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Levin: Behold the Sloth

05/26/10 12:50PM By Ted Levin
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(HOST) Earlier this spring, commentator Ted Levin had the opportunity to observe a sloth in the wild - for most of a day, in fact - since it behaved - well - just like a sloth.

(LEVIN) The brown-throated three-toed sloth, which hangs from hook-like claws upside down from rainforest branches, is the most lethargic, the most apparently dimwitted mammal I have ever watched. The sloth's vapid smile and vacant black eyes, windows apparently looking into nothingness, didn't do much to change my opinion.
    
A sloth is a study of slow motion; the slowest possible motion that would indicate the beast is still alive. I observed one recently in Costa Rica, bunched together in the fork of tree, thirty feet above the ground.
    
An intrepid nine year old naturalist, who took me there after breakfast, discovered the sloth.
    
It was early morning, cool. Fog rose out of the valley; everything dripped, including the sloth, whose green, algae-tinged fur appeared sparse, matted, and soaked.
    
I kept my eye on it for the remainder of the day - not a continuous vigil (I would have succumbed to boredom), but periodic visits. And by mid morning the sloth awoke and stretched its Captain Hook extremities. By noon it had moved to another branch, a journey of five feet. By mid-afternoon I hit the sloth jackpot. It was a she. A squirrel-sized baby clung to her belly fur.
    
Every time the mother grazed leaves the baby licked masticated greenery off her lips, which is how the mother conveys dietary information to her offspring. After six months, the mother abandons her pup and moves to another territory, deeding her territory to the pup: the epitome of mammalian nepotism.
    
So, there is more to the sloth than meets the eye.
    
Plenty more, actually.
    
Because sloths eat only hard-to-digest leaves, they have a very large hindgut (like a cow) at the expense of muscle mass. In fact, gut capacity is 30 percent of the total body weight. Hooked claws compensate for the lack of supportive muscle.
    
Rather than rain its waste down from the trees, a sloth eliminates only once a week. It climbs to the ground, digs a hole at the base of the tree with its stubby tail, voids, covers it up, and returns to the treetops.
    
This odd behavior serves multiple purposes. Predators like jaguars cannot locate the sloth by smelling its waste; waste matter is a nutrient boost to the host tree, whose leaves support the sloth; and the load of moths, beetles, and mites, which live in the sloth fur and dine on algae, deposit their eggs in the feces, which the larvae eat. After the eggs are laid, the sloth's passengers have plenty of time to climb back aboard. These invertebrates, by the way, live nowhere else in the world but on a sloth - it's the very essence of co-evolution.
    
Sloths are abundant, primitive, and among the most important primary consumers in the Neotropics. And when they climb into the canopy to bask in the sun, they're often cherry-picked by the harpy eagle, one of the planet's most awesome birds of prey.
    
That blank look belies a vital ecological role.
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