Everyone knows that dolphins are truly unusual animals, so it is not surprising that they always sleep with one eye open. If you’ve ever felt the need to sleep with one eye open, you have something in common with these extraordinarily intelligent animals.
Dolphins keep one eye open while they sleep. They do so because they are unable to fall into an unconscious state while sleeping. This is because dolphins must periodically return to the surface in order to breathe, and they must remain vigilant in case predators are about.
Dolphins and whales often sleep with one eye open to avoid being eaten by sharks. Like whales, dolphins and related Dalla porpoises sleep with one eye open so that half of their brains are asleep.
The way dolphins deal with this is by putting one half of their brain to sleep while the other half is still conscious and functioning. During sleep, the bottlenose dolphin turns off only half of its brain, along with the opposite eye.
A complex sleep system in dolphins that slumbers on the surface of the water, with half of the brain awake and the opposite eye open, while the other half of the brain sleeps with the opposite eye closed. During this sleep pattern, whales and dolphins do not go into a deep sleep state, only one half of the brain is unconscious while the other half is awake and awake.
Dolphin Brain Activity While Sleeping
When they sleep or rest, one hemisphere of their brain remains stationary, while the other shows signs of activity and stays awake. Dolphins rest in single-hemisphere sleep, which means they only rest half of their brains at a time. They can’t turn off both hemispheres of their brains and sleep deeply underwater, or they’ll drown. Dolphins sleep with only half of their brains and one eye open so they can watch for predators and other threats.
They need to stay conscious and sleep with their eyes open. Dolphins only close their eyes when they sleep; the left eye will be closed when the right side of the brain is asleep, and vice versa. Because dolphins need to get up periodically to breathe air and keep an eye out for potential predators, dolphins cannot curl up and sleep at night like land mammals can.
Thus, dolphins and whales can detect the approach of predators, and, just as important, only half of their brain reminds them to come up to the surface from time to time to get some air. Dolphins have a voluntary breathing system, so they must keep part of their brain on alert in order to breathe. In order to continue breathing while sleeping, whales and dolphins must control their blowhole, which is the skin that dolphins and whales voluntarily control. This means that in order for humans to consciously inhale and exhale in control of their actions, whales/dolphins must keep part of the brain awake so that it can activate each breath on its own.
Another difference is that humans breathe involuntarily (meaning we breathe all the time without thinking about it), while dolphins do not. The average dolphin breathes nearly 4-5 times per minute and can hold its breath for up to eight minutes while sleeping or resting.
Dolphins Sleep for Several Hours
Although breathing should continue with no more than a few minutes between breaths, dolphins sleep an average of eight hours a day, but only allow half of the dolphin’s brain to sleep at a time. Dolphin chronotypes usually fall asleep because their body needs it, not because they voluntarily give up. Even if half of the brain remains at rest, dolphins and whales do not drown and remain in a stable position during sleep.
According to the results of the study, it is assumed that it is not known whether this species is dreaming or even in a state of very deep sleep. Some marine mammals, including cetaceans (whales and dolphins), are the exception when it comes to sleep. From a distance, sleeping whales and dolphins can look like logs in the water; Sailors should stay away from resting whales and other marine mammals, as well as during the journey of these animals. Dolphins also have periods of deep sleep when they float on the surface of the water like a log.
It was thought that sleep involving only half of the brain at a time, or sleep with one hemisphere, evolved in dolphins to allow them to breathe on the surface of the water even when they were half asleep. Dolphins and whales can selectively use their organs, which helps them breathe underwater for longer periods of time and maintain sleep patterns in one hemisphere.
Dolphin Safety While Sleeping
Baby dolphins are particularly vulnerable to large marine predators such as sharks, so sleeping in one hemisphere helps keep them alive. Also, baby dolphins need to be close to their mothers in order to nurse, so the semi-awake state allows them to stay close and feed when needed.
The dolphin uses its watchful side to guard while sleeping, and this may be due in part to a need for security. This is how dolphins catch their Zzz: One side of their brain is awake while the other eye remains open to spot danger and rise to the surface to breathe.
The scientists also found that instead of falling asleep, one of the hemispheres of the dolphin’s brain is active. This study, done primarily on captive animals, found that sleep is most often non-hemispheric, meaning that it produces slow waves in one hemisphere of the brain while the other has fast waves typical of wakefulness.