Sleep Habits Through the Animal Kingdom

Nature can be downright mindboggling when it comes to activities like sleep. Good quality sleep is more than just lying motionless for any animal, even humans. Sleep is an active process characterized by unique patterns of brain waves. Although there are many mysteries in nature, everything seems to work together in perfect harmony. Organisms adapt for survival in various ways, but every species is different from the next. These adaptations extend beyond physical traits and are reflected in the behavior and sleep patterns of other animals.

Humans need six to eight hours of sleep per day to function properly, and sleep deprivation dramatically reduces productivity. A giraffe only needs thirty minutes of sleep per day to function properly, and that half-hour of sleep occurs in five-minute increments. One must consider that being unaware and sleeping for extended periods (hours) may come at a high price in the wild.  Predators such as lions and other big cats can sleep for more extended periods because they face fewer risks of being attacked. Prey animals must be more careful and do not get to sleep as long, or they literally sleep with one eye open.

The commonality between (non-human) mammals and humans is rapid eye movement (REM) sleep associated with dreams. Humans and all other mammals exhibit the same brain activity level and increased heart rate during REM sleep. For example, dogs may bark or twitch during REM sleep, but humans often talk in their sleep. So, what are some unique sleep habits through the animal kingdom? You may find yourself surprised at how different animals sleep. 

Eight Animals with Unique Sleep Habits

• Bottlenose Dolphins – Dolphins, exhibit two sleeping methods: they rest quietly in the water, vertically or horizontally, or sleep while swimming slowly next to another animal. Individual dolphins also enter a deeper form of sleep, mostly at night. It is called logging because a dolphin resembles a log floating at the water's surface in this state. The dolphin shuts down half of its brain, along with the opposite eye. The other half of the brain remains alert. The attentive side typically watches for predators, obstacles, and other animals.
• Walruses – These marine mammals can sleep virtually anywhere. They typically sleep in water using their tusks to hang from ice floes. One study found that walruses can also easily forgo sleep for up to 84 hours. They can experience REM sleep in the water, but it is fleeting because they only hold their breath for about five minutes. On land, walruses can enter into a deep sleep that could last 19 hours.
• Elephants – Wild elephants tend to sleep less than elephants in zoos. Wild elephants sleep two hours a day, and sleeping occurs while standing. Observation of elephants in zoos showed that they slept between four and seven hours while standing up.

• Fish – Fish do not have eyelids, but they sleep to rejuvenate and heal their bodies. Although fish do not have the same anatomy as mammals, they show a reduced movement rate and a slower heartbeat. The slower heartbeat and reduced movement are indicators that fish conserve energy. Most fish hover or stay still, and their gill movements slow down. The majority of fish stay alert to danger even while they are sleeping, so they can make a quick escape.
• Ducks – Ducks allow half of their brains to sleep, but the other part of their brains stays awake, and the associated eye stays open. If ducks sleep in a row, then the ducks in the middle may sleep with both eyes closed. The two ducks on either end of the row will keep the eye closest to the other ducks closed, but the eye closest to the outside remains open. The ducks at the end of each row use their partial alertness to protect themselves and the other ducks.
• Ostriches – Ostriches exhibit two different types of sleep. The first type is called 'slow-wave sleep' or SWS, where the brain waves are slowed down but strong. Although SWS is referred to as deep sleep, the birds appear alert. In this stage, the ostriches stand very still with both eyes open and their necks upright. The second phase is REM sleep, where the ostriches' brain waves are fast and weaker. During REM sleep, the birds shut their eyes, which move rapidly behind closed eyelids. Once an ostrich becomes exhausted, they may lay their head down for fifteen minutes at a time.
• Bats - Bats are the most comfortable hanging upside down while sleeping. They tend to be small and compact, making it easier to circulate blood while hanging upside down. Their claws have special tendons that help them hang upside down with ease, exerting virtually no energy. They are nocturnal, which means they are most active at night. Some bat species can hibernate between five to six months and survive on a small amount of stored body fat.
• Snails – A snail's sleep cycle last two to three days. During that time, they spend half a day or slightly more asleep. Snails break their sleep into seven sections. Their time of wakefulness lasts 30 hours. However, to survive harsh conditions, a snail will hibernate for up to three years.

Top Seven Animals That Require the Most Sleep:

• Brown Bat: 20 hours per day
• Lion: 19 hours per day
• Giant Armadillo: 18 hours per day
• Opossum: 18 hours per day
• Tiger: 18 hours per day
• Cat: 14 hours per day
• Dog: 13 hours per day

Key Takeaway: In the animal kingdom, sleep patterns vary because evolution allowed species to fine-tune their sleep. An adult must get at least seven hours of sleep every night to remain at optimal health, but a giraffe can sleep for 30 minutes a day and be at optimal health. It merely depends on the environment.