Are sloths' days numbered?

Sloths - two-toed, three-toed, pygmy, any and all sloths - have always been among my favourite animals. Ever since I helped one across a busy road in Venezuela many years ago, and realized just how lightweight and vulnerable they really are, I have been smitten. I'm also impressed - and, frankly, shocked - at how something so apparently defenceless and exposed has managed to survive, virtually unchanged, for 64 million years. They move so slowly that algae and moss grow on them!

Now, of course, I know they are not actually defenceless. Those rapier-like claws can slash out faster than you might think, and are a prodigious defensive armament. And, if they only come down out of the trees to pee and poo once a week, their exposure to terrestrial predators is severely limited. (Incidentally, has anyone questioned why they come down at all? Can't they pee and poo from up above?) They are also masters of disguise and supremely camouflaged in their arboreal domain, as anyone who has tried looking for them can attest.

Now, though, it seems like sloths may finally be existentially threatened by - what else? - anthropogenic climate change. Sloth population studies are finding reduced numbers in recent years, and it seems the main culprit may be the prolonged periods of extreme heat interspersed with unaccustomed periods of extreme cold being experienced in the sloths' native habitat in Central America and northern South America. 

The microbes in the sloths' stomachs that help digest their diet of tree leaves - and remember, it can take a sloth's ultra-slow metabolism a whole month to digest a single leaf! - may be dying off during the cold spells. So, although the sloths may be eating and looking well, they are not actually digesting their food properly, and consequently are getting weaker and weaker, and ultimately dying.

This research is still in its infancy. But things are not looking so rosy for the poor sloth.