Sloths may be in danger by the end of the century

Central and South America’s sloth populations may face a dire existential threat from climate change by the end of the century. New research published on September 27 in the journal PeerJ indicates that simply from a metabolic standpoint, Earth’s rising temperatures could pose a severe threat to the overall species’ health and long-term survival rates.

Led by Rebecca Cliffe, a zoologist and founder of The Sloth Conservation Foundation, experts focused their most recent investigation on two-fingered sloths (Choloepus hoffmanni), which live in both high- and lowland areas that feature a spectrum of average ambient temperatures. By employing a methodology known as indirect calorimetry, Cliffe’s team analyzed the sloths’ oxygen consumption and core body temperatures in situations that mirrored the warming rates projected for their habitats by 2100—somewhere between 2-to-6 degrees Celsius (3.6-to-10.8 degrees Fahrenheit). According to their study, the consequences “are expected to be profound.”

[Related: Sloth schedules are surprisingly flexible.]

“Sloths are inherently limited by their slow metabolism and unique inability to regulate body temperature effectively, unlike most mammals,” Cliffe explained in an accompanying statement. “Our research shows that sloths, particularly in high-altitude regions, may not be able to survive the significant increases in temperature forecast for 2100.”

The biggest issues for higher altitude sloths stem from a sharp increase in resting metabolic rate (RMR) when faced with warmer temperatures. This is especially problematic given their limited metabolic adaptability and difficulty finding any cooler habitats. In contrast, while low-altitude sloths may potentially be able to move to higher altitudes to find cooler homes, they still displayed a biological survival trait called “metabolic depression” that limits any further increase in RMR. This alone would pose its own threats to their health.

It’s not just sloth metabolisms that are worrisome, either. The animal’s digestion rate can be as much as 24-times slower than similarly sized herbivores. This means that they can’t simply eat more food as both global temperatures and sloth metabolic rates rise.

Cliffe’s team concedes in the study that their climate model was “rudimentary in its omission of error and uncertainty considerations.” Despite this, they “predict that a comparatively small increase in ambient temperature could see high-altitude sloths pushed into a situation where it is impossible to make their energy consumption tie in with their energy budget.” It’s this delicate balance between metabolism, digestion, and habitat temperatures that make the slow-moving species especially susceptible to climate change fallout.