There is a reason why sloths are only found in neotropical rainforests – because the weather is warm, humid and relatively stable all year round. Sloths are unable to regulate their own body temperatures like most mammals, and instead are completely reliant on the environmental conditions. This means that when it is too hot or too cold, sloths have to modify their behaviour accordingly. On hot days, sloths move very little (because movement generates even more body heat). They drop down to the lower canopy, find some shade, spread out their limbs and wait for the temperature to cool down. When it is too cold, sloths either have to warm their body temperature by basking, or they have to just sit still, curl in a ball and wait for the sun to come out.
Although the tropics do sometimes experience temperature extremes (cold depressions and heat waves), temperatures typically stay within a very narrow range. For example, during my sloth studies I set up a remote weather station and monitored the conditions for 3 continuous years. The temperature on the Caribbean coast of Costa Rica never dropped below 23℃, even in the middle of the night. However, this is no longer the case. During the end of 2017 and the beginning of 2018, the temperature in the Caribbean has plummeted. In December we experienced our first tropical storm on record, and temperatures frequently fluctuated below 20℃ for weeks on end. Species that live in the tropics have evolved over millions of years in a climatically very stable environment, and as such, they do not have the flexibility to cope with extreme, rapid weather changes. This is particularly the case for sloths.
Sadly, as a result of the cold temperatures, we are seeing a huge increase in the number of sloths that are being brought into rescue centres because they are starving to death. This is not because they can’t find enough food (there are still plenty of leaves on the trees), but rather because they can’t digest the food that they are eating. Sloths rely on a range of symbiotic gut bacteria and microbes in their stomach to break down the tough cellulose in the leaves that they eat, and these microbes are temperature dependant. When the environmental temperature drops, so does the sloths body temperature, and if it drops too low then the bacteria and microbes die. In this situation, the sloth can eat the same amount of leaves as normal but can starve to death on a full stomach because they can’t extract any nutrients. The only way to save these animals is to replenish the gut bacteria. This can be done by feeding with probiotics and (in extreme cases) faecal matter from a healthy sloth – something that rescue centres fondly refer to as a ‘poop cocktail’. But the real problem that we need to address is the changing climate. While some people may shake their heads, there is no way to deny that the weather patterns in the tropics are becoming progressively more unstable. Unfortunately, there is also no easy fix. It is going to require a collective effort by the human population to reverse the already apparent effects of climate warming. All we can really do is each do our best on an individual level to reduce our carbon footprint. Eat less meat, utilise public transport, walk or ride your bike instead of driving, recycle and try to cut down on your use of products that negatively impact the environment (this includes plastics as well as products that stem from the monoculture plantations that are responsible for a huge proportion of deforestation – palm oil, mass produced fruit etc.).
It may seem overwhelming, but as the famous anthropologist Margaret Mead once said: “Never doubt that a small group of concerned citizens can change the world. Indeed, it’s the only thing that ever has”.