Koala

## Cuddly koalas

Have you ever heard someone refer to a koala as a "koala bear?" Well, like bears, koalas are mammals, and they have round, fuzzy ears and look cute and cuddly, like a teddy bear. But koalas are not bears. They are members of a group of pouched animals called marsupials. Marsupials include kangaroos, wallabies, wallaroos, wombats, possums, and opossums. Koalas look soft, but their fur feels like the coarse wool of a sheep. They also seem cuddly, but koalas are wild animals and don't make good pets.

## Why trees?

Koalas are native to southeastern and eastern Australia, living in forests of eucalyptus trees. They are basically sedentary animals that need to sleep a lot to give them time to digest their food. Being on the ground all the time would be a disadvantage, because predators could catch them easily. Instead, they adapted to live way up in eucalyptus trees, rear end firmly planted in the fork of branches, so they can chew leaves and nap all they want to without feeling threatened.

Eucalyptus forests are home, shelter, and food for koalas. The animals are built to live in the crooks of branches: koalas have a reduced tail, a curved spine, and a rounded rear end. But they do travel on the ground when necessary, to get from tree to tree or to a new area.

Koalas have few natural predators, although sometimes a dingo or large owl can take one. The most common direct causes of koala deaths are from motor vehicles and dogs. Koalas are definitely safest high up in trees.

## Get a grip

Koala hands and feet are designed to curl around and hang onto tree branches very effectively. Their hands have two opposing thumbs to increase their grip (we only have one), and sharp claws to dig into bark. The feet have a toe that is really two toes fused together, which they use to groom themselves, and a toe that doesn’t have a claw that acts like a thumb for gripping. Rough, ridged pads on the hands and feet aid their grip and give them traction. Strong arm and shoulder muscles help a koala climb 150 feet (46 meters) to the top of a tree and enable it to leap between branches in the trees.

## Catering to koalas

Koalas are naturally solitary animals that are mostly active at night and spend most of their time napping and eating. Koalas eat only eucalyptus leaves. Eating leaves from one kind of plant may seem boring, but there are more than 600 different kinds of eucalyptus trees and, from a koala’s point of view, each looks and tastes very different! Koalas prefer the leaves of about three-dozen varieties.

Eucalyptus leaves are poisonous to most animals, but koalas have special bacteria in their digestive tract that break down the toxic compounds. They can tell which eucalyptus species are more toxic than others and only eat the less-toxic leaves. Special cheek teeth grind the tough eucalyptus leaves. Koalas don't get many calories from their diet, but they conserve energy by moving occasionally and by sleeping as much as 20 hours each day.

At the San Diego Zoo, koalas are offered fresh branches from several eucalyptus species each day. These picky eaters can then select their favorite varieties. Our koalas eat 1 to 1.5 pounds (454 to 680 grams) of leaves each day.

## Party animal?

Just because they sleep a lot does not mean they are quiet, boring animals. Keepers at the Zoo say that each koala has a unique personality. Koalas make several different vocalizations, from snores to bellows to screams. Our researchers are trying to understand why male koalas bellow. Is it to tell other males to stay away or to invite females to visit? The bellow sounds like a mixture of a motorcycle revving and a pig snorting!

## What's that scent?

Male koalas have a bare patch on the chest where his scent gland is located. The male rubs that spot against a tree trunk or branch to mark it with his special smell. Our researchers want to learn more about this scent gland, too, what makes up the scent, and if it changes during the year. We’ve found more than 35 chemicals that make up the scent. We took samples from the males at different times of the year to see if the scents changed and discovered that male koalas are smelliest in spring, when they would be trying to attract a mate.

## A pouch for a nursery

Female marsupials have a pouch in which they carry their baby, called a joey. Many marsupials, like kangaroos, have a pouch that opens upward, toward their head. But koalas have a pouch that opens toward their hind legs. This adaptation keeps burrowing marsupials like wombats, which are close relatives of koalas, from getting dirt in their pouch when they dig. Although prehistoric koalas eventually stopped burrowing and started living in trees, they still have the primitive, back-facing pouch.

## A challenging start

A koala, like other marsupials, begins life in a very unusual way. When it is born, it is only about the size of a large jelly bean and is not yet fully developed. In fact, a newborn joey can't even see or hear, but it sure can climb! Soon after the joey is born, it uses strong forelimbs and hands to crawl from the birth canal into its mother's pouch. The joey attaches to one of two nipples in this warm, safe place where it drinks milk and grows during the next six months.

Even after it starts leaving the pouch, a joey returns there when it wants to hide or sleep. Sometimes it rides on its mother's belly. After it grows too large for the pouch, the joey climbs onto its mother's back and holds on with strong hands and feet. After about a year, it can live alone in the trees.

Koala joeys learn to eat eucalyptus leaves on their own gradually. At first the joey goes after leaves with its mouth. Its early attempts look like a game of bobbing for apples, with its nose getting in the way and pushing the leaves out of reach! Fortunately, joeys keep trying until they are successful. Eventually they figure out how to grab leaves with their hands and put them in their mouth.