The strange and strange world of sleep in animals

We may be able to sleep in all sorts of places, but nothing beats the enormous diversity of sleep habits in the wider animal kingdom. Animals can sleep on the wing, stand, sit in a tree or dive into the ocean. Nor do they have to close their eyes. The prevailing consensus is that all animals need sleep, although scientists can't be completely sure. In the first place, it can be difficult to tell when an object is asleep by simply observing its behavior. John Lisco of La Trobe University, who studies sleep in animals, says animals that seem asleep to humans may actually be awake and vice versa.

Eyes closed wide

While we close our eyes during sleep, some animals, such as fish and snakes, sleep with their eyes open. "They have no choice because they lack eyelids," says Professor Lisko. But ostriches also sleep with their eyes open – although they have eyelids (they actually have three pairs!) it turns out that these birds only keep their eyes open during slow (deep) sleep – they are more likely to maintain a certain degree of alertness, says Professor Lesko. When ostriches drift into REM sleep (the lighter stage of sleep where humans dream more lucid dreams) they close their eyes. Then there are animals that sleep with one open eye - like dolphins. These animals actually only sleep with half of their brain so they can observe predators while they sleep.

Any sleeping position is suitable

We generally prefer to sleep lying on the bed – on our side or back or – a less desirable position – on our stomachs. But nothing compares to strange and wonderful situations and locations where other animals sleep. The large frigate bird spends months at sea in search of food. During this time he sleeps while flying, taking short naps while flying in warm air currents. Sperm whales sleep vertically, swaying just below the surface of the water – their big heads end up at the top as they float, so the animals seem to be standing in the water. Meanwhile on Earth, cows and horses are among the animals that actually sleep standing, and cows even chew food while they sleep. They do this during slow-wave sleep, making it easier for them to quickly move their large objects in the event of a predatory attack. But once she goes into REM sleep, her muscles lose the ability to hold them and are forced to lie down, making them more vulnerable.

Flexible sleep schedules

Whether it's shift work or caring for young children, some of us don't get enough sleep at night and have to sleep at other times. Northern elephant seals face this dilemma when they have been at sea for months: how can they maximize foraging time and reduce their exposure to predators? Unlike dolphins, they cannot sleep with half of their brain awake and one eye open. So what to do? A study linking sleep monitors to elephant flats revealed that when she is in the ocean she limits her sleep to an average of just two hours a day. The only other mammal that sleeps so tightly is the African elephant. When elephant seals fall asleep for the first time in slow-wave sleep, they fall freely to the bottom of the ocean. But once she goes into REM sleep, she turns upside down and falls, spinning in a circle, suggesting that, like us, she is paralyzed during this sleep phase. And sometimes they hit the seabed and continue to sleep. Fortunately, they only sleep for short periods, and on some days they don't sleep at all when they're at sea. Once back on land, they sleep for about 10 hours a day.

Excessively fragmented sleep

Some of us complain of interrupted sleep when we wake up at night and may rely on naps to be able to get through the day. The truth is that there's no reason why we can't get our daily sleep in batches, as long as some of these naps are long enough to give us the deep sleep we need. But imagine how to survive only a short sleep? Researchers have found that Antarctic penguins get their sleep during nesting season by getting 10,000 short naps a day, each nap lasting only four seconds. Professor Lisco says: "This is an extreme level of sleep fragmentation. It's something that birds have." They are always alert: even domesticated parrots and pigeons rely on short sleep, albeit at a rate of only 1,000 a day.

Excessive sleep fragmentation

If humans are deprived of just one night of sleep, we may feel disturbed, but some birds may go weeks without sleep. Professor Lesko studied male pectoral sandbirds in the Alaskan tundra during the mating season and found that some deprived themselves of sleep for 19 days. This has paid off. "There was a huge variation in the amount of sleep the males got, but it was the males who were able to withstand constant alertness that generated the chicks." Professor Liscoe believes that being able to stay awake for a long time may send a message to females from the male that he has more energy and perseverance, and that he is a more attractive companion. Although he is unsure how males can tolerate such sleep deprivation, he believes it is an impressive achievement. "I challenge any human male to stay awake for three weeks and convince any woman in a bar to mate with him. I think they're going to find it hard.