Herbie Murray
Dolphins are conscious breathers, meaning they must remain conscious even during rest to avoid drowning. They have a few adaptations that allow them to rest effectively. One such adaptation is unihemispheric slow-wave sleep (USWS), where one hemisphere of the brain sleeps while the other remains active to watch for predators or obstacles and signal when to rise to the surface for air. Dolphins also slow their breathing while sleeping, reducing the number of breaths per minute. They may rest quietly in the water, vertically or horizontally, or sleep while swimming slowly next to another animal.
| Characteristics | Values |
|---|---|
| Dolphins' sleeping pattern | Dolphins sleep for a couple of hours at a time, mostly at night. |
| Sleep methods | They rest quietly in the water, vertically or horizontally, or sleep while swimming slowly next to another animal. |
| Breathing rate | Dolphins' breathing rate drops from 8-12 breaths per minute when active to 3-7 per minute while resting. |
| Blowhole | Dolphins need to retain control of their blowhole to avoid drowning during sleep. |
| Unihemispheric slow-wave sleep | One hemisphere of the brain sleeps while the other remains active to watch for predators or obstacles, react to danger, and signal when to rise to the surface for air. |
| Social behaviour | Dolphins tend to pair up and swim side-by-side while resting, providing safety in numbers. |
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What You'll Learn
Dolphins sleep with one eye open
Dolphins have evolved to rest and sleep in a way that suits their dynamic ocean environment. They have a few unique adaptations that allow them to rest and sleep without drowning. 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 that rise from the depths.
Dolphins enter a state of sleep called 'unihemispheric slow-wave sleep' or USWS. In this state, one hemisphere of the brain sleeps while the other remains active. The eye opposite the sleeping hemisphere also sleeps, so dolphins do indeed sleep with one eye open. The active brain hemisphere allows dolphins to watch for predators or obstacles, react to danger, and signal when to rise to the surface for air. This adaptation ensures they can breathe while sleeping and don't drown.
Dolphins also slow their breathing considerably when sleeping, with their breathing rate dropping from 8 to 12 breaths per minute when active to 3 to 7 breaths per minute while resting. They also have a higher tolerance for carbon dioxide, which means they can go longer without breathing. These adaptations allow dolphins to rest and recover energy efficiently without the need for deep sleep.
Bottlenose dolphins, for example, spend about a third of their day in this USWS state. They often pair up and swim side-by-side with a companion while resting. The social nature of dolphins provides safety in numbers, and they can take turns resting and keeping watch. This strategy allows them to rest effectively while staying safe and avoiding drowning.
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They rest with one half of their brain awake
Dolphins have evolved to have some remarkable adaptations that allow them to rest and sleep without drowning. One of the most fascinating strategies they employ is unihemispheric slow-wave sleep, or USWS. This means that they rest with one half of their brain awake, allowing them to remain vigilant even during sleep.
During USWS, one hemisphere of a dolphin's brain enters a state of sleep while the other half remains active and alert. This allows dolphins to continue swimming, watching for predators or obstacles, and most importantly, signalling when to rise to the surface for air. This ability to control their blowhole, a flap of skin that opens and closes, is crucial for dolphins to avoid drowning while sleeping. They must remain conscious enough to recognise when their blowhole is at the surface to breathe.
The social nature of dolphins also plays a role in their sleeping habits. Adult dolphins often pair up and swim side-by-side while resting, providing safety in numbers. Additionally, while some individuals rest, others may swim in wider circles, keeping watch for any signs of danger or opportunities to feed. This cooperative behaviour allows the resting dolphins to focus on their USWS without worrying about potential threats.
Dolphins typically spend about two hours at a time resting one side of their brain, and they may take several of these rest periods throughout the day and night. While they are not fully asleep during USWS, it is sufficient for them to function. Dolphins compensate for the lack of complete sleep thanks to their efficient immune systems, brain plasticity, thermoregulation abilities, and unique brain energy metabolism.
The ability to rest with half of their brain awake is an extraordinary adaptation that allows dolphins to thrive in their aquatic environment without the risk of drowning. It showcases the ingenuity and resilience of these fascinating creatures.
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They swim slowly next to another animal
Dolphins have evolved to rest and sleep while swimming slowly next to another animal. This behaviour is an adaptation to the challenges of resting in a dynamic and unpredictable environment like the ocean. Dolphins are highly social animals, and they tend to pair up and swim side-by-side with a companion while resting. This behaviour provides safety in numbers, as the companion can help alert the resting dolphin of any dangers, obstacles, or opportunities to feed.
