How Do Dolphins Sleep without Drowning?

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Is it true they fall asleep with one eye open? Answering all these questions and more
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Fast, playful, and intelligent—dolphins certainly are amazing animals! They sure are fun to watch jump and spin out of the water, but have you ever wondered how they get the energy to do all their tricks? Do they sleep? Well, you’ve come to the right place because we’ve compiled everything you’ve ever wanted to know right here. So, let’s dive into that curiosity and learn all about how dolphins sleep.

Things You Should Know

  • A dolphin gets rest using unihemispheric sleep so that they can sleep with one eye open at all times.
  • Dolphins generally need 8 hours of sleep—just like humans do.
  • Being social creatures, dolphins sleep in pods. This way, they can help protect each other throughout the night.
Section 1 of 4:

Do dolphins sleep?

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  1. In order to stay close to the surface so they can breathe, dolphins must stay partially awake while they sleep. How do they do this? Simple—one half of their brain sleeps at a time! This is called unihemispheric sleep and lets a dolphin sleep with “one eye open.” [1]
    • Dolphins alternate which side of their brain is asleep and awake every 2 hours. This way, each side gets an equal amount of rest. [2]
    • Not only is keeping one eye open important for breathing, but it also helps dolphins stay alert for danger.
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Section 2 of 4:

Sleeping & Breathing

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  1. Dolphins may live in the water, but they’re mammals, not fish. This means they need to surface every so often to breathe air in and out of their blowhole. [3] Unlike humans, dolphins don’t have a breathing reflex, so they can’t breathe without thinking about breathing. With one side of their brain being awake at all times, a dolphin is able to surface for air while sleeping.
    • Normally, a dolphin needs to surface for air every 15 to 17 minutes; however, they’ll surface less often when asleep because only one side of their body is awake. [4]
    • Dolphins have to be partially conscious at all times, even when they're sleeping; otherwise, they may drown. [5]
Section 3 of 4:

Where do dolphins sleep?

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  1. These beautiful animals are social creatures, so it’s very rare to see them alone. Not only is sleeping in a pod or group of dolphins fun, but it also provides a layer of protection. If one dolphin spots danger when sleeping, they can wake up the rest of their family and quickly swim away or plan an attack. [6]
    • Dolphins are strategic about what side of their brain sleeps first. A dolphin must be looking inside and outside of the pod at all times, so the pod will communicate with each other to see who’s “on the lookout” for their first shift of rest. Then, they'll switch positions.
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Section 4 of 4:

How long do dolphins sleep?

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  1. However, unlike humans, each side or hemisphere of their brain will sleep in “shifts” so they can stay alert and partly conscious throughout the night. Think of it like a 50/50 split—one side of the brain needs 4 hours of sleep, and then the other side needs 4 hours. [7]
    • These marine mammals can stay awake for at least 15 days if they have to—how amazing is that? [8]

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      References

      1. ↑ https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4948738/
      2. ↑ https://youtu.be/I7yy4H1wiGI?t=78
      3. ↑ https://oceanservice.noaa.gov/facts/dolphin.html
      4. ↑ https://youtu.be/I7yy4H1wiGI?t=86
      5. ↑ https://youtu.be/9-Ds0gA7pMs?t=72
      6. ↑ https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4948738/
      7. ↑ https://www.idw.org/dolphinfacts.htm
      8. ↑ https://journals.plos.org/plosone/article?id=10.1371/journal.pone.0047478

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