Sloths, renowned for their slow pace and native to Central and South America, may face significant threats from climate change, according to a study led by Rebecca Cliffe of The Sloth Conservation Foundation, published in PeerJ Life & Environment. The research examined how sloths respond metabolically to rising temperatures, suggesting that their energy limitations could jeopardize their survival by the end of the century, particularly for populations living at higher altitudes. The study focused on the two-toed sloth (Choloepus hoffmanni), which inhabits both highland and lowland areas, analyzing how they react to varying environmental temperatures.
Using indirect calorimetry, the researchers measured sloths’ oxygen consumption and body temperature under conditions mimicking anticipated climate shifts. The findings paint a troubling picture, especially for sloths living in elevated regions. “Sloths are naturally constrained by their slow metabolism and their poor ability to regulate body temperature, unlike most mammals,” said Cliffe. “Our research suggests that sloths, particularly those in high-altitude regions, may struggle to survive the significant temperature increases projected for 2100.”
High-altitude sloths experience a sharp rise in resting metabolic rate (RMR) as temperatures increase. In contrast, lowland sloths, while better adapted to warmer environments, enter a state of metabolic depression when temperatures exceed their comfort zone, known as the “thermally active zone” (TAZ). By 2100, with temperature increases predicted between 2°C and 6°C in sloth habitats, high-altitude sloths are expected to face a substantial metabolic burden.
Their limited ability to process energy, along with minimal capacity to migrate to more suitable environments, could prevent them from adapting to a warming climate. Additionally, sloths’ extremely slow digestion—up to 24 times slower than that of other herbivores of similar size—poses a further challenge: any increase in metabolic demand due to climate change cannot be easily met by a higher food intake, making it difficult for sloths to maintain their energy balance.
