We cannot live without sleep. But it is both a luxury and a mystery. We still do not know why it is essential. But a small change can ruin the rest of the day. Animals sleep as well as psychiatrist Jerome Siegel says. However, he adds that how animals sleep is as numerous as the species of animals. Variations include sleep’s depth, duration, and its effect on the brain. This ranges from all-time dozing dogs to literally half-awake dolphins.
Animals Sleep Periods
We are a type of sleeper known as monophasic, similar to every other great ape species. This means that we sleep once for a long time during 24 hours. Orangutans, gorillas, bonobos, and chimpanzees thus all build platforms, or beds, on trees where they sleep. Gorillas usually need 12 hours of sleep while orangutans sleep for about eight hours, like humans.
Other privates and among most mammals, animals sleep in a polyphasic manner. This means, that there are multiple sleep periods that alternate with activity periods during 24 hours. The cycle of sleeping and waking lasts for around 83 minutes for dogs. The total time adds up to about 10 hours and 30 minutes.
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The great apes’ beds are the reason behind their long sleep. For example, monkeys sleep while balancing on branches. So they can react quickly to danger but it does not help the animals sleep extensively. Now, apes built platforms because branches could not hold them as their size grew. The platforms also let them lie down and be secure from predators. This more secure and deeper sleep increased the cognitive abilities of the apes on the following day.
Sleeping While Half-Awake, Literally
Unlike great apes, dolphins can keep half of their brains alert while the rest sleeps deeply. This literally lets the animals sleep with one eye awake and scanning for predators. Siegal says that basically, dolphins are always alert.
This pattern of sleeping is known as unihemispheric slow-wave sleep. Dolphins share this with eared seals, manatees, some birds, and other cetaceans. It is a deep sleep state where REM sleep is absent.
REM, or rapid eye movement, sleep is the state of sleep when the activity of the brain is highest. Breathing increases in rapidity and a temporary paralysis sets in most muscles. REM’s importance is still being debated as it has a role in learning and memory. The intelligence of dolphins is high without REM sleep as neurologist David Raizen explains. The muscle paralysis associated with REM sleep would result in them sinking and drowning.
But if only one side of animals sleeps at any point, then there is a curious question that Siegel adds. Does it mean that dolphins are awake or asleep? There has not been a simple answer to how these animals sleep so far.
Some types of birds can fly while half their brain sleeps, as well. Frigate birds fly over oceans for months at a time. During this time, they can both regularly sleep as well as sleep using half the brain while they are gliding or soaring. They only sleep while flying on air currents that are rising. This lets them gain altitude and not fall into the water. They totally sleep in bursts of 10 seconds while flying. While on land, the animals sleep for around 12 hours in bursts of 1 minute.
Fur seals sleep with half their brain as well while they swim. However, on land, they sleep with their entire brain.
Is Sleep Essential For Animals?
Animals can take a rest in a variety of ways, apart from sleeping. Siegel explains that sleep’s classic definition defines it as a reduced responsiveness and activity period which can be reversed rapidly. It also needs makeup sleep in case of a deficit.
Siegel adds that all mammals do not need this makeup sleep. Fur seals, for example, sleep much more when they are on land than when in water. However, no rebound sleep has been seen by the animals.
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Raizen says that fruit flies need sleep. In complete darkness, the animals sleep straight for 12 hours. When deprived of sleep, their next sleep is longer during the next cycle for sleeping. Their success and reproductive drive decrease as well, Raizen adds.
This is a similarity between mammals and flies. Members who do not get enough sleep do not perform well in tasks that require learning. However, the mortality rate remains unchanged even when sleep deprivation is extreme. Raizen explains that rebound sleep points towards homeostasis, a balanced system that supports how important it is for how animals sleep.
Animals Sleep And Life Balance
For animals, sleep might not look like the best or safest use of its time. They could have spent the time on survival or eating. However, Siegel explains that for nature, passing on your genes is all that’s needed.
The breeding for animals is limited to seasons. Breeding would not increase if they don’t sleep. As such, protecting their genes and their offspring is the best way to pass on the genes. As such, it is helped by how animals sleep.
He explains that it is similar to how staying awake for multiple nights would hurt our hearts and brains eventually. Most animals sleep because of the same reason. Big herbivores like giraffes and elephants get only around 2 hours of sleep during the night since they have to forage a lot. He explains that how animals sleep depends on their ecological role.