Amid Rising Temperatures, Sloths’ Slowness May Put Their Survival at Risk

In the tropical rainforests of Central and South America, sloths move through the branches at a sluggish pace. With a low metabolic rate, they lounge and sleep between the treetops for 15 to 20 hours a day. Now, new research shows that rising temperatures are putting the survival of these slow-moving tree dwellers at risk.

In a study published on Friday in PeerJ Life & Environment, researchers found that two-fingered sloths (Choloepus hoffmanni) will face profound consequences by the end of the century. The sloth’s low metabolic rate and limited dispersion will make it unsuitable to survive rising temperatures, especially in high-altitude areas.

"Sloths are uniquely vulnerable to rising temperatures due to their physiological adaptations," Rebecca Cliffe, founder and executive director of the Sloth Conservation Foundation and lead author of the study, tells Newsweek’s Tom Howarth. "They survive on an extremely low-calorie diet, so conserving energy is critical for them.”

The researchers studied 12 adult two-fingered sloths at the Sloth Sanctuary of Costa Rica and analyzed their core body temperatures and oxygen consumption. These sloths, hailing from both highland and lowland rainforests, responded differently to ambient temperatures between 18 and 34 degrees Celsius (64 and 93 degrees Fahrenheit).

Sloths from lowland areas showed a better adaptation to warmer conditions, decreasing their metabolic activity when temperatures exceeded 32 degrees Celsius (nearly 90 degrees Fahrenheit). In contrast, highland sloths did not possess this adaptation, leading to a significant rise in their resting metabolic rate and a need for more food.

Sloths digest food very slowly—up to 24 times slower than similar-sized herbivores. And unfortunately, they cannot offset this metabolic increase by consuming more food due to their slow digestive process.

"High-altitude sloths are in a particularly precarious position," Cliffe tells the Independent’s Stuti Mishra. "Their limited ability to migrate to cooler areas and the lack of metabolic flexibility could push these populations toward extinction."

By 2100, sloth habitats could see a temperature increase of 2 to 6 degrees Celsius. Lowland sloths may manage to survive by moving to other areas, but those already residing in mountainous areas have no geographical room to escape rising temperatures. For these high-altitude sloths, a significant metabolic strain means they may not be able to survive.

"Unlike some species, sloths are creatures of habit, highly specialized in their habitat, and are not suitable for translocation to other regions,” Cliffe says to Newsweek. “If their environment becomes too hot, their survival is unlikely."

The researchers acknowledge that their climate model was basic and perhaps didn’t fully account for errors and uncertainties. Still, they predict that even a slight rise in temperature could force high-altitude sloths into a situation where they need to balance their energy input and output. And, as they say in the study, “this option appears biologically implausible for sloths due to their slow digestive rate and constantly full stomach." 

"Our work highlights the vulnerability of sloths to a warming world," Cliffe tells the Independent. "If we don’t take urgent action to protect these species, we risk losing them forever."

Alexa Robles-Gil | | READ MORE

Alexa Robles-Gil is a bilingual science journalist based in New York City. Her work has appeared in the Guardian, Undark, Inside Climate News and more.