Sloth

Group of tree dwelling mammals noted for slowness
the Central and South American mammal

Automatic taxobox
| name = Sloths
| fossil range = Early Oligocene to Holocene
| image = Bicho preguiça 3. jpg
| image caption = Bradypus variegatus, a three toed sloth
| image2 = Choloepus hoffmanni (Puerto Viejo, CR) crop. jpg
| image2 caption = Choloepus hoffmanni, a two toed sloth
| display parents = 2
| taxon = Folivora
| authority = Delsuc, Catzeflis, Stanhope, and Douzery, 2001 The two groups of sloths are from different, distantly related families, and are thought to have evolved their morphology via parallel evolution from terrestrial ancestors. Besides the extant species, many species of ground sloths ranging up to the size of elephants (like Megatherium) inhabited both North and South America during the Pleistocene Epoch. However, they became extinct during the Quaternary extinction event around 12,000 years ago, along with most large, bodied animals in the New World. The extinction correlates in time with the arrival of humans, but climate change has also been suggested to have contributed. Members of an endemic radiation of Caribbean sloths also formerly lived in the Greater Antilles but became extinct after humans settled the archipelago in the mid Holocene, around 6,000 years ago. Sloths are so named because of their very low metabolism and deliberate movements. Sloth, related to slow, literally means "laziness," and their common names in several other languages (e. g. Faultier, , lang es, Romanian: leneș, Finnish: laiskiainen) also mean "lazy" or similar. Their slowness permits their low energy diet of leaves and avoids detection by predatory hawks and cats that hunt by sight.

Sloths can be long and, depending on the species, weigh from Two toed sloths are slightly larger than three toed sloths. Sloths have long limbs and rounded heads with tiny ears. Three toed sloths also have stubby tails about long. Sloths are unusual among mammals in not having seven cervical vertebrae. Two toed sloths have five to seven, while three toed sloths have eight or nine. The other mammals not having seven are the manatees, with six.

Sloths have colour vision but have poor visual acuity. They also have poor hearing. Thus, they rely on their sense of smell and touch to find food. Sloths have very low metabolic rates (less than half of that expected for a mammal of their size), and low body temperatures: when active, and still lower when resting. Sloths are heterothermic, meaning their body temperature may vary according to the environment, normally ranging from , but able to drop to as low as , inducing torpor. from predatory jaguars, ocelots, and harpy eagles. Because of the algae, sloth fur is a small ecosystem of its own, hosting many species of commensal and parasitic arthropods. There are a large number of arthropods associated with sloths. These include biting and blood sucking flies such as mosquitoes and sandflies, triatomine bugs, lice, ticks and mites. Sloths have a highly specific community of commensal beetles, mites and moths. The species of sloths recorded to host arthropods include

Their limbs are adapted for hanging and grasping, not for supporting their weight. Muscle mass makes up only 25 to 30 percent of their total body weight. Most other mammals have a muscle mass that makes up 40 to 45 percent of their total body weight. Their specialised hands and feet have long, curved claws to allow them to hang upside down from branches without effort, and are used to drag themselves along the ground, since they cannot walk. On three toed sloths, the arms are 50 percent longer than the legs. Sloths are surprisingly strong swimmers and can reach speeds of per minute. They use their long arms to paddle through the water and can cross rivers and swim between islands. Sloths can reduce their already slow metabolism even further and slow their heart rate to less than a third of normal, allowing them to hold their breath underwater for up to 40 minutes. Wild brown throated three toed sloths sleep on average 9.6 hours a day. Two toed sloths are nocturnal. Three toed sloths are mostly nocturnal but can be active in the day. They spend 90 per cent of their time motionless. though female sloths do sometimes congregate, more so than do males. Sloths descend about once every eight days to defecate on the ground. The reason and mechanism behind this behavior have long been debated among scientists. There are at least five hypotheses: 1) fertilize trees when feces are deposited at the base of the tree; 2) cover feces and avoid predation; 3) chemical communication between individuals; 4) pick up trace nutrients in their claws, that are then ingested; and 5) favor a mutualistic relationship with populations of fur moths.

Baby sloths learn what to eat by licking the lips of their mother. All sloths eat the leaves of Cecropia. Two toed sloths are omnivorous, with a diverse diet of insects, carrion, fruits, leaves and small lizards, ranging over up to Three toed sloths, on the other hand, are almost entirely herbivorous (plant eaters), with a limited diet of leaves from only a few trees, Recent research shows that moths, which live in the sloth's fur, lay eggs in the sloth's feces. When they hatch, the larvae feed on the feces, and when mature fly up onto the sloth above. These moths may have a symbiotic relationship with sloths, as they live in the fur and promote growth of algae, which the sloths eat.

The pale and brown throated three toed sloths mate seasonally, while the maned three toed sloth breeds at any time of the year. The reproduction of pygmy three toed sloths is currently unknown. Litters are of one newborn only, after six months' gestation for three toed, and 12 months for two toed. Newborns stay with their mother for about five months. In some cases, young sloths die from a fall indirectly because the mothers prove unwilling to leave the safety of the trees to retrieve the young. Females normally bear one baby every year, but sometimes sloths' low level of movement actually keeps females from finding males for longer than one year. Sloths are not particularly sexually dimorphic and several zoos have received sloths of the wrong sex. The average lifespan of two toed sloths in the wild is currently unknown due to a lack of full lifespan studies in a natural environment. Median life expectancy in human care is about 16 years, with one individual at the Smithsonian Institution's National Zoo reaching an age of 49 years before her death.

Although habitat is limited to the tropical rainforests of Central and South America, in that environment sloths are successful. On Barro Colorado Island in Panama, sloths have been estimated to constitute 70% of the biomass of arboreal mammals. Four of the six living species are currently rated "least concern"; the maned three toed sloth (Bradypus torquatus), which inhabits Brazil's dwindling Atlantic Forest, is classified as "vulnerable", while the island dwelling pygmy three toed sloth (B. pygmaeus) is critically endangered. Sloths' lower metabolism confines them to the tropics, and they adopt thermoregulation behaviors of cold blooded animals such as sunning themselves.

The majority of recorded sloth deaths in Costa Rica are due to contact with electrical lines and poachers. Their claws also provide another, unexpected deterrent to human hunters; when hanging upside down in a tree, they are held in place by the claws themselves and often do not fall down even if shot from below. Sloths are victims of animal trafficking where they are sold as pets. However, they make very poor pets, as they have such a specialized ecology. The Sloth Institute Costa Rica is known for caring, rehabilitating and releasing sloths back into the wild. Also in Costa Rica, the Aviarios Sloth Sanctuary cares for sloths. It has rehabilitated and returned about 130 individuals to the wild. However, a report in May 2016 featured two former veterinarians from the facility who were critical of the sanctuary's efforts, accusing it of mistreating the animals.