Evie Summers
Whales and dolphins are marine mammals that spend their entire lives at sea. Unlike humans, who can breathe while asleep, whales and dolphins must remain partially conscious to trigger each breath and avoid drowning. They have two main methods of sleeping: resting quietly in the water, vertically or horizontally, or sleeping while swimming slowly next to another animal.
| Characteristics | Values |
|---|---|
| Methods of sleeping | Rest quietly in the water, vertically or horizontally |
| Sleep while swimming slowly next to another animal | |
| Enter a deeper form of sleep called "logging" | |
| Sleep and swim at the same time | |
| Young whales and dolphins rest, eat and sleep while their mother swims, towing them along in her slipstream | |
| Mothers also sleep on the move | |
| Blowhole | A flap of skin that opens and closes under the voluntary control of the animal |
| The animal must be conscious and alert to recognize that its blowhole is at the surface | |
| The animal must keep part of the brain alert to trigger each breath | |
| Marine mammal diving response | Reduce the number of breaths they take during rest periods |
| Breathing response is only triggered when CO2 levels are much higher than what humans can tolerate | |
| Brain activity | Only half of the brain "rests" while the other half remains alert |
| The alert half of the brain is used to watch for predators, obstacles and other animals |
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What You'll Learn
Whales and dolphins sleep in two basic positions
When resting quietly in the water, whales and dolphins shut down only half of their brain, along with the opposite eye. The other half of the brain remains awake and alert, watching for predators, obstacles, and other animals. This attentive side signals when to rise to the surface to breathe. After about two hours, the whale or dolphin will reverse this process, resting the active side of the brain and waking up the rested half. This is known as cat-napping.
Dolphins generally sleep at night, but only for a couple of hours at a time. They are often active late at night, possibly to feed on fish or squid, which rise from the depths. Studies have shown that bottlenose dolphins spend an average of 33.4% of their day asleep.
To avoid drowning during sleep, whales and dolphins must retain control of their blowhole, a flap of skin that is thought to open and close voluntarily. While they must remain partially awake to maintain a state of alertness to control their breathing, it is rare for a marine mammal to "drown". They won't inhale underwater but can suffocate from a lack of air.
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They must retain control of their blowhole
Whales are mammals and, as such, they have lungs and need to breathe air at the surface. Unlike humans, who can continue to breathe while asleep, whales must remain partially awake to maintain a state of alertness to control their breathing. This is because breathing in whales is "conscious" and under the voluntary control of the central nervous system (CNS). In other words, they must consciously decide to breathe, similar to how humans make a conscious decision to eat.
To avoid drowning during sleep, it is crucial that whales retain control of their blowhole. The blowhole is a flap of skin that is thought to open and close under the voluntary control of the whale. In order to breathe, a whale must be conscious and alert enough to recognize that its blowhole is at the surface. While humans can breathe while our conscious mind is asleep, as our subconscious mechanisms control our involuntary respiratory system, whales do not have this luxury. Instead, they must keep part of their brain alert to trigger each breath.
Studies have shown that only half of a dolphin's brain "rests" while it sleeps, with the other half remaining alert to ensure the animal continues to breathe. After a couple of hours, the dolphin will reverse this process, resting the active side of the brain and waking the rested half. This pattern is often called "cat-napping." While the exact mechanism has not been proven, it is likely that whales employ a similar strategy to dolphins, keeping one half of their brain alert to trigger breathing while the other half rests.
In addition to this, whales have other methods to help them hold their breath for longer than other types of mammals. For example, their brains do not trigger a breathing response until the levels of CO2 are much higher than what humans can tolerate. This is part of the marine mammal diving response, an adaptation to living in an aquatic environment that helps whales sleep.
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Marine mammals don't generally 'drown'
Marine mammals, such as whales and dolphins, have evolved to develop mechanisms to avoid drowning while sleeping. They have two basic methods of sleeping: resting quietly in the water, vertically or horizontally, or sleeping while swimming slowly next to another animal.
Firstly, it is important to note that marine mammals do not generally drown. They do not inhale underwater; instead, they suffocate due to a lack of air. This distinction is crucial as it highlights the unique adaptations of these creatures.
