Koalas are known worldwide as one of the symbols of Australia. Their gray and white fur, broad head, small eyes, large furry ears, and round belly make them appear cuddly like a teddy bear. Koalas range in size from 24 to 33 inches (60 to 85 centimeters) and in weight from 8.8 to 33 pounds (4 to 15 kilograms). This is an unusually large size range. Koalas living in the northern (warmer) part of their range are on average 45 percent smaller than those in the southern (colder) areas. In addition, males can be up to 50 percent larger than females.
Koalas are arboreal, meaning they live in trees. They have strong arms and legs with five toes that end in sharp curved claws to help them climb. The first two toes on the front legs are opposable. This means that these toes, like the thumb on a human hand, can reach across and touch the tip of the other three toes (unlike, for example, a dog paw or human foot, where none of the toes can bend to touch each other). This adaptation helps koalas to grasp branches and climb. The first toe of the hind food is short, broad, and clawless. It is also helpful in gripping branches. As in all members of the order Diprotodontia, the bones of the second and third toes of the hind foot are fused. This condition is called syndactyly (sin-DACK-tuh-lee). The single fused bone, however, has two separate claws. This twin claw is used in grooming.
Koalas do not build nests or live in dens. Their fur protects them from the weather. As a result, the fur of animals living in the colder regions of the range is thicker than that of animals living where it is warmer. In the past, many koalas were killed for their fur. Males have a gland on their chest that produces scent used for marking trees to warn off other males and establish their own individual territory. Females have a backward-opening pouch in which they carry their young. Koalas also have a tiny brain. It is only 0.2 percent of their body weight.
Koalas are found in isolated patches along the eastern coast of Australia from Queensland to Victoria.
Koalas eat only eucalyptus (yoo-kah-LIPtus) leaves. Therefore, they are limited to areas where eucalypts grow. This can range from wet tropical forests to dry open woodlands.
Koalas have strong food preferences. They eat the leaves of about 30 of the 650 species of eucalyptus trees that grow in Australia. Eucalyptus leaves are not an ideal food. They are low in nutrients, hard to digest, and contain toxins (poisons).
In order to digest these leaves, koalas have evolved certain adaptations. They avoid the most poisonous species of eucalypts, and their liver is capable of detoxifying, or making harmless, some of the harmful chemicals in the leaves. They have strong grinding teeth (molars and pre-molars) that grind the tough leaves into a paste. Finally, they have an enormously long cecum (SEE-kum) in which the leaves are digested. The cecum is part of the digestive system. It is a type of sac located where the large and small intestine meet. In the koala, the cecum can be more than 75 inches (2 meters) long. The cecum contains bacteria that help break down the eucalyptus leaves. Koalas get most of the water they need from their diet. However, when fresh water is available, they will drink.
BEHAVIOR AND REPRODUCTION
One reason that koalas can exist on low-nutrient food is that they have developed a lifestyle that allows them to conserve energy. They sleep for up to twenty hours each day, and also spend part of the time that they are awake resting. They are nocturnal animals, feeding mainly at night.
Koalas live alone. Males use the scent gland on their chest to mark certain trees as their own territory. They will fight with other male koalas that come into their home trees. The male’s home territory often overlaps with that of several females. The size of the territory depends on how plentiful the food supply is.
Koalas mate during the cool season in Australia. A dominant male will mate with as many females as he can find. Once mating is complete, the animals go their separate ways, and the male has nothing to do with raising the offspring. Koalas are capable of mating when they are two years old, but generally do not begin to reproduce until they are four or five. Their lifespan is about ten years in the wild, and almost double that in captivity.
A single baby is born after a thirty-five–day pregnancy. The baby is tiny, measuring less than an inch (2 centimeters) and weighing less than 0.02 ounces (0.5 grams). The newborn crawls to its mother’s pouch where it stays for five to seven months. When it is about half a year old, it comes out of the pouch and clings to its mother’s belly or back. During this time, it still nurses, but it also eats vegetable material that has passed through the mother’s digestive system. Scientists believe that in this way the bacteria in the cecum that is needed to digest eucalpytus leaves is passed on from mother to child. The young koala stays with its mother until it is about a year old. By age two it begins looking for its own territory.
KOALAS AND PEOPLE
Aboriginal peoples of Australia hunted koalas for food, as did Europeans when they arrived in Australia. Today koalas are symbols of Australia recognized throughout the world. Their image attracts many tourists, and their image can be found on all types of souvenirs. Very few koalas are sent to zoos outside Australia because of the difficulty in keeping them supplied with fresh eucalyptus leaves.
By the end of the 1920s millions of kolas had been hunted for their fur, and these animals had become extinct in parts of their original range. Intense conservation programs, including protecting habitat, breeding programs, and relocation of some animals, has resulted in a substantial increase in the koala population. There are even some areas where overcrowding is occurring today, leaving the koalas vulnerable to disease and starvation. Today, although there are plenty of koalas, conservationists are concerned about their loss of habitat. The areas in which koalas live are some of the most rapidly developing places in Australia. The Australian Koala Foundation has been a leader in mapping koala habitat and lobbying for its protection.