The Accidental Sloth

“Jen, hurry, there’s something on the bridge!”

I abandoned the lizard I was watching and scuttled to where Piotr Naskrecki was standing. I shone my spotlight on the suspension bridge that spans the Rio Sarapiqui at La Selva Biological Station, in central Costa Rica. It was my first time in the Neotropics and I was eager to see everything. Costa Rica is something of a pilgrimage for tropical biologists, boasting 3-5% of the world’s biodiversity in an area that is only .0003% of the world’s land. In fact, it may have the highest biodiversity of any country.

Two eyes shone back at me like gold coins. The thing was moving, fast, up the twisted steel cables that hold the bridge. I tried to move both quickly and quietly, a difficult thing with clunky rubber boots on my feet, 30 pounds of camera gear on my back, and anticipation clouding my judgment. So I squeaked, clanked, and panted toward it.

Somehow, the thing detected us and started moving faster, the two gold coins bouncing up the cable.

It sprang within range of my beam. “It’s a kinkajou!”

The kinkajou (Potos flavus) is related to raccoons but looks more like a cross between a monkey and a teddy bear. In addition to having one of the coolest names in the animal kingdom, kinkajous are important pollinators and seed dispersers with 5-inch tongues that they use to harvest fruits and nectar.

“I have to get a video.” Piotr said with conviction. He heaved his elephantine camera bag onto the bridge and started rummaging through it as I watched the kinkajou scurry up the cable. As soon as it was above Piotr, it paused, turned, and lifted its tail in his direction. Was that a mischievous gleam in its eye or just the reflection of my spotlight? “Uh oh,” I thought, in the split second before it happened.

A huge diarrheal turd landed splat on the bridge, inches from Piotr’s camera bag. The kinkajou then released the longest stream of urine I’ve ever seen, stretching from its perch 10 meters above us to the bridge, where it rained, and rained, and rained until it trickled over to Piotr’s bag.

Piotr's video of the kinkajou. Worth being shat on for...?

“I guess it doesn’t like you.” I stepped over the urine puddle to follow the animal along the cable. Its arms swung with a boxer’s hook at every step, its body sleek and undulating. As it was nearing the bridge’s tower, it passed inches below a big brown termite nest.

Or was it a termite nest? It looked awfully hairy.

“SLOTH!” I nearly yelled, giddy with excitement. Even 10m up, its algae-covered fur shone green. I couldn’t believe it – these two animals that had previously existed for me only in books were practically spooning. 

I reluctantly let the kinkajou escape into the darkness and instead watched the sloth. Big surprise, turns out they don’t do much. In Spanish, sloths are called “oso perezoso”, or the lazy bear. In English, of course, they’re named after one of the seven deadly sins.

My first sloth, doing absolutely nothing. Photo by Piotr Naskrecki.

But they have a good excuse for their perceived laziness – their diet of leaves (for three-toed sloths; two-toed sloths also eat  fruits and flowers) is incredibly poor in nutritional content and difficult to digest. Each meal spends four whole weeks in a sloth’s multi-chambered digestive system, broken down with the help of symbiotic bacteria, before it’s voided. And that process, too, is a mission – sloths climb down from the trees once a week to release a one-kilogram (two pound) poop along with an entire liter of urine. A sloth can lose up to two-thirds of its body weight in a single trip to the bathroom (think about it). And like any good outdoorsman, they dig a hole and cover it when they’re done. Since half of all sloth deaths are estimated to occur during their weekly bathroom break, there must be a good reason for shitting among the jaguars. But scientists still don’t know what that reason is.

A three-toed sloth during a bathroom break on the forest floor. Photo by Piotr Naskrecki.

As a consequence of their slow digestion and poor diet, they live nearly their whole lives in energy-conservation mode. They have slow metabolism and low body temperature. They move slowly, and only if they have to, and take frequent naps even during their active period (daytime for three-toed, nighttime for two-toed). That’s strategy, not laziness. If a sloth is threatened it can swipe with its two or three sickle-claws nearly as fast as a cat.

 “Two-toed” and “three-toed” is a misnomer. The Spanish name, “dos dedos” and “tres dedos” – two- and three-fingered – is more accurate. These sloths all have the same number of toes (three) and it’s only the number of digits on their hands that changes. My first sloth was a two-toed (Choloepus hoffmanni, one of two two-toed species in the neotropics), and pretty adorable even at 10 meters in the dark.

It wasn’t quite as adorable, though, as this baby two-toed sloth I saw at the sloth rescue two days later. Sloths throughout the Neotropics are threatened by habitat destruction and other human interference. Power lines, for example, pose a huge problem for sloths – if they grab a live wire in one of the ubiquitous jungle downpours, they may end up with a fried limb or worse. And their less-than-speedy pace often puts them at the unlucky end of speeding cars.

A baby orphan two-toed sloth hangs onto its keeper's shoulder.

Fortunately, Costa Rica is doing a spectacular job of conserving its natural heritage. About 25% of its land is protected, and almost 50% of its land is still forested. In addition, a number of animal rescues and sanctuaries operate throughout the country. In Costa Rica, at least for now, sloths can keep leisurely munching leaves in the canopy.