Slothful Camouflage – Rainforest Adventures Costa Rica Atlantic, Guápiles, Limón Province, Costa Rica

If you look carefully at the centre of this picture, you will see a three-toed sloth hanging from a branch at the top of this tree. (It's more visible at full-screen size against a black backgroud.)

Among the greatest mysteries of the tropical rainforest are the pooping habits of sloths. Really. Those furry, slow-moving tree dwellers almost never descend from the safety of the tree tops – except for once a week, when nature calls. It’s a dangerous and often lethal potty break. On the forest floor, they are spectacularly vulnerable to predators, and the question biologists have been asking for years is, why descend at all? What possible benefit could make this life-or-death journey better for the sloth than simply cutting loose, as it were, from the safety of a tree?

The reason for this risky behaviour is unknown, although some believe it is to avoid making noise while defecating from up high that would attract predators. Consistent with this, they reportedly relieve themselves from their branches during storms in the rainy season. Another possible explanation is that the middens provide the sloths with one of their few methods of finding one another for breeding purposes, since their sense of smell is far more acute than their eyesight or hearing. Still other recent studies have suggested that it might be relevant for maintaining the ecosystem in the sloths’ fur. Individual sloths tend to spend the bulk of their time feeding on a single "modal" tree; by burying their excreta near the trunk of that tree, they may help nourish it. Recently there has been some speculation that sloths go to the ground to defecate because of their mutually beneficial relationships with moths. While the sloth defecates, female moths that otherwise live on a sloth will get off and immediately lay their eggs directly on the fecal matter, on which the larvae survive until they mature to adulthood and are able to fly onto sloths. Incidentally, it appears that sloths benefit from their relationship with moths because the moths are responsible for fertilizing algae on the sloth, which provides them with nutrients.