Hoffman's two-toed sloth. Photo courtesy of Wrylie Guffey, Topeka Zoo.
Hoffman’s two-toed sloth. Photo courtesy of Wrylie Guffey, Topeka Zoo.

Living sloths (which comprise the taxonomic suborder Folivora) inhabit the rainforest canopy of Central and South America. Unlike other xenarthrans they are entirely herbivorous, subsisting primarily on leaves. Flowers and limited amounts of fruit might also be taken depending upon the species.

There are two families of sloths and these are most readily distinguished from one another by number of claws they possess: the three-toed sloth (Bradypodidae) has three claws on all four limbs; the two-toed sloth (Megalonychidae) has two claws on the forelimb and three on the hindlimb.

Male pygmy sloth, Bradypus pygmaeus, in mangroves. Photo courtesy of Melanie Sorensen
Male pygmy sloth, Bradypus pygmaeus, in mangroves. Photo courtesy of Melanie Sorensen

Three-toed sloths are more obligate folivores than two-toed sloths. Bradypus variegatus and Bradypus trivirgatus have occasionally been housed in North American zoological collections. While some of their congeners are species of conservation concern, these two species are widely distributed in relatively undisturbed habitats in nature. Three-toed sloths have never been widely held in human care, nor have they reliable reproduced. Consequently, the PAX TAG has not designated any programs for these species. There are yellow SSP programs for the two Two-toed sloth species.

Throughout their history in zoos, there has been some difficulty in differentiating between Hoffman’s two-toed sloths (Choloepus hoffmanni) and Linne’s two-toed sloths (Choloepus didactylus). Application of subjective determinants in distinguishing these two species from each other has resulted in some animals being incorrectly identified. This resulted in hybrids, animals that have had their species changed in the studbook, and animals that still have not been classified because of incomplete data. Recently, a DNA test was established that is able to correctly identify the species. This test can only track a species according to the maternal lineage, so it is unable to verify hybrids. Nonetheless, it is an important step in correctly classifying the North American population of two-toed sloths.

Photo courtesy of Wrylie Guffey, Topeka Zoo
Choloepus hoffmanni with infant. Photo courtesy of Wrylie Guffey, Topeka Zoo.

Furthermore, it is also difficult to distinguish the genders of two-toed sloths. Therefore, over time, some individuals have had their sex classification changed within the studbook.

The PAX TAG is in the process of sorting out the two-toed sloth populations. We have made great progress in being able to correctly identify individuals since the publication of the last studbook. We will continue to ask for participation from AZA institutions to submit samples from their sloths for DNA analysis as well as seek assistance if an individual sloth has been identified as the wrong gender.

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