Slow Motion Animals

Part One · Meet the Sloth

A sloth is a furry mammal that spends nearly its whole life hanging in the trees of the rainforest. Sloths live in Central America and South America, where the air is warm and wet all year. There are six kinds, and they fall into two groups: some have two long claws on each front foot, and some have three. A sloth is about the size of a small dog, and it weighs somewhere between eight and seventeen pounds. Their long, shaggy fur makes them look a little like a pile of leaves.

Sloths are famous for being slow, and the fame is well deserved, because they are the slowest mammals on Earth. On the ground, a sloth can take a whole minute to move just a few feet. Its arms are much longer and stronger than its legs, so on flat ground it has to drag itself along on its belly. In the trees, however, it is far more at home, and it can reach almost any branch it wants. Scientists think this slow way of life helps them stay safe, because predators notice movement.

The secret to a sloth's slowness is its food. Sloths eat mostly leaves, and leaves give an animal very little energy. To make the most of every bite, a sloth has a stomach with several parts, and it digests its food extremely slowly. A single meal can take as long as a month to pass all the way through. Because it uses so little energy, a sloth moves slowly and saves its strength for the things that matter. Their bodies are very good at saving energy.

A sloth's claws are curved like hooks and can be several inches long. They work the way hooks work on a coat rack. A sloth can hang by its claws without using much strength, and it can even sleep upside down. Its body is built for pulling and gripping, so even a sleeping sloth can keep hold of a branch. Their grip is so strong that a sloth can hang from a branch for hours without getting tired, even when it is sound asleep.

Hanging upside down all day changes how a sloth's body works. Most mammals have fur that parts along the back and flows toward the belly, but a sloth's fur does the opposite, so rain runs off its body as it hangs. Three-toed sloths can also turn their heads about three quarters of the way around, because they have extra bones in their necks. That helps them look for danger without moving the rest of their bodies. It is a very useful trick for an animal that hangs in the trees.

Part Two · A Slow, Strange Life

A sloth's fur is a tiny neighborhood. Its hairs have small grooves where green algae grow, which gives the sloth a slightly green color. That color helps it blend into the leaves and hide from the large birds that hunt overhead. Special moths, beetles, and other tiny insects also live in the fur, and they do the sloth no harm. A sloth in the wild can seem like a small, slow-moving garden. The algae may even give the sloth a little extra food when it licks its fur.

Many people think sloths sleep nearly all day, but that is not quite true. Sloths in zoos sleep up to about fifteen hours a day. Scientists who fitted wild sloths with tiny brain monitors found that they sleep only about nine or ten hours. The wild sloths were awake much more than anyone expected, and they were simply very quiet and slow about it. Being slow, it turns out, is not the same thing as being lazy. Scientists learned this by watching sloths in the wild.

A sloth does one surprising thing about once a week: it climbs down from its tree. Almost everything else it does happens high in the branches, but when it needs to go to the bathroom, it comes down to the forest floor. It digs a small hole with its short tail, makes its deposit, and covers it up. Then it climbs back up the same tree. Scientists are still working out why sloths take this risky trip. On the ground, a sloth is easier for hunters to spot.

Sloths are also good swimmers. Although they are clumsy on the ground, they can move through water using a slow kind of breaststroke, and they can paddle across a river from one side to the other. A sloth can hold its breath for a very long time, up to about forty minutes, by slowing down its heartbeat. In the water, a sloth is actually faster than it is crawling along the ground. Rivers in the rainforest sometimes flood, and a sloth that is a strong swimmer can cross them.

A baby sloth is born high in the treetops and holds on to its mother's fur from the first day. It clings to her belly for months while she carries it from branch to branch. As it grows, it learns which leaves to eat by tasting the leaves its mother chooses. Sloths usually have just one baby at a time, and the mother raises it alone. When the young sloth is ready, it starts to climb on its own. A young sloth may stay close to its mother for many months.

Thousands of years ago, some of the sloths were enormous. A kind called the giant ground sloth was as big as an elephant and stood tall enough to reach into the treetops. These huge animals lived in the Americas until about ten thousand years ago. Today's sloths are their small cousins, and the next time you see a picture of a sloth, remember that it is related to some of the biggest land animals that ever lived. That makes the sloth a very ancient family.