There is something almost unbelievable about the sight of it. A pod of sperm whales, some of the largest predators on Earth, hanging upright in the water like a stand of enormous gray pillars. Perfectly still. Fast asleep.
Which animal sleeps vertically?
The sperm whale is the best-documented vertical sleeper. Pods rest head-up or head-down just below the surface, in naps that average about 12 minutes and can stretch past half an hour. Other whales, such as humpbacks and belugas, tend to rest lying flat at the surface instead.
We know this thanks to a 2008 study in Current Biology. Researchers led by Patrick Miller attached tags to 59 sperm whales and found that 31 of them made what the team called drift dives, sinking gently and then hanging motionless. Those rests took up about 7 percent of all the time recorded. Each one lasted anywhere from under a minute to more than half an hour, with an average of 12.7 minutes. Some whales floated head-up about 9 meters down, and others hung head-down a little deeper.
The pictures that made the behavior famous came much later. In January 2017, Swiss photographer Franco Banfi was freediving off Dominica when he found himself among a sleeping pod, and his photos traveled around the world. The images here come via Discovery, and the video below puts a diver right alongside a resting group.
Sperm whales spend most of their lives hunting squid in the deep, so these short naps near the surface are their chance to recharge. And there is a lot to recharge. The sperm whale has the largest brain of any animal on Earth, more than five times heavier than ours.
Since then: In July 2026, a team from the University of St Andrews and the University of Neuchâtel published a study in the Journal of Experimental Biology explaining how the whales stay put. Their huge heads are naturally buoyant, so resting whales quietly release bubbles of air to keep from drifting up toward the surface. Every resting whale the team tracked off Norway did it!
Images via Discovery.
If you love a close encounter, don’t miss what it is like to come face to face with a humpback whale, or our tribute to David Attenborough at 100. There is more from the deep in our nature stories.
