Page last updated at 23:07 GMT, Tuesday, 13 May 2008 00:07 UK

Sloth's lazy image 'a myth'

By Helen Briggs
Science reporter, BBC News

Sleeping sloth (Image: Bryson Voirin)
The three-toed sloth is the slowest mammal in the world

The sloth's popular image as a lazy creature that sleeps for most of the day has been called into question.

Rather than snoozing for more than 16 hours a day, as observed in captivity, sloths in the wild doze for less than 10 hours, research suggests.

Scientists caught sloths living in the rainforest of Panama and fitted them with a device that monitors sleep.

The findings, published in a Royal Society journal, may help shed light on human sleep disorders, they say.

Lead researcher Niels Rattenborg, of the Max Planck Institute for Ornithology in Starnberg, Germany, said the study demonstrated for the first time that it was possible to record sleep in a wild animal.

They don't seem to sleep an inordinate amount of time
Dr Niels Rattenborg

"The real exciting finding was that they only slept 9.6 hours a day, which is much less than what people popularly believed and less than had been observed in a previous study of sloths in captivity," he told BBC News.

"So they still may be sloth-like in terms of their speed of movement but in terms of their sleep they don't seem to sleep an inordinate amount of time."

The work, published in the Royal Society journal Biology Letters, attempts to find traits that predict whether an animal sleeps more or less than another species. This might provide clues to the function of sleep, said Dr Rattenborg.


Proof of principle

Animals vary in the amount of sleep they need. Pythons, for example, sleep for 18 hours a day, while giraffes survive on just two hours.

Sleeping sloth (Image: Bryson Voirin)
They spend much of their time in trees



The animals were fitted with the data recorder and then released.

When re-captured several days later, measurements showed that they slept for an average of 9.6 hours a day, compared with a sleep time of 16 hours a day reported in sloths kept in captivity.


"It's intuitive that animals would sleep less in the wild than in captivity - this technology gives us the opportunity to prove that's true," he said.



Scientists compile 'book of life'
09 May 07 |  Science/Nature


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