How Do Whales Sleep? They're Always Half Awake (Literally)

It’s a question that puzzles many ocean lovers: How do whales sleep without drowning? Unlike us, whales are voluntary breathers, meaning they have to consciously come up for their next breath. That makes their sleeping habits pretty unique among marine mammals.

Here’s how whales and dolphins sleep while staying safe and getting just enough rest.

Contents

Unihemispheric Sleep: Resting Half the Brain
Logging, aka Day Sleeping
Short Sleep Sessions
How Do Dolphins Sleep?
Adapted for a Lifetime at Sea

Unihemispheric Sleep: Resting Half the Brain

The trick to how whales sleep lies in unihemispheric sleep — a process where only one half of the brain rests at a time while the other half remains alert.

This allows the animal to remain conscious, surface for air and keep an eye out for potential predators.

This specialized sleeping pattern is common among marine animals like bottlenose dolphins and humpback whales. While one brain hemisphere sleeps, the whale can swim slowly, maintain swimming muscles activity and make that crucial trip to the water’s surface.

Logging, aka Day Sleeping

Humpback whale asleep — Whales have unique sleeping patterns that allow them to stay underwater even though they require air to live. Moelyn Photos / Getty Images

Many whale species, including sperm whales, engage in a behavior called logging.

During logging, the whales float near the surface, motionless, resembling logs. This often occurs during the day, a behavior known as day sleeping. In this state, they conserve energy and still get the rest they need.

Young whales and calves usually sleep alongside their mothers, sometimes aided by the mother’s slow, rhythmic swimming. In larger pods, whales may synchronize their rest periods for safety.

Short Sleep Sessions

Whales and dolphins don’t get the long hours of deep sleep we enjoy. Instead, they may rest for short intervals, often up to two hours at a time, ensuring they regularly return to the surface for oxygen.

Their blood, rich in red blood cells, helps carry more oxygen and supports these short rest cycles.

How Do Dolphins Sleep?

Dolphins sleep similarly to whales. Bottlenose dolphins, for example, use unihemispheric sleep and often rest while slowly swimming or floating.

Like whales, they’re voluntary breathers, and their rest strategy ensures they never miss a breath.

Adapted for a Lifetime at Sea

Humpback Whale — Look at this majestic humpback whale. Vincent Pommeyrol / Getty Images

Because whales and dolphins spend their entire lives in the ocean, their resting behavior is finely tuned to balance safety, movement and oxygen intake.

From the surface calm of a log-floating humpback to the synchronized sleep of a pod, whales’ sleep strategies are a necessity of marine adaptation.

We created this article in conjunction with AI technology, then made sure it was fact-checked and edited by a HowStuffWorks editor.