Dolphins also slow their breathing significantly when they are sleeping, with their breathing rate dropping from 8 to 12 breaths per minute when active to just 3 to 7 breaths per minute while resting. This slower breathing rate helps them recover energy more efficiently during sleep. Dolphins enter a state of sleep called 'unihemispheric slow-wave sleep' (USWS), where one hemisphere of the brain and the opposite eye remain active and alert, while the other hemisphere sleeps. This allows them to rest while still being aware of their surroundings and knowing when to rise to the surface for air.
The behaviour of swimming slowly next to another animal while sleeping is particularly important for mother dolphins with newborn calves. The mother dolphin must keep swimming for the first several weeks of the calf's life, as the calf does not have enough body fat or blubber to float easily and will begin to sink if the mother stops swimming. So, the mother dolphin tows her calf along in her slipstream, a position called echelon swimming, while they both rest and sleep on the move.
Overall, the ability to rest and sleep while swimming slowly next to another animal is a crucial adaptation that allows dolphins to get the necessary rest they need while also staying safe and aware of their surroundings in the ocean.
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They float at the surface, vertically or horizontally
Dolphins have evolved to rest effectively and stay safe in the dynamic and unpredictable ocean environment. They have a few unique adaptations that allow them to sleep without drowning. One of these adaptations is floating at the surface either vertically or horizontally. This floating behaviour is called "logging" because a dolphin resembles a log floating at the water's surface.
Dolphins are conscious breathers, meaning they must choose to come to the surface and take each breath. Unlike humans, they do not have a breathing reflex that takes over during sleep. Therefore, they must remain conscious, even during rest, to avoid suffocating or drowning. To achieve this, dolphins enter a state of sleep called unihemispheric slow-wave sleep (USWS). In USWS, one hemisphere of the brain sleeps while the other remains active. The active brain hemisphere allows the dolphin to watch for predators or obstacles, react to danger, and signal when to rise to the surface for air.
While sleeping, dolphins also slow their breathing, with their breathing rate dropping from 8 to 12 breaths per minute when active to only 3 to 7 breaths per minute during rest. This reduced breathing rate is part of the marine mammal diving response, an adaptation to their aquatic environment. Additionally, dolphins have a higher tolerance for carbon dioxide (CO2). Their brains do not trigger a breathing response until CO2 levels are much higher than what humans can tolerate.
Dolphins typically sleep at night, but only for a few hours at a time. They are often active late at night, possibly to feed on fish or squid that rise from the depths. Studies of bottlenose dolphins using electroencephalograms (EEGs) to measure brain activity have shown that they spend about a third of their day asleep. Dolphins also have the advantage of safety in numbers due to their highly social nature. Adult dolphins tend to pair up and swim side-by-side while resting, with one eye closed to sleep and the other open to stay alert.
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They slow their breathing rate
Dolphins have evolved to have a higher tolerance for carbon dioxide than humans. Their brains do not trigger a breathing response until the levels of carbon dioxide are much higher than what humans can withstand. This is part of the marine mammal diving response, an adaptation to living underwater, which helps them rest.
Dolphins can slow their breathing rate from an average of 8 to 12 breaths per minute when active to just 3 to 7 breaths per minute while resting. This is an example of how dolphins have adapted to their environment, allowing them to rest and recover energy more efficiently.
Dolphins enter a state of sleep called 'unihemispheric slow-wave sleep' or USWS. One hemisphere of the brain sleeps while the other remains active. This allows them to rest while also being vigilant for predators or obstacles and signalling when to rise to the surface for air.
The social nature of dolphins also helps them rest effectively. Adult dolphins often pair up and swim side-by-side while resting. This provides safety in numbers, as other members of the pod can alert resting dolphins of potential dangers or opportunities to feed.
Dolphins have evolved these mechanisms to rest effectively in the challenging and unpredictable ocean environment, ensuring they get sufficient rest while staying safe.
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Frequently asked questions
Dolphins have a unique sleep pattern that allows them to rest one half of their brain while the other half stays awake and alert. This ensures they continue to breathe, maintain awareness of their surroundings, and surface for air when needed. They also sleep with one eye open.
Dolphins generally sleep at night, but only for a few hours at a time. They take short naps throughout the day and sleep in shifts for up to eight hours per night.
Dolphins are social animals, so it is common for them to sleep in pairs or groups. They stay close for protection and social bonding. Mothers with calves might sleep alongside their young, providing warmth and security.
