Plants and Animals

Sloths aren’t lazy – their slowness is a survival skill

The ConversationConventional wisdom has it that sloths are simple, lazy creatures that do very little other than sleep all day. Even the very name “sloth” in most languages translates as some version of “lazy”. It seems astonishing that such an animal survives in the wild at all.

In 1749, French naturalist Georges Buffon was the first to describe the creature in his encyclopedia of life sciences, saying:

Slowness, habitual pain, and stupidity are the results of this strange and bungled conformation. These sloths are the lowest form of existence. One more defect would have made their lives impossible.

Given such a precedent, it is of little surprise that sloths are subject to such profound speculation and misinterpretation, ranging from the benign – that they sleep all day – to the creative anecdotes I regularly hear, such as: “Sloths are so stupid that they mistake their own arm for a tree branch”.

The truth is that sloths are incredibly slow movers, but for a very simple reason: survival. The fact that slow sloths have been on this planet for almost 64m years shows that they have a winning strategy. But in order to understand exactly what it is that makes them such slow movers, and why this works so well, we have to look at the biology of these unusual animals in more detail.

Plenty of time to hang around for this little sloth. Suzi Eszterhas, www.suzieszterhas.com, Author provided

Three-toed sloths are indeed the slowest-moving mammals on the planet, but exactly how slow is slow? At the world’s only sloth sanctuary in Costa Rica, we have been monitoring the movement and activity patterns of wild sloths using small data loggers combined with tracking devices inside specially built “sloth backpacks”. We’ve found that, contrary to popular belief, sloths don’t actually spend inordinate amounts of time sleeping; they sleep for just eight to ten hours a day in the wild. They do move, but very slowly and always at the same, almost measured, pace.

Moving slowly unequivocally requires less energy than moving fast, and it is this principal that underlies the sloths’ unusual ecology.

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