Lazy Animals – The Sloth

The living sloths (bicho-perguiça in Portuguese, meaning lazy animal) comprise six species of medium-sized mammals that live in Central and South America. Most scientists call the sloth suborder Folivora, while some call it Phyllophaga. Both names mean “leaf-eaters”; the first is derived from Latin, the second from ancient Greek. Tribal names include Ritto, Rit and Ridette, mostly forms of the word “sleep”, “eat” and “dirty” from Tagaeri tribe of Huaorani (Ecuador).

Ecology

The living sloths are omnivores. They may eat insects, small lizards, and carrion, but their diet consists mostly of buds, tender shoots, and leaves, mainly of Cecropia trees. They have made extraordinary adaptations to an arboreal (tree-living) browsing lifestyle. Leaves, their main food source, provide very little energy or nutrition and do not digest easily: sloths have very large, specialized, slow-acting stomachs with multiple compartments in which symbiotic bacteria break down the tough leaves. As much as two-thirds of a well-fed sloth’s body-weight consists of the contents of its stomach, and the digestive process can take a month or more to complete. These facts tell us that sloths are not only slow-moving, but slow in most other aspects as well.

Although unable to survive outside the tropical rainforests of South and Central America, within that environment sloths are outstandingly successful creatures: they can account for as much as half the total energy consumption and two-thirds of the total terrestrial mammalian biomass in some areas. Of the six living species, only one, the Maned Three-toed Sloth, has a classification of “endangered” at present. The ongoing destruction of South America’s forests, however, may soon prove a threat to other sloth species.

Physiology

Sloth fur exhibits specialized functions: the outer hairs grow in a direction opposite from that of other mammals. In most mammals, hairs grow toward the extremities, but because sloths spend so much time with their legs above their bodies, their hairs grow away from the extremities in order to provide protection from the elements while the sloth hangs upside down. In moist conditions, the fur hosts two species of symbiotic cyanobacteria, which provide camouflage. The bacteria provide nutrients to the sloth when licked during grooming. Sloth fur is also host to algae; this algae colors the coat green and acts as camoflauge. Because of this algae, sloth fur is a small ecosystem of its own, hosting many species of non-parasitic insects.

Sloths move only when necessary and even then very slowly: they have about half as much muscle tissue as other animals of similar weight. They can move at a marginally higher speed if they are in immediate danger from a predator (4.5 m or 15 feet per minute), but they burn large amounts of energy doing so. 

They are particularly partial to nesting in the crowns of palm trees where they can camouflage as coconuts. They go to the ground to urinate and defecate about once a week. They go to the same spot each time and are vulnerable while doing so. The reason for this risky behaviour is unknown.

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