The Life Cycle of Marsupials

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Marsupials, as mammals, have milk-producing glands and suckle their young. They reproduce similarly to nearly all other mammals: One or more eggs, produced internally by the female, are fertilized internally by the male and develop within the female's body. After a period of developmental stages lasting weeks or months, the fertilized egg becomes an embryo, then a fetus, and finally is ready to be born. Marsupials differ because after only a short development period, the young fetus leaves the female's uterus and painstakingly crawls over her abdomen to enter the brood pouch (marsupium). Here the fetus continues its development until it is a fully formed and viable organism ready to take up an external existence.

The female has prepared the way for the fetal animal to move over her abdomen by vigorously licking the surface hairs from birth canal to pouch. Observers had long believed the licking laid down a scent trail of saliva for the fetus to follow to the entrance of the marsupium. Recent studies suggest the licking is performed primarily to cleanse the path to be followed by the fetus.

The marsupium is endowed with nipples or teats—the number varies according to the species from one or two to a dozen or more—which the fetus takes into its mouth. This action causes the teat to swell, thus effectively sealing it into the fetus's mouth. The quality of the mother's milk varies during the development of the young; the milk fat increases with time to enhance the nutrition available to the developing young.

Kangaroos, Wallabies, Wombats, and Koalas

The most familiar and readily recognized Australian marsupial are the kangaroos. They range in size from the seven-foot-tall red kangaroo, which weighs up to 200 pounds, to the slightly smaller gray kangaroo, which weighs up to 165 pounds and may be as much as six feet tall. In both species, the heavy, muscular tail is nearly as long as the body. It serves as a prop when the animal is sitting and helps to balance it when it is fleeing. The kangaroo moves forward by a series of powerful hops at speeds of up to thirty miles per hour. The small front legs are used primarily in holding objects.

Wallabies are medium-sized members of the kangaroo family. For the most part, they feed in open grasslands at night. The body size, from nose to root of the tail, is eighteen to forty-one inches. The tail ranges from thirteen to thirty inches long. Because of their smaller size, wallabies are preyed on to a greater extent by dingoes, feral dogs, and, in years past, the Tasmanian tiger.

Before Europeans colonized Australia and introduced sheep and beef cattle, wombats and kangaroos were the major grazers in the grasslands of the island continent. Although it is a marsupial, the wombat looks nothing like any of the other marsupials. It has been described as resembling a fur-covered barrel with four legs. An adult may weigh up to one hundred pounds and measure four feet in length. It is a burrower, tunneling passageways one hundred feet long, six feet under the earth's surface.

The tunnels help the wombat conserve energy and water, and thus reduce its need for food. Its chief foods include grasses, generally of poorer quality than required by sheep. Thus, wombats are able to survive in areas where sheep do not thrive, but if there is better quality forage available, the wombat becomes a competitor with the sheep. As a result, sheep ranchers do not like wombats. They also do not like the cylindrical, muscular animals because they burrow under fences, damaging the fence lines and opening routes for rabbits.

The rotund wombat is not a very swift animal and many fall easy prey to dingoes and large, feral dogs. The most serious threat to the animals, however, is the automobile. Many wombats are killed on the highways as they amble across the pavement at night in search of water or new grazing.

Along with the kangaroo, the most readily recognized Australian animal is the koala, another marsupial. The koala produces one young at a time. When it is able to spend time out of the pouch, it clings to the female's fur and is carried along with the mother on her foraging expeditions. Much of the adult's time is spent high in the tree-tops, especially eucalyptus, whose leaves are a favorite food of the animal.

The average koala male weighs from fifteen to thirty pounds and is about two feet long. The fur is thick and soft

Comparison of Ecological Functions

Between Placental Mammals of North America

and Marsupial Mammals of Australia

Ecological Function

North America

Australia

Large grazer

American bison

gray kangaroo

Small grazer

cottontail

wallaby

Tree dweller

porcupine

koala

Burrowing grazer

woodchuck

wombat

Glider

flying squirrel

sugar glider

Large carnivore

gray wolf

Tasmanian wolf

Small carnivore

wolverine

Tasmanian devil

and the animals were hunted in the fur trade. The last fur season occurred in 1927, when six thousand koalas were slaughtered. They were part of the aborigine diet and undoubtedly had a strong eucalyptus flavor as a result of their diet of eucalyptus leaves.

Although there is no longer an open season on koalas, the mortality rate is high. Loss of habitat in land clearing is a major cause of its decline. In addition, many are killed by automobiles while crossing roadways. Dingoes and domestic dogs kill many of them and a significant number drown in backyard swimming pools. Pool owners often suspend a rope in the water so that koalas that fall in can climb out.

Tasmanian Tigers and Devils

Most of the marsupials in Australia have maintained a somewhat shaky coexistence with the European settlers. Two, however, have not. The Tasmanian tiger (more commonly called the thy-lacine) was the largest living carnivorous marsupial known. It resembled a large, long dog with a long, stiff tail, and brown fur marked with thirteen to twenty dark brown to black stripes on the rear portion of the body. It was active mostly at night and preyed on small animals and birds. The thylacine also occasionally killed and ate sheep and chickens kept by European settlers. It was a fearsome-looking animal, but it was shy and secretive, avoiding contact with humans.

Thylacine females had a back-opening pouch with three to four young in a litter. Pouch life is presumed to have been about four months. The Europeans feared the thylacine, probably because of its bizarre appearance, its nocturnal habits, and its presumed attacks on domestic animals. A bounty was placed on the animal and it was trapped, poisoned, and shot. The last known thy-lacine died in an Australian zoo in September, 1936. Occasional sighting of thylacines have been reported, but in 1986 the species was declared extinct.

The Tasmanian devil, although it is a relative of the thylacine, differs in a number of ways. Devils are smaller, about two feet long with a tail about one foot long. They weigh up to twenty-six pounds and are heavily built, with a broad head and a short, thick tail. The devil's powerful jaws and strong teeth help it to completely devour its food, bones, fur, and all. It is mainly a scavenger and will eat whatever is available. Wallabies, small mammals, and birds are included in its diet, either captured alive or scavenged as a carcass. It has been suggested that the Tasmanian devil helps maintain countryside sanitation by cleaning up carcasses.

The female devil has a back-opening pouch with four nipples. Since more than four young are born in a litter, the extra young die. On average, about two or three young survive in the pouch.

It is the coloration and behavior of the devil that have given it a fearsome reputation. The fur is black, sometimes marked with white patches, and it makes eerie screeches as it ambles about at night in search of food. At one time the Tasmanian devil was widely distributed on mainland Australia, but in modern times it is restricted to the island of Tasmania, off the southeast coast of the mainland. It is believed that the dingo ousted the devil from the mainland. The Tasmanian devil's population, under government management, appears to be stable.

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