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The sloth (Bradypus sp.) is a strong contender for the title of Weirdest Amazon Animal. From a distance, it might be mistaken for a giant fruit or an ants' nest, especially because most of the time, it remains motionless; the sloth attaches to a chosen resting spot and sleeps for four-fifths of its life (seems like some teenagers I know!). The sloth's coloration is effective camouflage for an animal that wants to look like a nest or fruit. It is covered with thick unkempt gray-green to brown fur which afford some camouflage among the rainforest canopy tree crowns. During the one fifth of the time when it is actually active, the sloth hangs upside down, from long gangly limbs equipped with two to three long curved claws; its only defense. It moves through the trees with slow, measured movements, but is actually an adept swimmer, and will drop into water if possible to escape predators, primarily the harpy eagle. The sloth has forward-facing eyes and a small rounded snout, conferring upon it a primate-like appearance. But the sloth is not related to the monkeys, and in fact lacks a tail (possessed by most primates). It belongs to a uniquely South American group, the edentates, which inludes armadillos and anteaters, and so-called because of their primitive dentition. The sloth is no exception. Although the sloth is a vegetarian, its teeth are poorly adapted to the task, being peg-like stumps. (Most mammals have teeth which are highly differentiated to serve specific purposes such as grasping, shearing and crushing.)

The brown throated three-toed sloth (B. variegatus) is the commonest and most widespread of four species found in Amazonia (a fifth species, the maned three-toed sloth, B. torquatus, is found only in the Atlantic rainforest on Brazil's southeast coast). It ranges throughout the lowland rainforest from northern Argentina and Bolivia to western Venezuela and Central America. East of the Rio Negro and north of the Amazon River, it is replaced by the pale-throated three-toed sloth (B. tridactylus). Sloths spend virtually all their lives high in the forest canopy, preferring trees with high crowns bathed in sunlight. On the ground, the sloth can barely walk and practically helpless. However, to escape arboreal predators it will drop into water and swim away. Its ability to swim also makes the sloth quite able to migrate around lowland forest areas where rivers thread their way among the trees. High in the canopy where the sloth has slept overnight, it warms itself in the morning, and when awake, slowly moves around to look for food. (I bet that sounds like someone you know! :) They seem to reach their highest population numbers in dense secondary forest (rather than primary rainforest). These habitats have a high proportion of new leaves favored by sloths and the main predator, the harpy eagle is quite rare in secondary forest.

Sloths are strictly herbivorous, and quite particular about what they eat—leaves and only leaves. They feed on many species of trees, but also avoid many. Among their favorite food trees is cercropia (see photo), a common riverside tree. This tree is protected from most herbivores by vicious stinging ants. The sloth, however, seems unperturbed by the ravaging insects. (Perhaps its silky fur makes it hard for the ants to attack, or maybe there are oils in the sloth's skin that inhibit attack. Sloths usually feed high in the canopy so stands of cercropia, which is relative low-growing, are ideal to spot these creatures. Uniquely for an arboreal animal, the sloth descends to the ground to defecate! The reason is not entirely clear, but the act is performed only once a week. They climb down the tree, to the base, and dig a hole with their short stubby tail. After defecation, the tail is used to fill the hole, presumably to prevent the odor from alerting nearby predators.

Due to their inaccesibility, sloths do not make great subjects for scientific study. So not much is known about the details of their reproduction. After mating, and gestation of about six months, a single young is born. For six to nine months, the offspring is carried by the mother. The baby sloth clings to her belly (riding on top) and when strong enough ventures off to climb branches without her help. From its mother, the young sloth learns the best food plants and how to move around within her home range. A strong bond between the mother and baby help the sloth get started in its complex arboreal world. It stays in contact with the mother by calling, even after it has left her home range.

Sloths are in pretty good shape from a conservation stand-point. Their generalist diet means they can adapt to reforested areas, and they can thrive in city gardens and parks where they are released after being captured by people. Sloths are the most abundant large mammal in the canopy, comprising up to a third of the biomass. It's the mammal most likely to be seen in the wild by visitors to the Amazon. Although widely hunted by people it is hard to see, and manages to survive heavy hunting pressure. When its habitat is destroyed by clear-cutting or flooding due to dams, huge numbers are found. The destruction of habitat remains the greatest threat to sloth populations.


The Sloth Web Site
Enchanted Learning: All About Sloths
Wikipedia: Sloth Sloth—The mammal
The Biogeography of the Brown-throated Three-toed sloth (Bradypus variegatus) facts about two & three-toed sloths
Sloth World : An online bibliography and database of sloth papers
Animal Diversity Web: "Bradypus variegatus"
TigerHomes: Three-Toed Sloth
Brazilian Journal of Biology: Social behavior between mothers x young of sloths Bradypus variegatus Schinz, 1825 (Xenarthra: Bradypodidae)
International Journal of Morphology: ANATOMICAL ASPECTS OF THE PLACENTA OF THE SLOTH, Bradypus variegatus, SCHINZ, 1825.
BioOne: Sloths in the Diet of a Harpy Eagle Nestling in Eastern Amazon
Mammal Directory: Sloths
The Life of the Sloth: Final Draft
Mongabay: Educational resources on Three-Toed Sloth

Mainly photos
Alternet: A two-toed sloth hangs from a tree in Machia Park in the Bolivian Amazon
Digimorph: sloth skull
Dr. Zoltan Takacs: Three-toed sloth (Bradypus variegatus), Amazonas, Brazil
University of Alaska: Bradypus variegatus
Ecology Photographic: Bradypus-1

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