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Bradypus variegatus


Both the Brown-throated Three-toed Sloth and Hoffman's Two-toed Sloth have very strange bathroom habits for animals considered canopy species. Instead of dropping their waste from the treetops, which monkeys seem more than happy to do (throwing it on occasions), sloths make a bizarre weekly pilgrimage down to the ground to take care of business on "terra firma".

Upon arrival Three-toed Sloths dig a hole with their stubby tail and lay their urine and droppings in it. Brown-throated Three-toed Sloth - Bradypus variegatus

They may loose up to one third of their body weight in urine and feces during one of these trips! The hole is then covered up and the sloth makes its journey back into the treetops. Two-toed Sloths don't have a tail, so they just lay their droppings on the ground and begin their ascend to the treetops when they are finished.

Until recently it was a mystery why they behave this way, since it would seem that by descending to defecate they are putting themselves at great risk.

Researchers have found that there is a very good reason they descend to the ground to defecate.

It turns out that Sloth's fur may be home to up to 100 moths and up to 1000 beetles! When Sloths descend to the ground to defecate these insect make their way to the dung and lay their eggs in it. Their larvae develops in the dung and when they become adult insects they fly up into the treetops and find another sloth.

The Sloth Moth, Cryptoses choloepi, exists nowhere else in nature except in association with Sloths and scientists believe this relationship has been ongoing for millions of years. Several Sloth Moths are visible on the back of the Sloth in photograph featured here.

A really close inspection of the Sloth's fur will reveal many small grooves which cover each one of the hairs on which algae grows. The algae provides Sloths with some camouflage, making their fur look green. It also helps hide their scent from predators.

But the algae provides Sloths with an even more important service. Researchers have recently found that Sloths graze on their algal gardens from which they obtain easily digestible lipids and carbohydrates. It is literally a nutritional supplement for the Sloth!! It is a vitally important nutritional supplement because Sloth's normally leafy diet is very difficult to digest and may take up to 3 weeks to pass from one end to the other. 

The algae thrives on the decaying bodies and the feces of the insects along with oils from the sloth's skin. Scientists estimate that the moths also introduce inorganic nitrogen and phosphorus (possibly from the Sloth feces in which they develop as larvae) into the Sloth's fur which helps foment the algal garden. This fecal matter along with the dead insects and insect feces are further broken down by over 80 different species of fungi also present on the Sloth's fur, making the nutrients more accessible to the algae. So, the more insects the sloth has living in its fur, the more algae the Sloth will have growing on its hair which will in turn enhance the its nutrition!!!  

In essence, these very different organisms are linked in a symbiotic relationship which benefits them all. The Sloth contributes by providing a home for them in its fur and venturing down to the ground to lay a nice big pile of dung on which the insects can lay their eggs.

So as not to attract to much attention, these trips often take place under cover of the night. This allows us night owls a rare close up view of an animal normally seen high in the trees through spotting scopes and binoculars.

Brown-throated Three-toed Sloth - Bradypus variegatus

Every so often on the Night Tour, we are fortunate enough to cross paths with one of these canopy dwellers at eye level and find ourselves face to face with a sloth. These encounters are wonderful experiences and immediately strike wonder into every member of the group, guides included.

Sloths, especially Three-toed Sloths, emit a certain tranquil vibe that is hard to match. Often, when we cross paths on the trail, they don't seem to mind our company too much and simply carry on with whatever was occupying them before we arrived. There is something very heartwarming and reassuring in their sluggish stride and gentle smile.

Like everything in nature, Sloths are built to perfection for life in their environment: the forest canopy. Their hands and feet have evolved into hook like appendages from which they hang from tree limbs effortlessly. Their perceived laziness is more aptly described as energy efficiency at its finest. Because the Three-toed Sloth's diet is made up almost entirely of leaves, which contain hard to obtain calories, a sloth's activity level is necessarily low.

Everything about the sloth, even down to its hair, is designed to minimize energy consumption. Its thick fur provides insulation and prevents heat dissipation. The Sloth's hair is parted along their belly pointing downward, towards it's back. This way, rain will more easily run off its hair keeping the skin warm and dry.

Another way Sloths conserve energy, which is quite remarkable for a mammal, is by entering a nightly hibernation. Instead of investing valuable energy in maintaining a steady body temperature, on cold nights Sloths allow their body temperature to drop as much as twelve degrees centigrade! Other mammals, including humans, would find themselves fighting for their lives with even a five degree drop in temperature.

