Sloths are known for their unhurried pace, sleepy eyes and gentle way of life. But under all that calm is a party trick almost nobody expects. A sloth can hold its breath for up to 40 minutes. Yes, really!
How long can a sloth hold its breath?
Up to about 40 minutes, by slowing its heart to roughly a third of its usual rate. A bottlenose dolphin’s longest dives last 10 to 15 minutes, and most of its dives are over in well under a minute.
To put that in perspective, most of us start to feel light-headed after a minute or two. Dolphins, some of the most gifted swimmers on the planet, usually dive for just 20 to 40 seconds at a time. The Wild Dolphin Project puts their maximum at 10 to 15 minutes, and the longest it knows of was a tagged dolphin off Bermuda in 2016 that stayed under for 14. The humble sloth leaves both of us behind.
One honest note. The 40-minute figure comes from people who work closely with sloths and gets repeated everywhere, but we couldn’t find a published study that actually timed one. The broad shape of it holds up, though, and the reason why is the interesting part.
So how do they do it?
Everything about a sloth runs slow. The Smithsonian’s National Zoo notes that their metabolism runs at 40 to 45 percent of what you would expect for an animal their size. Underwater, their heart slows even further, to around a third of its normal pace, so a single breath stretches a very long way. A body that barely spends energy doesn’t need much air to keep going.
They don’t need to surface for air often, which is handy when you spend your life in trees hanging over rivers and rain-soaked forests.
Why would a sloth need to hold its breath?
Sloths aren’t aquatic animals, but they are surprisingly strong swimmers. The National Zoo describes a kind of doggy paddle, and National Geographic notes they are often seen crossing rivers with ease. In the water, their long arms and buoyant bodies make them far more graceful than they ever look in a tree.
That swimmer is a pygmy three-toed sloth, filmed for the BBC’s Planet Earth II as it crossed a mangrove channel in search of a mate. It lives in only one place on Earth, Isla Escudo de Veraguas, a small island about 17 kilometers off Panama’s Caribbean coast. A 2012 survey counted just 79 of them, and the species is listed as Critically Endangered. The sloth in our cover photo is one of them.
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The BBC clip below shows more of these tree-dwellers at their most surprising.
The more we learn about sloths, the stranger and better adapted they turn out to be. Their fur grows algae that helps them blend into the canopy, and researchers think that algae may even be a snack. They digest upside down. And now it turns out they can outlast a dolphin underwater. For more of nature’s quiet survival tricks, see our visual guide to the most extraordinary defense mechanisms in the animal kingdom, or wander through the rest of our nature stories.
