# Dolphins (DD-145)

> 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.

- Department: Nature (also Science)
- First published: 2023-12-27
- Last updated: 2023-12-27
- Permalink: https://detailenjoyer.com/case/dolphins/
- Original Reel title: Dolphins 🐬
- Author: Marcus Easterling (DetailEnjoyer), The Detail Department

## Quick facts

- **DD-145-F01**: Dolphins breathe voluntarily. _(Write-up · Exhibit A (Voluntary breathing))_
- **DD-145-F02**: One brain hemisphere sleeps at a time. _(Write-up · Exhibit B (Half asleep))_

## Write-up

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

1. **Voluntary breathing**: Dolphins breathe voluntarily.
2. **Half asleep**: One brain hemisphere sleeps at a time.
3. **One eye open**: The opposite eye often stays open.
4. **Staying alert**: It lets dolphins surface and watch for threats.
5. **Birds too**: Some birds sleep this way too.

## Related case files

- [Whale Milk (DD-729)](https://detailenjoyer.com/case/whale-milk/): I linked more about marine mammals
- [Jellies (DD-143)](https://detailenjoyer.com/case/jellies/): I linked more ocean life
- [Humpback Whales (DD-144)](https://detailenjoyer.com/case/humpback-whales/): I paired it with another cetacean

## Reel vs. record

- **Note**: None needed.

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

- Duration: 25.0 s · Published: 2023-12-27
- File: https://detailenjoyer.com/assets/videos/C1XLcyHOa1c.mp4

### Transcript

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!

## Questions & answers

**Q: Why can't dolphins fully shut down?**  
A: They must surface to breathe. _(Source: Write-up · Exhibit A (Voluntary breathing) · Wikipedia: Unihemispheric slow-wave sleep; Wikipedia: Dolphin)_

**Q: What is the sleep called?**  
A: Half the brain at a time. _(Source: Write-up · Exhibit B (Half asleep) · Wikipedia: Unihemispheric slow-wave sleep)_

**Q: What often happens to one eye?**  
A: Opposite the waking half. _(Source: Write-up · Exhibit C (One eye open) · Wikipedia: Unihemispheric slow-wave sleep)_

**Q: What does it let dolphins do?**  
A: While resting. _(Source: Write-up · Exhibit D (Staying alert) · Wikipedia: Unihemispheric slow-wave sleep)_

**Q: Which other animals do it?**  
A: Some other marine mammals too. _(Source: Write-up · Exhibit E (Birds too) · Wikipedia: Unihemispheric slow-wave sleep)_

## Sources

- [Wikipedia: Unihemispheric slow-wave sleep](https://en.wikipedia.org/wiki/Unihemispheric_slow-wave_sleep)
- [Wikipedia: Dolphin](https://en.wikipedia.org/wiki/Dolphin)

## 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/