Sloths are slow-moving, arboreal mammals native to the tropical rainforests of Central and South America. They spend almost their entire lives hanging upside down in the canopy, supported by specialized anatomy and an extremely low metabolism. Six species of sloths are currently recognized, divided into two distinct families based on the number of digits on their forelimbs. This article examines the conservation challenges each of the six species faces across its natural range.
Identifying the Six Sloth Species
The six living sloth species are categorized into two families: the three-toed sloths (Bradypodidae) and the two-toed sloths (Megalonychidae). The three-toed sloths, belonging to the genus Bradypus, are smaller and have a specialized diet, primarily consuming leaves from only a few select tree species. This family includes four species: the Pygmy Three-toed Sloth, the Maned Three-toed Sloth, the Pale-throated Three-toed Sloth, and the Brown-throated Three-toed Sloth.
The two-toed sloths, belonging to the genus Choloepus, are physically larger than their three-toed relatives and have a more generalized diet. Their diet includes fruits, shoots, and small animal matter in addition to leaves. This family is represented by the Linnaeus’s Two-toed Sloth and the Hoffmann’s Two-toed Sloth. The anatomical distinction is that while all six species have three clawed digits on their hind limbs, two-toed sloths only have two claws on their forelimbs.
Conservation Status of Three-Toed Sloths
The conservation status of the four three-toed species varies significantly, reflecting the importance of geography and habitat specialization. The International Union for Conservation of Nature (IUCN) Red List assigns a risk category based on factors like population decline and geographic range size. Two of the four three-toed species are currently listed in a threatened category.
The Pygmy Three-toed Sloth (Bradypus pygmaeus) is classified as Critically Endangered (CR), meaning it faces an extremely high risk of extinction in the wild. This species is endemic to Isla Escudo de Veraguas, a single small island off the coast of Panama measuring only about 4.3 square kilometers. Its severely limited range makes the population highly vulnerable to disturbance, with estimates suggesting fewer than 100 individuals remain.
The Maned Three-toed Sloth (Bradypus torquatus) is listed as Vulnerable (VU), indicating a high risk of extinction in the medium-term future. This species is restricted to the highly fragmented Atlantic Forest of eastern Brazil, a biome significantly reduced in size. Its population trend is decreasing due to the extensive loss of its native habitat.
In contrast, the Pale-throated Three-toed Sloth (Bradypus tridactylus) and the Brown-throated Three-toed Sloth (Bradypus variegatus) are both currently classified as Least Concern (LC). The Pale-throated species is found across the Guiana Shield region of northern South America. The Brown-throated species is the most widespread, ranging from Honduras down to northern Argentina.
This Least Concern status reflects their broad distribution and presumed large overall populations, which provides a buffer against localized extinction events. However, population densities for both species are declining in many parts of their range due to human activities. A global Least Concern status does not eliminate the need for conservation efforts at a regional level.
Conservation Status of Two-Toed Sloths
Both species of two-toed sloths are currently classified as Least Concern (LC) on the IUCN Red List. This status reflects their broader distribution and greater adaptability to various habitats compared to the specialized three-toed species. The Linnaeus’s Two-toed Sloth (Choloepus didactylus) is found across northern South America, including the Amazon basin in countries like Brazil, Colombia, and Peru.
The Hoffmann’s Two-toed Sloth (Choloepus hoffmanni) also holds a global Least Concern classification, ranging from Nicaragua to Peru and into parts of Brazil. This global assessment, however, masks significant regional concerns. Some local subpopulations are classified as Near Threatened or Endangered due to severe localized habitat loss.
The Linnaeus’s Two-toed Sloth has a single, continuous population, while the Hoffmann’s Two-toed Sloth has two distinct populations separated by the Andes Mountains. Both two-toed species are increasingly impacted by human encroachment. Their slower reproductive rates—typically a single offspring after a long gestation period—make their populations slow to recover from losses.
Causes of Population Decline
The primary driver of population decline for all six sloth species is the widespread destruction and fragmentation of their tropical forest habitat. Deforestation for agriculture, logging, and infrastructure development removes the canopy sloths rely on for movement, food, and shelter. When continuous tree cover is broken, sloths are forced to descend to the ground, where they become significantly more vulnerable.
Once on the ground, sloths face dangers they are not physiologically equipped to handle, such as vehicle collisions and attacks by domestic dogs. The fragmented landscape also causes sloths to use human infrastructure for travel, often resulting in fatal electrocutions on power lines. In some areas, over half of the wild animals admitted to rescue centers for electrocution injuries are sloths.
The illegal wildlife trade also poses a threat to sloth populations, particularly for the exotic pet market and the tourist trade. Sloths are frequently removed from the wild for photo opportunities or sale, which causes immense stress and often leads to high mortality rates. This practice is especially concerning for the two-toed species, which are often targeted.
Threats to Restricted-Range Species
For species with highly restricted ranges, such as the Pygmy Sloth, habitat degradation from localized tourism and logging of mangrove forests accelerates the risk of extinction. The isolation of these small populations also increases the potential for genetic bottlenecks. This makes them less resilient to disease or environmental changes.