ANIMALS: Some fish change colour at night. This is their way of camouflaging themselves. Most fish do this by dulling their bright colours and covering lightly coloured zones with a dark layer. The blue-green damselfish subdues its bright blue-green colour to a dull grey. This is sometimes referred to as its ‘pyjamas’. One theory is that dull colours save on energy.
HUMANS: Our bodies also go into energy-saving mode at night. We do not change colour, but our body temperature drops by approximately 1 degree Celsius so that we can sleep well.
ANIMALS: Every evening, chimpanzees build a nest to sleep in, usually in a tree. They make a nest by bending branches or other foliage into place to make a leafy platform to lie down on. Every member of the group makes a nest every day, except for the young chimps, who sleep with their mother. Sometimes they also make a nest during the day if it’s rainy. When chimpanzees go to sleep, they often pull a cover over themselves.
HUMANS: We also lie on a platform (bed) and cover ourselves (usually with a duvet). Chimpanzees and other primates sleep longer than humans. The theory is that this change came about when humans discovered fire. Fire allowed us to see longer and eat more calories. This gave us more energy and enabled us to stay awake for longer.
ANIMALS: Californian sea lions are so defenceless on land that they will never sleep deeply there. They sleep deeply when bobbing on or just under the surface. Although they come up to the surface regularly to breathe, this does not wake them up. Like other sea mammals, such as dolphins, sea lions engage in what is known as unihemispheric sleep: this means that each half of their brain takes turns to sleep, while the other half stays alert.
HUMANS: This phenomenon is also known in humans. American research from 2016 demonstrates that only half of our brain sleeps in a new place. This is the so-called “First Night Effect”. The assumption is that this is an instinctual survival strategy. Since you never know what can happen in a new environment, your brain can respond more quickly to dangerous situations if half of it remains awake.
HUMANS: Nearly every sleeping position you can think of can be found in the animal kingdom. Just like people, animals can sleep lying on their back, side, or stomach. Some animals, however, can also sleep standing on one leg, bobbing in the water, or even occasionally soaring in the air. Fruit bats, like the ones in the Monkey House in ARTIS Zoo, rest and sleep while hanging upside down from one or both hind legs.
ANIMALS: People usually sleep lying down. Various studies have shown that around 50% of people prefer to sleep on their side, and slightly more prefer their right side to their left. Approximately 40% sleep on their back and 10% on their stomach. Naturally, people can also sleep sitting down and some people can even sleep standing.
Auping recently adopted a chimpanzee at ARTIS Zoo, so we are also learning a little bit about animals’ sleeping rituals.