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Dolphins

Short answer: Dolphins breathe voluntarily, so they can't fully lose consciousness for long. Instead they use unihemispheric slow-wave sleep, in which one half of the brain sleeps while the other stays awake.

During it, the eye opposite the waking hemisphere often stays open, which lets the animal surface to breathe, watch for threats and keep in contact with its group. The behavior is also seen in some other marine mammals and in birds. The footage shows dolphins swimming, with the presenter.

VideoWrite-up2 sources
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What should you know about Dolphins?

Quick facts. Each one stands alone and has a stable ID you can cite.

  1. Dolphins breathe voluntarily.

    DD-145-F01 · Write-up · Exhibit A (Voluntary breathing)

  2. One brain hemisphere sleeps at a time.

    DD-145-F02 · Write-up · Exhibit B (Half asleep)

Video transcript: Dolphins: Dolphins Sleep One Brain Hemisphere at a Time

Dolphins have a unique way of sleeping. DID YOU KNOW? While they do experience periods of deep sleep, they can't afford to fully shut down their brains for an extended time, as they need to surface to breathe. To overcome this challenge, dolphins rest one hemisphere of their brain at a time. This uni-hemispheric slow-wave sleep allows them to remain partially conscious and aware of their surroundings while resting. It enables dolphins to maintain basic bodily functions and respond quickly to any potential threats. NOW YOU KNOW!

Burned-in captions, read frame by frame (see transcript.md) · 25.0s Reel ·

Video coming soonDolphins · Instagram Reel
Dolphins: Dolphins Sleep One Brain Hemisphere at a Time Instagram Reel · · 25.0s

The write-up

Dolphins sleep one brain hemisphere at a time. The eye opposite the waking half often stays open.

  1. Exhibit A

    Voluntary breathing

    Dolphins breathe voluntarily.

  2. Exhibit B

    Half asleep

    One brain hemisphere sleeps at a time.

  3. Exhibit C

    One eye open

    The opposite eye often stays open.

  4. Exhibit D

    Staying alert

    It lets dolphins surface and watch for threats.

  5. Exhibit E

    Birds too

    Some birds sleep this way too.

Questions people ask about Dolphins

Why can't dolphins fully shut down?

They must surface to breathe.

Source: Write-up · Exhibit A (Voluntary breathing) · Wikipedia: Unihemispheric slow-wave sleep; Wikipedia: Dolphin

What is the sleep called?

Half the brain at a time.

Source: Write-up · Exhibit B (Half asleep) · Wikipedia: Unihemispheric slow-wave sleep

What often happens to one eye?

Opposite the waking half.

Source: Write-up · Exhibit C (One eye open) · Wikipedia: Unihemispheric slow-wave sleep

What does it let dolphins do?

While resting.

Source: Write-up · Exhibit D (Staying alert) · Wikipedia: Unihemispheric slow-wave sleep

Which other animals do it?

Some other marine mammals too.

Source: Write-up · Exhibit E (Birds too) · Wikipedia: Unihemispheric slow-wave sleep

Test Your Knowledge

All quizzes →

5 questions, all from this case file. Answers are revealed instantly.

  1. Why can't dolphins fully shut down?

    1. They breathe voluntarily
    2. They have no brain
    3. They never stop eating
    4. Water is too cold
    Show the answer

    Answer: A. They breathe voluntarily They must surface to breathe. Source: Write-up · Exhibit A (Voluntary breathing) · Wikipedia: Unihemispheric slow-wave sleep; Wikipedia: Dolphin

  2. What is the sleep called?

    1. Unihemispheric slow-wave sleep
    2. REM only
    3. Hibernation
    4. Torpor
    Show the answer

    Answer: A. Unihemispheric slow-wave sleep Half the brain at a time. Source: Write-up · Exhibit B (Half asleep) · Wikipedia: Unihemispheric slow-wave sleep

  3. What often happens to one eye?

    1. It stays open
    2. It glows
    3. It closes forever
    4. It turns red
    Show the answer

    Answer: A. It stays open Opposite the waking half. Source: Write-up · Exhibit C (One eye open) · Wikipedia: Unihemispheric slow-wave sleep

  4. What does it let dolphins do?

    1. Surface and watch for threats
    2. Fly
    3. Breathe underwater
    4. Grow faster
    Show the answer

    Answer: A. Surface and watch for threats While resting. Source: Write-up · Exhibit D (Staying alert) · Wikipedia: Unihemispheric slow-wave sleep

  5. Which other animals do it?

    1. Some birds
    2. No others
    3. Only fish
    4. Only insects
    Show the answer

    Answer: A. Some birds Some other marine mammals too. Source: Write-up · Exhibit E (Birds too) · Wikipedia: Unihemispheric slow-wave sleep

Cite this case file

Easterling, Marcus. "Dolphins." The Detail Department (DetailEnjoyer), case file DD-145, last updated Dec 27, 2023. https://detailenjoyer.com/case/dolphins/

Permalink: https://detailenjoyer.com/case/dolphins/ · Last updated

Markdown version

Cite a single fact by its ID, for example DD-145-F01 → https://detailenjoyer.com/case/dolphins/#DD-145-F01