By Matt Walker
Editor, Earth News
Emerging from a human toilet
Two-toed sloths have been recorded descending from the trees to feed out of a human toilet.
The extraordinary behaviour, recorded on at least 25 occasions in the Amazon rainforest of Peru, has stumped the biologists who witnessed it.
The sloths either crawl into the latrine to feed from it or scoop out the excrement and waste within.
The feeding habit is even more bizarre as wild sloths are plant eaters not known to feed on animal matter.
Details of the behaviour are published in the journal Mammalian Biology.
Researchers speculate the sloths must derive some nutritional benefit from their bizarre feeding habit, though it is unclear exactly what that might be.
The behaviour was recorded over a number of years by biologists working at the Estacion Biologica Quebrada Blanco field research site located in the Amazon rainforest in northeastern Peru.
The biologists based there usually study the behaviour and ecology of New World monkeys, including moustached tamarins, saddle-back tamarins and red titi monkeys.
Their camp is a traditionally built hut, with latrines located 20 to 40m away in the forest.
On the first occasion, a researcher using the latrine saw a two-toed sloth (Choloepus didactylus) hanging upside down from the wooden bars that enclose the toilet.
A grounded sloth is a rare sight
It was using one hand to scoop out handfuls of semi-liquid manure, comprising human faeces, urine and toilet paper, and then eating from the hand.
Since that occasion, the scientists have since recorded sloths visiting the latrine on at least 25 other occasions.
Sometimes the sloths entered the pit that formed the latrine, to feed directly from the waste inside, emerging covered in the liquid held within.
Professor Eckhard Heymann of the German Primate Centre based in Gottingen, Germany, who led the team of researchers, told the BBC that they were surprised and astonished by the behaviour.
"The sequence of events was always more or less then same: someone arriving at the latrine, seeing the sloth inside and the sloth feeling disturbed and coming out and moving away," says Prof Heymann.
The researchers suspect many individual sloths visited the latrines: on one occasion a mother and baby visited.
Why the sloths decided to visit and feed from the latrines remains a mystery.
Sloths hardly ever come down from the trees in which they live.
Usually they only descend to the forest floor to change trees or once every three to seven days to defecate.
One idea put forward by Prof Heymann's team is that the human faeces may provide a direct source of nutrients, as faeces can contain variable amounts of fibre and energy in the form of proteins, sugars and fatty acids.
Another is that the sloths visit to acquire sodium or other minerals in the waste, in the same way that some animals visit salt licks.
Heading for the trees after visiting the toilet
The third proposal is that the sloths may be eating insect larvae that grow among the waste.
While wild sloths are plant eaters, captive sloths have been known to accept meat and fish in their food, suggesting the animals may seek out larvae as an additional source of protein.
The odd behaviour may also come at a cost to the sloths, however.
"While at first glance our observations may simply represent a bizarre contribution to the natural history of sloths, they also bear implications for the transmission of disease from humans to wildlife," the researchers write in the journal.
Two-toed sloths can survive in secondary or disturbed forest close to human settlements.
If other sloths have developed similar tastes for human waste, it could increase the possibility of them acquiring human diseases and parasites.