Three-toed sloths (Bradypus variegatus) are arguably one of nature’s most interesting animals. The sloth’s seemingly sedentary and boring lifestyle masks their fascinating environmental adaptations and evolutionary history. Researchers have recently discovered how these amazing creatures deal with extreme flooding in their habitats, once again demonstrating their unique anatomical adaptations.
Sloths are folivorous, meaning that they exclusively eat leaves. This is thanks to their compartmentalized stomach which allows for the breakdown of tough plant cell walls via fermentation. In the Amazonian igapó ecosystem, trees are evergreen which allows for the sloths to forage for their food year round. However, their environment experiences intense annual flooding periods. During the flooding season, the rivers flood up to 10m for a period of 9 months causing 80% of tree species to shed their leaves due to the stress. Due to the scarcity of young leaves during this season, sloths may need to increase their home range to forage. An animal’s home range is where an individual frequents to find food, mates, shelter etc. Home ranges can be affected by living and nonliving factors in the environment, like flooding. An animal may increase its home range when resources are scarce, causing them to search farther and farther away for food. Castro-Sa et al. 2021 aimed to investigate whether igapó sloths increase their home range during the flood season to find more easily digestible young leaves.
Over a period of 6 months, 5 individual sloths were tracked using radio collars and a handheld GPS. This allowed researchers to follow the 5 sloths’ near exact locations for 6 months. Two female sloths and three male sloths were fitted with a radio collar, and the sloth was returned to the tree it was found in. During a 6 month period, researchers visited the locations of the sloths for 10 days a month to use a handheld GPS and mark the trees the sloths fed in with a flag. To measure the flooding levels and the availability of leaves, researchers installed transects. These divided the forest into 3 levels of flood intensity based on duration; level one was a long flooding duration of greater than 200 days, level two had a medium duration of flooding of 100-200 days, and level three had a short duration of flooding less than 100 days. Within these areas, 570 individual trees were monitored monthly for young and mature leaves. The crown of each tree was divided into four sections and given an intensity score from 0 to 4 of young to mature leaves. Due to the extreme flooding, researchers had to omit data in July and August since they were unable to monitor leaf growth, and data in December because not enough GPS locations were collected.
Castro-Sa et al. 2021 found that these three-toed sloths did not change their home ranges based on young leaf availability or river level. This is unlike many other mammals who might have to use alternative food sources or migrate to new areas to find food when resources are scarce. The researchers concluded that sloths were able to maintain their stable diets even in extreme conditions because their highly adapted stomachs allow them to get adequate nutrition from mature leaves when young leaves were less available. In addition, sloths also rely on a species of rubber tree (Hevea spruceana) that grows new leaves quickly when most of the other tree species are shedding. These findings are important because understanding the dispersal and movement of three-toed sloths could help researchers protect the critically endangered species.
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