To prevent drowning during sleep, marine mammals must retain control of their blowhole, a flap of skin that opens and closes voluntarily. Whales and dolphins must remain partially awake to maintain a state of alertness and consciously trigger each breath. Their brains are programmed to trigger a breathing response only when CO2 levels are much higher than what humans can tolerate, allowing them to hold their breath for extended periods.
Additionally, dolphins have been observed to enter a deeper form of sleep, known as "logging," where they float at the water's surface. During this state, they shut down half of their brain, along with the opposite eye, while the other half remains awake and alert. This attentive side monitors the environment and signals when to surface for air. After a couple of hours, they switch, allowing the rested half of the brain to become active again.
These remarkable adaptations enable marine mammals to sleep without drowning, showcasing their evolutionary prowess in mastering aquatic environments.
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Whales and dolphins reduce their breathing rate while resting
Whales and dolphins are marine mammals that spend their entire lives at sea. They have lungs and breathe air at the surface, but they do not extract oxygen from the water like fish. To avoid drowning while sleeping, they must retain control of their blowhole, a flap of skin that opens and closes voluntarily. This means that, unlike humans, they cannot breathe while in a deep sleep as their subconscious does not control their breathing. Instead, they must keep part of their brain alert to trigger each breath.
Observations of dolphins and whales show that they have two basic methods of sleeping. They either rest quietly in the water, vertically or horizontally, or sleep while swimming slowly next to another animal. Dolphins have also been observed entering a deeper form of sleep at night, called "logging" because they resemble a log floating at the water's surface.
To conserve energy while sleeping, whales and dolphins reduce their breathing rate. Dolphins, for example, may average 8 to 12 breaths per minute when active, but their breathing rate drops to 3 to 7 breaths per minute while resting. This ability to hold their breath for long periods is another adaptation that helps them sleep without drowning.
In addition to reducing their breathing rate, whales and dolphins also exhibit a unique sleep pattern called "unihemispheric slow-wave sleep." During sleep, only half of their brain shuts down, while the other half remains awake and alert. This allows them to continue swimming, watching for predators, and surfacing to breathe. After a few hours, they will switch sides, resting the active side of the brain and waking up the rested half. This pattern is often called "cat-napping."
These adaptations allow whales and dolphins to rest and sleep without drowning, ensuring their survival in their aquatic environment.
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Only half of the brain is 'asleep' at a time
Whales and dolphins are marine mammals that spend their entire lives at sea. They are similar to humans in that they have lungs and need to breathe air at the surface. Unlike humans, they do not breathe unconsciously in their sleep. Instead, they must remain partially awake to maintain a state of alertness to control their breathing.
To avoid drowning during sleep, whales and dolphins must retain control of their blowhole, a flap of skin that is thought to open and close under the voluntary control of the animal. While sleeping, they shut down only half of their brain, along with the opposite eye. The other half of the brain stays awake and alert. This attentive side is responsible for watching out for predators, obstacles, and other animals, as well as signalling when to rise to the surface to breathe.
This process, known as cat-napping, allows whales and dolphins to rest while still being able to respond to their surroundings. After approximately two hours, they will switch, resting the active side of the brain and waking up the rested side. Dolphins, for example, spend an average of 33.4% of their day asleep.
The ability to keep part of the brain alert while sleeping is an adaptation to their aquatic environment. They also have mechanisms in place that reduce their breathing rate during rest periods, allowing them to hold their breath longer than other types of mammals. These adaptations ensure that whales and dolphins can sleep without drowning, even while swimming slowly next to another animal or floating at the surface.
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Frequently asked questions
Whales are conscious breathers, meaning they choose to come up to the surface for air. To avoid drowning, they must remain partially awake to maintain a state of alertness to control their breathing.
Studies have shown that only half of a whale's brain rests while sleeping, with the other half remaining alert. This allows them to breathe, as well as watch out for predators, obstacles, and other animals.
Whales typically sleep for a couple of hours at a time, usually at night. They may also enter a deeper form of sleep called "logging", where they resemble a log floating at the water's surface.
While it is rare for whales to fully drown, they can suffocate from a lack of air if they do not remain partially alert. However, young whales can eat, rest, and sleep while their mother swims and tows them along in her slipstream.
Whales have a blowhole, a flap of skin that they can open and close voluntarily. They must be conscious and alert to recognize when their blowhole is at the surface to breathe.
