Misunderstood Sloths and Slothery

My favourite animal has long been the 2 toed sloth, with a top speed when chased by a predator of 0.5mph. You don’t get more laid back than that, but if they are so inefficient, how have they managed to survive? This article from the i a few weeks back, by Becky Cliffe provides some answers

Conventional wisdom has it that sloths are simple, lazy creatures that do very little other than sleep all day. Eve the very name “sloth” in most languages translates as some version of lazy. It seems astonishing that such an animal survives in the wild at all. In 1749 the French naturalist Georges Buffon was the fist to describe the creature in his encyclopedia of life science, saying: “Slowness, habitual pain, and stupidity are the results of this strange and bungled conformation. These sloths are the lowest form of existence. One more defect would have made their lives impossible.”

Yet the fact that slow sloths have been on this planet for almost 64 million years shows that slowness is their winning strategy. three-toed sloths are indeed the slowest moving mammals on earth. At the world’s only sloth sanctuary in Costa Rica, we have been monitoring the movement and activity patterns of wild sloths using small data loggers combined with tracking devices inside specially built “sloth backpacks”. We have found that, contrary to popular believe, sloths do not actually spend inordinate amounts of time sleeping; they sleep for just 8 to 10 hours a day in the wild. they do move, but very slowly and always at the same, almost measured, pace. Moving slowly requires less energy than moving fast, and it is this principle that underlies the sloths’ unusual ecology. They operate at lower body temperatures than most mammals., while apparently having a reduced ability to thermoregulate. The average temperature fo a 3 toed sloth is around 32.7ded C (91F) compared to humans 36.5C (97.8F).

Sloths depend on behavioural and postural adjustments to control their own heat loss and gain, showing daily core temperatures fluctuations of up to 10 deg C. By perpetually moving slowly and partially departing from full homeothermy, sloths burn very little energy and are able to function with the lowest metabolic rate of any non-hibernating mammal.

As a result of all this, sloths don’t need to acquire much energy or to spend time looking for it. Both 2 and 3 fingered sloths have a predominantly leaf-based diet, consuming material with a notably low caloric content. Fellow leaf-eating howler monkeys move at a normal pace but consume 3 times as many leaves per kg of body mass as sloths, digesting their foodstuff comparatively quickly.

It is an extraordinary lifestyle, with sloths living on a metabolic knife edge, where minimal energy expenditure is finely balanced with minimal energy intake. With their plethora of energy-saving adaptations, sloths physically don’t have the ability to move very fast. And with this, they do not  have the capacity to defend themselves or run away from predators, as a monkey might. Instead, their survival is entirely dependent upon camouflage – a factor aided by their symbiotic relationship with algae growing on their fur. Sloths’ main predators – big cats such as jaguars and ocelots and birds such as harpy eagles – all primarily detect their prey visually, and it is likely that sloths simply move at a pace that doesn’t get them noticed. 

The sloth life is certainly not the “lowest form of existence” but as strategic as that of any other animal.

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