According to Wetzel (3), Bradypus torquatus is possibly the South American mammalian species closest to extinction. Bradypus torquatus (the maned sloth) is regarded as an endangered species, its numbers having fallen catastrophically with the destruction of the Atlantic coast forest (Mata Atlântica) in southeastern Brazil. The distribution of the present day sloths was illustrated in the earlier review (1). In 1992 its presence was recorded in the Yungas region of Bolivia, considerably further south than previously reported (5). It is less well-adapted to the drier areas than is Bradypus. Choloepus didactylus is found from the delta of the Orinoco River west to the upper drainage of this river in Colombia, east through French Guiana and in Brazil to the State of Maranhão. This may make the sloth appear pop-eyed during periods of stress or prior to the onset of aggressive behavior when the lids appear to rise from their orbits. It has been reported (4) that the eyes can be partially retracted when the lids are tightly closed. The ears are rounded and thickened and almost always covered with hair. The hair of this species is lighter than in Choloepus didactylus. The species is still common, but its numbers are fewer in areas where it coexists with the three-toed sloth. Of the two living species of Megalonychidae, Choloepus hoffmanni is found from the lowland forest to the higher altitudes of mountain forests south of Nicaragua through Central America and in Colombia, Venezuela, French Guiana, Ecuador, Peru, Brazil and Bolivia. Topics covered include the general ecology, behavior, nutrition and digestion as well as the large range of arthropods associated with sloths and the number of viruses they transmit. This paper is intended to update research undertaken since that time on other aspects of sloth biology. We have recently reviewed the literature in terms of the physiological studies carried out on two- and three-toed sloths (1) since Goffart (2) published Function and Form in the Sloth 30 years ago. Key words: sloths, ecology, behavior, parasites, Bradypus, Choloepus Sloths are known reservoirs of the flagellate protozoan which causes leishmaniasis in humans, and may also carry trypanosomes and the protozoan Pneumocystis carinii.
Sloths are hosts to a fascinating array of commensal and parasitic arthropods and are carriers of various arthropod-borne viruses. Nutrients derived from the food, particularly in Bradypus, only barely match the requirements for energy expenditure.
Activity shows circadian and seasonal variation. Sloth hair is extremely specialized for a wet tropical environment and contains symbiotic algae. The animals exhibit numerous fascinating features. This is a review of the research undertaken since 1971 on the behavior and physiological ecology of sloths.
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