Nature is always surprising and raises questions that science strives to answer. Thanks to new technologies, we can observe animals in their natural habitats and thus study and understand many particularities that until recently were a mystery.
For example, how can it be possible that marine mammals – such as whales and dolphins, which need air to breathe just as we do – can live their entire existence in the water? And, if they need air to breathe, how do whales sleep without drowning? If you want to learn more about this issue, do not miss this article, because we tell you how whales and dolphins sleep and why they do not drown.
How whales sleep
Unlike humans, who don’t need to think to breathe, whales breathe voluntarily. Our breathing is reflex during sleep and we even continue breathing even if we are unconscious; Therefore, our brain manages to disconnect completely while we sleep and we can reach phases of deep sleep. Not so for whales, which even sleeping need to be aware of their breathing. So, don’t whales sleep? Does your brain not need to rest? The answer to both questions is yes: whales sleep and their brains need rest, too.
The big difference between marine mammals (whales) and land mammals (us) is that mariners have a brain that is able to connect and disconnect their hemispheres independently. Our brain, on the other hand, is unable to function using only one of its hemispheres. This peculiarity of marine mammals, such as cetaceans, allows them to sleep resting only half of their brain. In this way, a part of the brain remains alert, makes sure that the animal breathes, that no danger lurks and even allows it to move while sleeping.
This way of sleeping is called slow-wave unihemispheric sleep. It allows marine mammals to sleep in cycles, alternating the cerebral hemisphere that rests and the one that remains in a waking state. Thanks to him, these animals can survive during sleep. This original way of sleeping has the disadvantage that it hardly allows them to reach the REM phase of deep sleep and, when they do, it lasts just a few minutes.
This way of sleeping prevents whales from separating from the pod during sleep, as they can remain in motion next to each other. This activity during sleep is vital for cetaceans, as it minimizes the loss of body temperature due to the coldness of the waters, something that could lead to their death if they remained totally still. In addition, this contributes to the survival of calves, which grow in motion next to the mother while they are babies. Thanks to a technique called staggered swimming, the calf is placed in a position in which the mother’s own turbulence movement propels it and keeps it next to her. During the first weeks of life, the mother cannot stop at any time, otherwise the calf would drown, since it cannot yet float on its own.
How dolphins sleep
The system that dolphins use to sleep is the same as the one we have explained with whales. Their ability to function alternately with a single hemisphere of the brain means that dolphins can enjoy several full sleep cycles a day (approximately two hours each).
Although sleep habits vary by species, dolphins — unlike whales, which usually sleep in deep water and rise to the surface to breathe — prefer to sleep in shallow waters and some even float during sleep. A curious detail is that some dolphins rest horizontally, but others do so vertically.
However, dolphins have more peculiarities, because their sleep is deeper than that of whales and they can reach the REM sleep phase more easily, although it does not last more than a few minutes. In addition, they sleep with one eye open and one eye closed; The open is the opposite of the area of the brain that remains in operation. The part of the brain that remains awake is not one hundred percent, but it is able to detect movement and determine when it is necessary to climb to breathe.
In the sea, standing still can mean death, which is why most dolphins also move during sleep. Adult males do this in pairs and swim very slowly. Females and young swim in large herds, use the staggered swimming system, and also take turns keeping an eye out for natural hazards and obstacles.
Why whales and dolphins don’t drown when they sleep
To know how whales sleep without drowning, we need to know how they breathe. Their respiratory system has lungs just like ours and they are proportional to their size, that is, much larger than ours.
The equivalent of our nose is a hole they have over their head that is covered with a membrane of skin called a blowhole. According to experts, the movement of this “lid” is entirely voluntary, which means that the animal has to be conscious in order to open the blowhole, breathe and then close it when submerged so that no water enters its lungs.
That’s why whales and dolphins don’t drown when they sleep; Your respiratory system remains closed and water cannot penetrate to your lungs. It is almost impossible for a marine mammal to drown while sleeping, although it can suffocate due to lack of oxygen if it does not breathe in time.
The morphology of marine mammals has also developed other abilities as part of their adaptation to the marine environment:
- Their large lungs allow them to take in huge puffs of air.
- Your body tolerates higher levels of CO² than land animals, so your brain takes much longer to start the respiratory process.
- They are able to maintain their blood supply with “minimal services”, because when they sleep their blood only flows to the organs and vital processes. While they sleep, their digestion, for example, stops.
If you have been interested in this article and want to discover more curiosities of the marine world, do not miss these recommendations:
- How sharks breed
- How fish breathe
- What is the largest animal in the world
If you want to read similar articles to How whales and dolphins sleep, we recommend that you enter our category of The Animal World.