We come into contact with some animals on a daily basis but seem to know very little on their sleeping habits. Humans are quite similar when it comes to sleeping habits; most of us sleep in a bed; occasionally we may snore or sleep talk and we all have a comparable sleeping position. However do you ever wonder how animals sleep in water or why some sleep with one eye open? Read on to find out more…
Off the ground
The albatross is a marine bird and spends a lot of time gliding over the sea looking for prey. The albatross is barely ever seen sleeping at sea as this would make it a very easy target for predators and they have only been recorded on land while mating; instead they can sleep while flying. Some scientists believe that certain sleep patterns can allows birds to navigate while asleep and flying, but little evidence shows this to be 100% accurate. Until further evidence is shown, the albatross sleep pattern remains a mystery although sightings of this bird flying with its eyes closed have been noticed.
Both the sloth and the leopard find time to snooze high up in the trees. Where the leopard drapes its body over branches and can balance safely; the sloth hangs from branches with its powerful sharp claws. Sloths mate and have their babies while hanging and it has even been recorded that dead sloths have been found still in this position.
The sloth is renowned for being one of the laziest animals around sleeping for about 16 hours a day when in captivity and moving around very slowly, however research has suggested that wild sloths sleep an average of 10 hours a day. Niels Rattenborg, of the Max Planck Institute for Ornithology in Starnberg, Germany conducted a study where he attached a device to the sloths which monitored their sleep. A few days later he recaptured the sloths and found that on average they only slept for 9.6 hours. So although they may move around in a sluggish manner they certainly do not need as much sleep; Dr Neil Stanley, an expert in sleep disorders at the Norfolk and Norwich University Hospital, UK told the BBC that animals seem to sleep a lot more when in captivity as they have all of their needs met.
When days roll into nights
The koala, bat and opossum are just some of the animals that can sleep for most of the day. The koala sleeps an average of 18-22 hours with the time spent awake either eating or grooming itself; the bat sleeps for a staggering 19.9 hours with the remaining hours searching for prey at night (insects are more readily available during the night). Lastly an opossum can sleep up to 18 hours however if you come across an opossum don’t always assume that it’s sleeping; ‘playing possum’ is a popular technique used by these animals when they feel threatened. Basically they are playing dead and even give off an unpleasant substance which makes them smell dead to predators; they can be in this involuntary position (its a psychological reaction which they can’t control) anywhere from a few minutes up to four hours.
Surviving on very little
On the other hand there are animals which can survive on little sleep. The giraffe sleeps for an average two to four hours a day; in the wild giraffes rarely lie down due to the dangerous predators which live in their habitat however when in captivity their environment is safe and they lie down but rise every so often to move circulation throughout their whole body.
Although scientists still do not have enough evidence to fully back up this fact, it is still used today as a promising theory. Sharks are thought to rarely ever enter the REM stage of the sleep cycle because they need to always be moving to draw oxygen through their gills to help them breathe. They are able to rest but scientists find it hard to point at what time of day and how this will occur due to the constant movement of the shark.
A popular method among migratory birds, especially the swainson thrush, is to take micro-naps. Flying for long periods of the day can leave the thrush feeling drowsy and sleep deprived so it heads to the ground for around 8 to 10 seconds to have a quick nap. In some cases the bird will use unihemispheric sleep (see below for further information) to stay semi-alert of potential predators.
What a strange way to sleep…
It is still a mystery today to many experts as to why flamingos balance on one leg while sleeping; with many theories surrounding this unique manner. One of the least popular theories is that flamingos alternate between legs to keep the other leg dry and stop it from going prune-like (just like humans when they stay in the bath for too long).
Another theory is that like some other animals, flamingos shut off half of their brain and sleep, while the other half is still functioning and alert. This may explain that the leg which is raised is the same side of the brain which is ‘sleeping’.
The other two theories which are more common and seem like more realistic approaches are related to hunting and energy conservation. The flamingo uses camouflage to trick its predators into thinking its leg is a long, thin tree (which is commonly found in lagoons) therefore retracting potential attacks. For energy purposes the flamingo tucks one of its legs into its body to relax the heart and pump blood easily around the body; the length of the birds legs would cause strain in the heart if it had to pump blood around two standing legs.
A horse spends around 98% of its day standing up and only needs one to two hours every couple of days lying down to catch up on their REM sleep requirements. Horses can become sleep deprived in very rare occasions which can cause the horse to collapse as it falls in and out of REM sleep.
The otter sleeps very lovingly with other members of the romp; they basically sleep holding paws, creating a raft-like manner to stop one or more of the otters from being separated from the rest if they were to accidently float away. Their long tails come in handy too; they wrap them around seaweed and kelp to keep their body afloat and to stop them from drifting away.
Some animals can shut off half of their brain while the other half is still fully responsive to the outside environment (this is called unihemispheric sleep), the half of the brain which is still functioning can also keep the animal’s eye open on that side too; this protects it from any danger.
Ducks usually sleep in groups by the river bank in a row, the ducks at the end of the row, like the dolphin and seal, can switch half of their brain off while the other half is fully functional and alert. The dolphin and the duck keeps one eye open (the side which the brain is functioning) to look out for predators and dangers which lurk in their environment. The seal however can keep one flipper working to help steer it through the water while it naps, it then rises to the top of the water for air; this can leave the seal sleep deprived as it continually takes short naps under water before catching air.
Our last point to make which we find very fascinating is about the walrus. They have pharyngeal pouches which are located either side of the oesophagus; these pouches are expandable and can hold up to 50 litres of water. As these inflate they act like life jackets and push the walrus vertical so its head is constantly bopping above the water helping it breathe while it sleeps (Animal Planet).