Dolphins Sleep. The ancestors of cetaceans (like those of dolphins) were mammals that evolved on Earth. Some 55 million years ago, these animals returned to aquatic life although they are mammals to do this, they were forced to develop a special way of breathing.
How do Dolphins Sleep
All terrestrial mammals have what is called autonomous respiration, that is, it is not consciously controlled. On the other hand, aquatic mammals and, more specifically, cetaceans have what is called “conscious” breathing because they decide when they need air.
Even when they rest on the surface, they breathe only a few times per minute, these breaths are fast and deep and they allow them to fill their lungs up to 90% of their capacity.
By their need to swim and breathe, it is not unusual that many people are required, co since dolphins sleep. In this new article, you will discover how dolphins sleep and how they breathe!
What is sleeping?
To understand how dolphins sleep, you first need to know a little more about the process of sleep and awakening in mammals. The waking state and sleep can be easily distinguished from a physiological and behavioral point of view.
Sleep is characterized by two phases: slow or non-REM sleep and REM or paradoxical sleep. By being awake, the encephalography activity is desynchronized and shows waves of low amplitude but high frequency, conversely, when they are asleep, this activity synchronizes, increases the amplitude of the waves and its frequency decreases.
During the non-REM phase, the body’s muscular activity gradually decreases until it is canceled during the REM phase which is characterized by a muscle atony of the neck to the lower muscles (there is no of response from the muscles of the body). In addition, during the REM phase, rapid eye movements occur as well as a significant decrease in body temperature.
Dolphins sleep
It was in the 1970s that a group of Urss researchers discovered the answer to the question that brings us together today: how do dolphins sleep? Although sleep is composed of two phases, dolphins only know of one of them, the non-REM phase, which presents itself in a single-hemispheric way.
That is to say that when a dolphin sleeps, he just disconnects one of the hemispheres of his brain while the other continues his activity awakening, to say it otherwise we could say that one of the hemispheres is out of sync (awake) while the other is synchronized (asleep).
Moving from one state of awakening to one of sleep occurs in a progressive way, that is to say, while one hemisphere falls asleep little by little, the other awake at the same rate, it is, therefore, possible for the dolphin hemispheres to be half awake and half asleep, rather awesome, right?
The REM phase of sleep has not been identified in dolphins but has been identified in some cetaceans and, surprisingly, it is not unihemispheric and is observable throughout the brain.
Dolphins sleep only one eye
The single-species dolphin sleep occurs mostly during the night, the second half of the day, and when the sun sets. Studies show that both hemispheres have the same number of hours.
Having this type of sleep comes with a series of behaviors that allow the dolphin to continue to live and interact with the outside world. For example, one of the behaviors we can cite as an example is that dolphins only sleep with one eye.
When the right hemisphere of the brain enters the non-REM phase, the left eye closes and when the left hemisphere falls asleep, closes the right eye.
When a dolphin sleeps, he will be able to continue doing all the activities he wants to rest on the surface of the water, breathe, swim, and even communicate.
Why do not dolphins have a single-hemispheric REM phase?
One might think that dolphins do not have a REM phase because during this phase the body goes into muscular atony and the dolphin could sink, but scientists are not so sure …
In fact, if the dolphins had a single-hemisphere sleep phase, only half of the body would go into sluggishness and compensatory mechanisms would exist to allow them not to drown.
The most accepted current hypothesis is the following: a dolphin does not have REM sleep, because if he had one he could not tell the difference between dreams and reality.
Half of his brain would be analyzing real-world information while the other half would be analyzing dream information. If this were the case, the dolphin would be a prey too obvious for its predators …
How do dolphins breathe?
As we briefly touched on in the introduction to our article How dolphins sleep, the dolphin is a mammal like us, so it breathes with the help of its lungs. However, there is a difference in size between his type of breathing and ours …
We breathe automatically and unconsciously while a dolphin breathes in a calculated and conscious way. Each of his breaths allows the dolphin to fill between 80 to 90% of his total lung capacity, breathing 1 to 3 times per minute.
The dolphin is not equipped with nostrils and does not breathe through the mouth, he breathes through a hole on the top of his head called a vent.
Dolphins sleep only one eye
Stay awake to breathe or die while sleeping. To solve this dilemma, dolphins have developed a remarkable adaptation mechanism to the ocean environment that allows these marine mammals to “sleep” only half of their brain at a time.
“In the dolphin, breathing is a voluntary act, and reflex, as in humans. In the middle of the ocean, a loss of consciousness would be fatal. If he does not breathe, he dies, “says Jon Kershaw, Animal Manager at Marineland Park in Antibes. In order to “sleep while waking up”, the dolphin “turns off” one of its cerebral hemispheres, while the other half of the brain controls vital functions and, first and foremost, breathing.
During these periods of “single-hemispheric” sleep, the metabolism slows down and the cetacean hardly moves anymore. sleeping dolphins can be seen, floating on the surface, with an open eye and a fin that protrudes from the water. Then they change sides, “disconnect” the other half of their brain, and close the other eye.
The awake “half-brain” can thus ensure the ideal position of the body to stay on the surface and control the opening/closing of the vent.
This “unilateral sleep” could be established in the laboratory. The researchers were able to measure slow brain waves on the “sleeping” hemisphere, while the other was awake (fast waves). Twenty minutes later, the pattern was reversed.
dolphins sleep about eight hours a day in this way, in increments of a few minutes to two hours. “In fact, we do not really know if they sleep or they just rest because as soon as we arrive, the dolphins wake up suddenly, not like the sea lions that emerge more difficult,” says Jon Kershaw.
In captivity, Marineland healers can observe these half-sleep phases, especially during nighttime surveillance periods when a baby is born in Tursiops dolphins in the park. “We see them gently drifting on the surface of the basin, especially between two o’clock and five o’clock in the morning,” he said.
A recent study by neurobiologists at the University of California (UCLA) showed that young dolphins stay awake 24 hours a day during their first weeks. Mothers continually monitor the young and do not sleep either. This a finding that goes against the theories accepted so far on the sleep and development of mammals who are heavy sleepers at birth.
It will take several months for the baby dolphin to adopt the normal rhythm of life of cetaceans, five to eight hours of sleep a day, and the insomniac mother can finally agree to a few moments of rest.
Finally, researchers have looked at another mystery: do dolphins dream?
Almost all the studies carried out in the laboratory after the implantation of electrodes did not make it possible to prove the existence in the dolphin of periods of paradoxical sleep (called “REM”, Rapid Eye Movement), generally associated with the instants dream, which does not necessarily mean that dolphins do not dream.
This possible absence of paradoxical sleep in dolphins and cetaceans is in any case still an enigma for researchers.
