Weekly Reader | Lead Story | Sloths Aren’t Sleepyheads

Place your cursor over the slideshow for captions.

loths may be the world’s slowest-moving mammals, but don’t call them lazy! That is what a team of scientists recently said after studying sloths’ sleep habits. They found that sloths sleep six hours a day less than previously believed. Instead of snoozing for 16 hours a day, the animals sleep less than
10 hours a day.

The scientists were the first to study animal sleep in the wild. All previous research had been done with animals in captivity. “It was a bit surprising. Sloths in the wild sleep a lot less than sloths in captivity,” says Roland Kays, a scientist who worked on the study and the curator of mammals at the New York State Museum in Albany. “We thought the sloths would sleep a little bit less in the wild, but six hours was much more than just an extra siesta.”

New Technology, Better Results

A sloth’s natural habitat is the rain forest. Sloths spend most of their time hanging upside down from trees. The scientists went to the rain forest of Panama to conduct their study. There they caught several three-toed sloths and glued a small sensor to each animal’s head. The sensors recorded the animals’ sleep patterns. The sloths were also fitted with radio collars so scientists could track their movements.

Because they are studying animals in the wild rather than in captivity, the scientists believe their results are more accurate. Until recently, studies were not conducted in the wild because the recording equipment was too big and heavy to place on a moving animal. Now, the equipment is much smaller.

Critical Thinking

Why might some animals need more sleep than others?

The scientists are excited about the results of the study. They hope it will help them better understand the purpose of sleep in all animals, including people. “What is the purpose of sleep? We don’t know the answer to that,” says Kays. “One of the ways that people have been trying to understand sleep is to study it in a variety of animals and compare the results. Now, with these tiny little sensors, we can let the animals go back to the wild and still get a natural record of their sleep pattern.”

The sensors also indicated when the sloths were dreaming. What were they dreaming about? “A big juicy leaf!” jokes Kays. “If they were having a nightmare, then a harpy eagle!” And that’s no joke. Kays explains that harpy eagles eat sloths. The only way the slowpoke sloth can avoid being eaten by a harpy eagle is to hide, Kays says.

Who Sleeps the Most?

Every animal species requires its own particular amount of sleep. Read the graph to learn more.

Click here to see a video of the scientists who were part of the study as they capture a three-toed sloth and glue a small sensor to its head.

Click on the links below to learn more about sloths:

National Zoo

BBC

How quickly can you solve this jigsaw puzzle? (Faster than a sloth can walk, we hope!)