RAT-KANGAROOS: Potoroidae

PHYSICAL CHARACTERISTICS

Rat-kangaroos are four-legged marsupial mammals that are smaller than most cats. Marsupial mammals are different from most familiar mammals such as cats, dogs, and horses, which are eutherian (yoo-THEER-ee-an) mammals, meaning they use a placenta in reproduction. A placenta is an organ that grows in the mother's uterus and lets the mother and developing baby share food and oxygen. Marsupial mammals do not use a well-developed placenta. Because of this, they give birth to tiny young that are not physically mature enough to survive on their own. Instead, the young are carried for several months after birth in their mother's pouch, or they are attached to the mother's teats, or nipples, on her underbelly. While they are carried this way, they continue to grow until they have matured enough to fend for themselves.

Rat-kangaroos usually have a head and body length that ranges from about 6 to 16 inches (15 to 42 centimeters). The tails of rat-kangaroos can be nearly as long as their bodies, and range in length from about 5 to 15 inches (12 to 39 centimeters). Rat-kangaroos range in weight from about 0.8 to 8 pounds
(0.4 to 3.5 kilograms). Male and female rat-kangaroos are usually about the same size.

Rat-kangaroos have heads that are long and are usually tapered, with small ears that are either round or slightly pointed. Like all kangaroos, their hind legs are longer and stronger than their front legs. This is because rat-kangaroos use their hind legs to move by hopping. Rat-kangaroos have four toes on each of their back feet, but the second and third toes actually grow together although the claws remain separate. Each of the front feet has five toes, each with a claw. Their second, third, and fourth toes on their front paws are longer than their other front toes, and these longer claws help them dig for food.

The fur of the rat-kangaroo ranges in color from dark brown to gray or light brown. The fur is lighter on the underbelly than on the rest of the body. These animals can use their tails, which usually have fur on them, to curl around objects and hold onto them. This type of tail that can be used to grasp is called a prehensile tail. Female rat-kangaroos have a pouch containing four nipples.

GEOGRAPHIC RANGE

Rat-kangaroos live on the coasts of Australia, especially the southern and eastern coasts. They also live in Tasmania and on a few nearby islands.

HABITAT

Rat-kangaroos live mainly in forests where there are many eucalyptus trees. Some types of rat kangaroos, like the burrowing bettong, live in other habitats, such as sandy areas that have dunes.

DIET

Rat kangaroos are primarily herbivores, meaning that they eat mostly plants rather than animals. They mainly eat the parts of fungi that grow underground. To find this food underground, rat-kangaroos use their well-developed sense of smell to help them know where to dig. They dig using the long, sharp claws on their front paws. Some rat-kangaroos also eat small invertebrates, such as insects. Some also eat grass or fruits.

HOW DID THEY GET SUCH BIG FEET?

Rat-kangaroos have back feet that are longer and stronger than their front feet. Scientists think that the ancestors of kangaroos used to jump up quickly and surprise predators. Animals with bigger back feet had an advantage at hopping higher and faster, which might have helped them to survive. Animals with bigger back feet had a better chance of surviving and having offspring, over many generations the genes for big feet got passed on, and the back feet got bigger and bigger, until they are the large back feet that kangaroos have today.

BEHAVIOR AND REPRODUCTION

Rat-kangaroos are nocturnal, which means they are awake and do most of their foraging (searching) for food at night. Most of the daylight hours are spent sleeping, most often in a nest. They build nests out of grass, leaves, and other plant material. Many species get the plant material to their nests by curling their prehensile tail around it and holding it against their rump to keep it steady as they carry it to their nest.

Female rat-kangaroos give birth to one baby at a time. The baby is born after around three weeks of pregnancy. When it is born, it is blind, hairless, and not able to live on its own. The newborn crawls into the mother's pouch and attaches it to one of the mother's nipples where it remains until it is mature enough to survive outside the pouch. Once the young animal leaves the pouch, it becomes a "young-at-foot." During this stage, it follows its mother around and still suckles, nurses, but it is not allowed to get back in the mother's pouch. After another period of development, the young rat-kangaroo goes off on its own. Rat-kangaroos do not usually live in groups after the young mature.

