One of the strangest looking mammals in Costa Rica is the Brown-throated Three-toed Sloth (Bradypus variegatus). These slow-moving animals have a proportionally small, round head, amazingly long arms, massive claws, and ratty-looking, moth-infested fur that will become covered in green algae during the rainy season. Since they spend almost all of their time hanging in trees, their fur hangs downward from their stomach instead of from their back like other mammals.

We observed this female Brown-throated Three-toed Sloth climbing down to the ground in Manuel Antonio National Park, Costa Rica, which is something that these leaf-eating, tree-dwelling sloths do only infrequently in order to defecate. It was during Costa Rica's rainy season, which is why this sloth's fur was damp and algae-covered.

There are two species of sloth found in Costa Rica, the Brown-throated Three-toed Sloth and Hoffmann's Two-toed Sloth (Choloepus hoffmanni). The two species of sloth are not only distinguished by the number of claws on their front feet, three for the Brown-throated Three-toed Sloth and two for the Hoffmann's Two-toed Sloth, but also by the coloration of their fur. Hoffmann's Two-toed Sloths are a lighter brown with white fur around their face. Brown-throated Three-toed Sloths are grayish brown with a red-brown throat and chest and a dark brown-capped white forehead and trailing, dark brown eye-stripes.

Because of their short-muzzled, rounded head and the delightful curvature of their mouth, Brown-throated Three-toed Sloths have a cheerful "happy face" expression despite the sadly disheveled, ungainly languorousness of their appearance. Brown-throated Three-toed Sloths also have three more cervical vertebrae than other mammals, which amazingly allows them to rotate their head three quarters of the way around, as the above sloth demonstrates. Male Brown-throated Three-toed Sloths have a large, yellow to orange patch on their back, which identifies this one as a female since she lacks such a patch.

Brown-throated Three-toed Sloths are found in the warm, humid tropical forests of Central and South America. With their low body temperatures and slow metabolisms, these sloths need warm temperatures. Slow-moving, arboreal Brown-throated Three-toed Sloths are ungainly on the ground and at great risk from predators there, so they also need dense forests, especially those with lianas and vines that allow them to directly and safely travel from tree to tree.

Brown-throated Three-toed Sloths will also happily use artificial lianas like this wire, but sadly, this habit can result in some of them being electrocuted by power lines. This one was fine though, and she climbed down and crawled off and disappeared into some bushes to do her business in private.