Nowadays, people usually lie in bed alone or at most in pairs. Many animal species, on the other hand, prefer group cuddling. This has not been studied much so far, although it does reveal interesting peculiarities, such as Behavioral researchers now in the journal Ecology & Evolution explainBumblebees, for example, suppress their sleep when their offspring are present. Anubis baboons sleep less in larger groups. And meerkats have established sleeping traditions: differences in the sleeping times of neighboring groups can persist across generations.
Female mallards, on the other hand, are less alert during rest periods when there are more males in their group. The animals are apparently relying on the fact that potential predators are more likely to go after the drakes: because of their more contrasting plumage, they are more noticeable, as the scientists led by Pritish Chakravarty and Margaret Crofoot from the Max Planck Institute for Behavioral Biology and the University of Konstanz explain. The birds also exhibit a special phenomenon: hemi-sleep. One half of the brain slumbers while the other remains awake and alert. This phenomenon also occurs in dolphins and other species.
The article states that animals often have to make trade-offs when napping in groups: Chinstrap penguins, for example, are at a higher risk of being attacked by predators at the edge of a napping group. Far in the middle, however, there is a risk of being attacked by conspecifics.
In sleep studies, individual, isolated animals are usually observed
The researchers around Chakravarty and Crofoot are convinced that more attention needs to be paid to the social side of sleep in research. Up to now, sleep studies have usually only observed one animal at a time under laboratory conditions. The significance of the studies is therefore limited. Also because sleep in a natural environment can last for a different duration than in captivity and can even shift from daytime to nighttime sleep.
Modern technology now makes it possible to monitor groups in the wild in detail, and this should be used more intensively. It is very likely that key aspects of group behavior, including coordination, decision-making and cooperative behavior, are influenced by the sleep of its members. It is also interesting to find out how closely the processes in the brains of individuals sleeping together are linked.
But why do animals sleep in groups at all, even though they often fight at night or even get hit by their neighbors? One advantage is that social decision-making makes it easier to choose safe places to sleep, explains the team around Chakravarty and Crofoot. In addition, individual animals can then keep watch and warn the group of predators. In some cases, the warm cuddling also saves a lot of energy.
According to the researchers, analyses of anubis baboons have shown potential disadvantages: the larger the group, the greater the sleep deprivation caused by other members of the same species rumbling around at night. Particularly in cold, rainy conditions, there is a constant scramble for good sleeping places. In Japanese macaques, the alertness of one individual often disturbs the sleep of the other members.
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In principle, there are immense differences in the duration, structure and processes in the brain between and within species of sleep, the researchers explain. “Why animals sleep in such different ways remains a mystery.”
Some males suppress their sleep in order to be able to mate more often
One of the things that has a major influence on sleep is the love life. Male sandpipers, for example, suppress sleep for weeks during the mating season and male fruit flies also stop sleeping when they mate with females. Male broad-footed marsupial mice are known to sacrifice several hours of sleep per night for weeks in order to have more time for mating. In contrast, the sleep time of females remains unchanged. as researchers in the journal Current Biology reportedHowever, the marsupial mice have every reason to set their priorities this way: they only experience one mating season, after which they die. During this time they mate with as many females as possible. Why the males die after this three-week phase at the age of only about one year is unclear, according to the researchers. It is probably not due to lack of sleep.
The animal world has a number of other special sleep facets: some birds such as frigate birds and swifts sleep while flying, Arctic reindeer chewing their cudas studies have shown. Chinstrap penguins, on the other hand, only sleep for about four seconds on averagebut more than 10,000 times a day. And sea otters hold on to their paws when they lie on their backs in the water and take a nap – so that they don’t drift away from each other.
The fact that people sleep together in single beds or at most as a couple, at least in richer countries, is a relatively new phenomenon. Until modern times, Homo sapiens also slept mainly in groups. It was only with industrialization and increasing prosperity that single beds and private bedrooms became common in western cultures. However, in many parts of the world, sleeping together is still common.