On the night that the female gives birth, she mates again. The egg that is fertilized during that mating stops developing until just before the young that is in the mother's pouch is almost old enough to leave the pouch. The same night that the young leaves the pouch, the mother gives birth to a new baby that then crawls into the pouch that just recently been vacated. After this new baby is born, the mother will mate again. This cycle continues, which means that there are often four generations of rat-kangaroos together: a mother, a young-at-foot, a young in the pouch, and a developing baby that has not yet been born.

RAT-KANGAROOS AND PEOPLE

Rat-kangaroos are not known to have any particular significance to people.

RAT-KANGAROOS AND FUNGI: HELPING EACH OTHER

Rat-kangaroos eat the parts of fungi that grow underground and contain the spores. Spores are the reproductive part of the fungi, similar to a tiny seed. Rat-kangaroos eat the fungi for energy. When the fungi are digested, the spores become activated and ready to grow. The spores leave the rat-kangaroo's body in its waste and are ready to grow into new fungi. In this way, the spores are spread to new areas. This type of relationship between two species where both gain something and neither is harmed is called mutualism.

CONSERVATION STATUS

Many species of rat-kangaroo have been threatened by the clearing of land for agriculture, by fires, and by the introduction of predators that are not native to Australia. Some species of rat-kangaroo have already gone extinct. The desert rat-kangaroo has not been seen since 1935. It is thought that the broad-faced potoroo has been extinct since around 1875. Many other species of rat-kangaroos, such as the long-faced potoroo, are Endangered, facing a very high risk of extinction. Conservation efforts to protect rat-kangaroos include controlling the number of introduced predators, establishing breeding colonies, and creating protected zones.

NORTHERN BETTONG Bettongia tropica; SPECIES ACCOUNT

Physical characteristics: Northern bettongs are about the size of a rabbit, except that their tails are nearly as long as its head and body combined. The length of the head and body is usually about 15 inches (38 centimeters) and the length of the tail is usually about 14 inches (36 centimeters). Northern bettongs weigh about 3 pounds (1.4 kilograms). The back legs are much larger and stronger than the front legs. The head tapers to a pointed snout, and they have small, slightly pointed ears. The fur on the belly is much lighter in color than the rest of the fur. Female northern bettongs have four nipples and a forward-opening pouch.

Geographic range: The northern bettong lives on the northeast coast of Australia.

Habitat: Northern bettongs usually live in areas of forest that are open and have grass on the forest floor. These areas are often found along the edge of tropical rainforests.

Diet: Northern bettongs, like many rat-kangaroos, eat mainly truffles, a type of fungus that grows underground. It also eats cockatoo grass.

Behavior and reproduction: The young of the northern bettong are born after twenty-one days and are immature, like the young of all marsupials. The young then move into the pouch where they remain for 106 days (about three and a half months) before they are mature enough to live outside the pouch.

Northern bettongs and people: Northern bettongs do not have any known significance to humans, except to the scientists who study them.

Conservation status: Northern bettongs are Endangered, which means that they face a high risk of going extinct in the wild. The main reasons it is endangered are loss of habitat due to clearing of land for agriculture and the destruction of habitat through fires. The red fox, which is not native to Australia, may also prey on the northern bettong, leading to reduced numbers. Conservation measures are being taken through the maintenance of two captive breeding populations of northern bettongs. ∎

FOR MORE INFORMATION

Books:

Triggs, Barbara. Tracks, Scats and Other Traces: A Field Guide to Australian Mammals. Oxford, U.K.: Oxford University Press, 1996.

Woods, Samuel G. Sorting Out Mammals: Everything You Want to Know About Marsupials, Carnivores, Herbivores, and More! Woodbridge, CT: Blackbirch Marketing, 1999.

Other sources:

Berry, Ruth, and Mark Chapman. ABC TV Documentaries: Hypsi: The Forest Gardener Aired: January 16, 2001. http://www.abc.net.au/tv/documentaries/stories/s231600.htm (Web site accessed on June 30, 2004).