The penguins nodded off more than 10,000 times each day’ the authors say. Bouts lasted an average of 4 seconds each, ‘resulting in the accumulation of over 11 hours sleep (daily) for each (brain) hemisphere’.

But just getting enough sleep is not sufficient for human health. We need also to dream. Dog owners know that their pets experience vivid dreams. But do penguins dream?

Two main phases of sleep have been identified; Rapid Eye-Movement (REM) periods and ‘slow-wave’ ones. Most dreams occur during REM episodes, bur these could only be distinguished from wakefulness when a penguin was in the field of view of the cameras. The researchers, therefore, had to concentrate mainly on slow-wave sleep episodes.

What would a four-second dream be like? Would such a dream continue from one micro-sleep session to another, despite interruptions between them? The authors, like all scientists, are cautious. "Despite sleeping in a highly fragmented manner", they conclude "that micro-sleeps can fulfil at least some of the restorative functions of sleep".