Brown-throated Three-toed Sloth - Bradypus variegatus

In the morning, they make their way to the treetops and sunbathe in order to raise their body temperature to the levels required for them to resume their activity.

Traditionally, this has made Sloths an easy meal for one of their main predators, the Harpy Eagle. These are the world's heaviest eagles and females may stand over a meter tall weighing up to 7.5 kilograms. An average Three-toed Sloth only weighs about 4 kilos.

When hunting, Harpies glide in or below the forest canopy, making short flights through the treetops, stopping to look and listen for prey. Once they have located a target, including even the most camouflaged sloth, there is little hope for it.

Attacks are swift and sudden and usually come from the side or below. With talons as long as bear claws and wrists as thick as those of an adult man, the Harpy Eagle pounces on the helpless sloth and rips it from the tree despite its strong grip.

Research at one Harpy Eagle nest site revealed that the parent birds brought 26 sloths back to the nest for their hatchlings to feed on during a 10 month period! Although Sloths make up a large part of the Harpy Eagle's diet, other prey items may also include monkeys, porcupines, opossums, coatimundis, and other large mammals.

Despite popular claims regarding their incredibly slow movements, Sloths can certainly move when they need to. We have often watched Three-toed Sloths move all the way across our garden, if not swiftly certainly steadily, and most individuals we encounter on The Night Tour are usually nowhere to be seen within a few minutes. Two-toed Sloths can be surprisingly quick, much more so than Three-toed Sloths.

One night, during a Night Tour, we saw two female Sloths fighting for feeding rights in a Cecropia tree. What a scene! One female would swing her arm back behind her head, in a futile attempt to gain momentum, and then hurl it towards her rival. Meanwhile, the other female would begin to lean backwards way ahead of time, anticipating the strike. They went on like this for several minutes until we finally left them to sort themselves out in private.

It was a little bizarre, resembling the scene in "The Matrix" where Keanu Reeves is dodging bullets in slow-motion. Brown-throated Three-toed Sloth - Bradypus variegatus

After the tour, as we were heading home, we saw one of the females retreating down the trunk of the tree. It was then that we noticed she had been cradling her baby throughout the whole ordeal.

Three-toed Sloths are active an average of 10 hours per day, about three more hours than their Two-toed counterparts. This activity level is not uncommon for animals that only need to feed sporadically. They get all the moisture they require from their leafy meals and have no need to seek out drinking water.

Still, Sloths cling to their reputation as lazy and static creatures. Adrian Forsyth's captivating book Portraits of the Rainforest tells of a myth by The Bororo Tribe of South America that may help explain, and perhaps excuse, their laid back demeanor.

"Long ago, the sloth was not easygoing. He moved rapidly through the forest and had a nasty, greedy temperament. One day, the Almighty decided to descend to Earth. He waited four weeks until the hole in the sky known as the moon was fully open, and then He climbed down on a liana.

On His arrival, He went to drink at a water hole. A group of animals - a tapir, a hare, a jaguar, an anteater and others - all stepped aside so that He could drink first. All but the sloth. The sloth pushed ahead and drank greedily and at great length. This, of course, angered the Almighty One, and He announced to the sloth that in punishment, He would cast a spell.

The terrified sloth expected death. But the Almighty just breathed on him, snuffing out forever his greed and thirst. With great relief, the sloth smiled, and since then, he has never had another drink and has been as easygoing as they get."



Avila, D.  2007  Ni Osos..., Ni Perezosos!  Editorial INBio

Ewing, J.  2005  Monkeys are Made of Chocolate  PixyJack Press

Forsyth, A.  1990  Portraits of the Rainforest  Camden House Publishing

Henderson, C.  2002  Field Guide to the Wildlife of Costa Rica  University of Texas Press

Stiles, G. & Skutch, A.  1989  A Guide to the Birds of Costa Rica  Cornell University Press

Wainwright, M.  2002  The Natural History of Costa Rican Mammals  Zona Tropical

Jonathan N. Pauli, Jorge E. Mendoza, Shawn A. Steffan, Cayelan C. Carey, Paul J. Weimer, M. Zachariah Peery, January 22, 2014
Proc. R. Soc. B 2014 281 20133006



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