Brown-throated Sloth

Bradypus variegatus. Borba, Rio Madeira, River Amazon, Brazil. 1830.

When naturalist Johann Natterer found this sloth during the Austrian expedition to Brazil and sent it to the NHM in 1830, it was a true rarity in Europe.

ENERGY SAVER
Sloths are considered contemptible creatures because of their slow, ponderous movement, and not only by many Europeans. In their native country of South America they have an extremely bad reputation – wrongly so, because their behavior can be explained biologically.
Sloths eat almost exclusively leaves. It takes a long time for this fibrous, low-nutrient diet to be broken down in the digestive tract with the help of bacteria. All the sloth’s other bodily functions are correspondingly slow. Of all mammals, sloths have the lowest rate of metabolism relative to the size of their bodies. At around 34° C, their body temperature is also very low and can drop another ten degrees during sleep.
A sloth therefore has very little energy to use for movement. It swings hand over hand from branch to branch at a speed of no more than four meters a minute, hooking into the tree bark with its curved claws, which can be up to 7.5 centimeters long. In between they remain almost motionless amidst the thick foliage. This behavior makes sloths almost invisible to their enemies. During the rainy season, tiny algae that give the sloth’s fur a greenish tinge which adds to its camouflage. Sloths only leave their treetop realm only about every eight days, when they climb down to the ground to defecate and urinate.
Molecular biological analyses have shown that despite their similar appearance, two-toed and three-toes sloths are not very closely related. The two families probably diverged around 35 million years ago.