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Thursday, 8 July 2010

Sloths are Green (Less Haste, More Sloth)

I want to share with you how "scintillating" sloths can be.  Sloths have had an undeserved image of laziness, "Sloth" being one of The Seven Deadly Sins.  In 1772, the French naturalist Georges Buffon, said "These sloth are the lowest form of existence".   In fact their slow movement has many benefits, their graceful movement being compared to a Tai Chi master.  They are the slowest mammals on Earth, and masters at conserving energy ! Truth is, they are one of the better adapted animals on our planet. 


 Sloths are members of a group of mammals that have been around for 60 million years.  There was once a group of giant, marine, amphibious sloths!  The following link may explain why they are such good swimmers: Giant swimming sloth 

There are now, 6 species divided into two families: two-toed sloth and three-toed sloth, named after the number of toes on their front feet.  The Three-toed sloth is smaller and has extra neck bones allowing it to turn it's head almost 360 degrees, further than any other mammal.  Sloths are arboreal, living in trees in the rainforests of Central and South America.  The Maned Three-toed Sloth, is endangered and the ongoing destruction of the rainforests may soon threaten the other species.

                                                                      Praziquantel image

Sloths move at 15-30 cm per minute to conserve energy. When in danger they can move up to 5 metres per minute through the trees, or crawl 1.5 metres per minute on the ground.  One reason for their slow movement is their low metabolism.  A diet of leaves is low in nutrients.  Leaves are digested slowly, taking as long as a month in their specialised stomachs. Their stomachs have multiple compartments housing symbiotic bacteria to break down the tough leaves and account for two thirds of the sloth's weight.  Sloths will lick their fur and absorb bacteria through their skin for extra nutrients.
They get by with half as much muscle mass as a mammal the same size, as maintaining muscle would require large amounts of food energy. This means that they weigh half as much and can climb high to the thin branches in the forest canopy, where it is easier to find food and avoid heavier predators.

A high body temperature takes energy.  Sloths reduce this cost by maintaining a lower than average body temperature than other mammals.  Like reptiles, they sunbathe in the morning, then retreat to the shade during the hottest part of the day.  It used to be thought that they slept up to 20 hours per day to conserve energy but now it is known to be half that time.  BBC News: Sloth's lazy image a myth

Sloth fur contains an entire ecosystem of it's own ! It's fur hosts algae and provides shelter and a good supply of water to many non-parasitic insects.  One study found over 950 beetles on a single sloth.  There is a species of moth that exists only on sloth.  When the sloth descends to the ground to defecate the moth quickly lays it's eggs in the dung and returns to the sloth fur.  120 of these moths have been found on one animal.

The fur has hairs that grow in the opposite direction to other mammals.  Adapted to a life hanging upside down in trees, the hair grows from the stomach to the back and away from the extremeties to facillitate water run-off, and provide protection from the elements.  The algae turn the sloth green in the rainy season and provide camouflage.  As long as the sloth remains quiet and still, it is near invisible and blends with the trees, avoiding jaguars, harpy eagle and humans.  They do blow their cover when they emit a shrill call to attract a mate.

                                                                      henryalien image

Almost all thier lives are spent hanging upside down in trees.  Eating, sleeping and giving birth, hanging from their curved claws.  Even after death they can still be found hanging from the trees, this deters hunters from killing them as they don't fall to the ground.  Scientists are still baffled by why sloths will only urinate and defecate hanging from a tree in the rainy season but make a weekly descent to the ground to defacate when it's dry.  It is thought that despite the danger, it provides fertiliser for the tree the sloth lives on. The long wait means up to 2lbs of stored dung is produced from a 10lb animal !

                                                                               brian.gratwicke image

 A strange mixture of plant and animal and masters of the upside down.  Sloths have the antidote for our fast lives.  Maybe that explains their persistent smiles.

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