“Sloths move slowly because their leafy diet gives them very little energy.”
Brown-throated sloths spend most of their lives hanging beneath branches in Central and South American rainforests. A low-energy leaf diet favors slow movement, long rest, and a specialized coat whose grooves can support algae in humid conditions.
By An Nguyen · Published · Updated
Bradypus variegatus Pilosa Bradypodidae
Measured against the 176 species profiled on this site. Each figure is converted to one unit system from the published range on the page, so the ranks are computed, not quoted.
| Measure | This species | Rank here | Exceeds |
|---|---|---|---|
| Body mass | 4.5 kg | #113 of 176#80 of 90 Mammalia | 36% |
| Body length | 68.6 cm | #115 of 176#75 of 90 Mammalia | 35% |
| Lifespan in the wild | 30 yr | #44 of 169#20 of 85 Mammalia | 74% |
Closest in body mass
Ranks use the upper end of each published adult range, so they compare typical large adults rather than records, and metrics with no published number are left out rather than estimated. The full table is downloadable from the species dataset, and any two species can be put side by side in the comparison tool.
Browse photographs of brown-throated sloth across habitat, behavior, anatomy, and life stages.
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Core article
A closer look at habitat, diet, behavior, reproduction, and conservation.
The brown-throated three-toed sloth (Bradypus variegatus) lives high in the canopy of Neotropical rainforest and moves at a famously slow pace. That slowness is energy conservation rather than laziness: by holding its metabolic rate low and hanging upside down for most of its life, it survives on a low-calorie diet of toxic leaves that would starve most other mammals. It is one of the most successful canopy dwellers in the Americas.
A mature brown-throated sloth is small, 18 to 27 inches and 6 to 10 pounds, with a body entirely built for hanging: forelimbs longer than hindlimbs, and both feet ending in three sickle-shaped claws up to 4 inches long that hook over branches like meat hooks so the animal can hang for hours with no muscular effort. Its fur grows the "wrong" way — from belly toward back — so rainforest downpours roll off, and grooved hair shafts host symbiotic green algae that camouflage the sloth and even supply some nutrients. Internally it is radically slowed: a basal metabolic rate less than half what its size predicts, a body temperature that drops at night to save energy, and two extra neck vertebrae (nine instead of seven) that let it rotate its head 270 degrees. It belongs to the three-toed sloth family Bradypodidae, within the ancient American lineage Xenarthra that also holds anteaters and armadillos; the small tree sloths are dwarf survivors of once-elephant-sized ground sloths.
The brown-throated sloth has the widest range of any sloth, from Honduras and Nicaragua through Panama, Colombia, Venezuela, and Ecuador across the Amazon basin to northern Argentina. It is a strict arboreal specialist of dense lowland rainforest, riverside gallery forest, and mature secondary forest, and it needs a connected canopy: because its movement on the ground is so labored and vulnerable, a gap that forces it down puts it in immediate danger. It especially favours Cecropia trees, which offer both food and open branches for basking.
Bradypus variegatus is an obligate leaf-eater (folivore), and rainforest leaves are a brutal diet — tough, fibrous, laced with toxins like tannins, and very low in calories. To cope it has a massive multi-chambered, ruminant-like stomach that can be up to 30% of its body weight when full, packed with symbiotic bacteria that slowly ferment cellulose; a single meal can take 16 to 30 days to pass through. Because that diet yields so little energy, its main feeding strategy is conservation itself — moving slowly to keep its metabolism low and selecting younger, more tender, less toxic leaves and buds.
Brown-throated sloths are strictly solitary, meeting only briefly to mate, and are generally silent apart from high whistle-like calls in distress or courtship. Their strangest habit is bathroom-related: despite living in the high canopy, a sloth descends to the forest floor about once a week to defecate, digging a small hole at the base of its tree with its stubby tail. Biologists tie this dangerous, energy-costly trip to a mutualism with the sloth moth, which lays eggs in the fresh dung; the larvae mature and fly up to colonize the sloth's fur, and the moths in turn help fertilize the camouflaging algae the sloth relies on.
Reproduction is slow and deliberate. A female in estrus signals with loud, high calls that carry through the canopy, and males navigate the branches to reach her. After about six months' gestation she gives birth hanging upside down to a single, surprisingly well-developed infant — furred, eyes open, and able to grip her belly fur at once. It clings there for the first 4 to 6 months, sampling the specific leaves she eats to acquire the gut flora it needs to digest them, weans around five months, and may stay in her territory up to a year before dispersing. Wild brown-throated sloths generally live 20 to 30 years.
The brown-throated three-toed sloth is Least Concern, its global population stable thanks to a huge range across the Amazon and Central America, and it is common in many protected areas. But it faces severe local threats: deforestation for agriculture, ranching, and logging fragments the canopy, forcing sloths to crawl across the ground where they are nearly defenseless against feral dogs, vehicles on new logging roads, and jaguars. They are also victims of the illegal wildlife trade, with poachers tearing infants from mothers for the pet trade and "sloth selfie" tourist traps.
Kingdom
Animalia
Phylum
Chordata
Class
Order
Pilosa
Family
Bradypodidae
Genus
Bradypus
Species
B. variegatus
Sloths move slowly because their leafy diet gives them very little energy.
Three-toed sloths have three claws on each front and hind foot.
Sloths spend most of their lives hanging upside down in trees.
Green algae sometimes grows in sloth fur and helps them blend in.
Sloths descend to the ground only about once a week.
Baby sloths cling to their mothers for months while learning to climb.
Select a question to reveal the answer.
Brown-throated sloths live in tropical rainforests from Honduras through northern South America.
Sloths are herbivores that eat leaves, buds, and tender shoots from rainforest trees.
Leaves are low in calories, so sloths move slowly and rest often to save energy.
Long curved claws hook over branches so sloths can hang without using much muscle strength.
Brown-throated sloths are listed as Least Concern, but habitat loss can harm local populations.
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