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How do whales and dolphins sleep?

Just like us, whales and dolphins, need sleep to surviveFor animals who spend their entire lives in the water, you may have wondered, how do they sleep without drowning? 

Humans are involuntary breathers because our breathing is automatically controlled by our brainstem. This means that we breathe without thinking about it and breathe automatically even when we fall asleep!  

Whales are voluntary breathers meaning they must think about taking each breath. If they were to fall completely asleep, their brain would rest but they would drown without their brain reminding them to breathe! Instead, they have a fascinating adaptation known as ‘unihemispheric sleep’. To be able to sleep, whales shut down half of their brain at a time. Being partially awake allows them to continue breathing and be aware of their surroundings.  

A humpback whale logging at the surface with cartoon "ZZZ" going away from the whale's blowhole.

Whales will usually stay in place as they sleep near the surface. As they rest, they are switching which hemisphere of the brain is awake. This resting behavior is often called logging because they resemble a log floating at the water’s surface. 

Image credit- Getty Images

Different species have different sleep methods and requirements and the amount of sleep needed can vary greatly between species. For example, researchers believe that sperm whales spend only ~7% of their day sleeping, usually in short naps of 10-15 minutes at a time! This finding makes sperm whales the species that needs the least amount of sleep in the planet! Giraffes are a close second who spend around 8% of their day in slumber.  

Throughout it all, we are still learning about this topic. A great reminder that we still have so much that we don't know when it comes to whales and dolphins!  

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