Peramelemorphia (Bandicoots and Bilbies)

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Peramelemorphia

(Bandicoots and bilbies)

Class Mammalia

Order Peramelemorphia

Number of families 2 or 3

Number of genera, species 8 genera; 21 species (18 extant)

No order of marsupials has suffered so badly as a result of European settlement as the Peramelemorphia. Before the arrival of Europeans, bandicoots were plentiful, revered by the aboriginal peoples of Australia, and valued as a source of food by both the aborigines and the native peoples of New Guinea. By the twentieth century, their fortunes in Australia were in steep decline; three species became extinct and at the beginning of the twenty first century, others are still under serious threat of the same fate.

The first Europeans viewed bandicoots with some disdain, purely because of their appearance. Writing in 1805, naturalist Geoffroy wrote "their muzzle, which is much too long, gives them an air exceedingly stupid." Their rat-like shape led to the erroneous name of bandicoot—the Indian word meaning "pig-rat," originally given to the greater bandicoot rat Bandicota indica, of Southeast Asia. Disparaging attitudes have continued into modern times. The word "bandicoot" is still used in the Australian vernacular as a mild term of abuse.

Dismissive attitudes have traditionally been accompanied by scientific neglect. In the classic volume Bandicoots and Bilbies (1990), Lyne noted that of 400 references to bandicoots in scientific journals between 1797 and 1984, more than half were within the final 20 years. Knowledge of this family is still patchy, with the New Guinea species in particular woefully little understood.

Evolution and systematics

The discovery, at the beginning of this century, of an early Eocene (55 million years ago) bandicoot more than twice the age of any fossil bandicoot previously recovered, may help to shed light on an order whose evolution and taxonomy are the object of controversy. Much of the confusion centers around shared physical characteristics with other major marsupial groups.

Some scientists argue that simple dentition suggests that the perameloids evolved from the dasyurids, an order which includes quolls and phascogales. Others claim that the presence of the fused toes of the hind foot shows a closer evolutionary relationship with kangaroos, wombats, and other diprotodonts.

Bandicoots are divided into two families. Species of arid and temperate forest belong to the Peramelidae, a family consisting of four genera and 10 species. Some taxonomists treat the subfamily Thylacomyinae as a complete family. The rainforest bandicoots, found predominantly in New Guinea, sit within the family Peroryctidae, comprising four genera and 11 species.

Physical characteristics

The public perception that "all bandicoots are much the same" is understandable. In appearance, this order has a great deal of uniformity, particularly in Australia, where the species are all roughly rabbit-sized. There is more size variation in New Guinea, where the largest of the Peroryctes is more than

three times bigger than the smallest of the Microperoryctes mouse bandicoots.

Bandicoots have thick-set bodies with a short neck and, in most species, a long, pointed snout. The tail is short, except in the greater bilby Macrotis lagotis, where it is long and brushlike. In the dry-country long-nosed bandicoots Perameles and in bilbies, the ears are large, but the general pattern is for short ears. The front limbs are generally short. The forefeet have powerful, flat claws, used for digging. The hind limbs are longer, with powerful thigh muscles. The hind feet are elongated and, unique among marsupials, the second and third toes are syndactylous, that is, fused together. This fusion is probably an adaptation for grooming. Bandicoots generally move slowly in a bunny hop, with the front and back legs working alternately. They can, however, adopt a fast gallop and some species use their strong back legs to make sudden leaps.

Bandicoot teeth are suited to an insectivorous diet. Although small, they are sharp and the molars are slightly pointed. In common with dasyurids, bandicoots are polyproprodont, possessing four or five pairs of upper incisors and three lower pairs.

Distribution

Bandicoots are found in Australia and New Guinea, including its surrounding islands. Only two species show a range overlap between the two countries—the northern brown (Isoodon macrourus) and rufous spiny bandicoot (Echymipera rufescens). The land masses have been connected intermittently in recent times, suggesting that distribution of species is governed by habitat rather than geographical differences.

In Australia, bandicoots are largely confined to forested coastal strips and offshore islands. The greater bilby found in central-northern parts of the dry interior is the exception. Distribution is more widespread in New Guinea, with both the forested uplands and settled lowlands occupied.

In Australia, distribution was formerly far wider. Among the four arid zone species, the greater bilby is thought to have lived over 70% of the Australian landmass. Three other species—the lesser bilby (Macrotis leucura), pig-footed bandicoot (Chaeropus ecaudatus), and desert bandicoot (Perameles eremiana)—all occupied large parts of the interior, but are now extinct. In 1845, Gould described the southern brown bandicoot (Isoodon obesulus) as "one of the very commonest of Australian mammals."

The range contraction of the northern brown bandicoot in Queensland reflects shrinking distribution of Australian bandicoots under human pressure. Once widespread in the center of the state, it has been forced out of open country by intensive livestock farming and now occupies only narrow strips of land beside rivers.

Habitat

In New Guinea, the habitats of a number of species are linked to altitude. For example, all three Microperoryctes mouse bandicoots are found above 3,500 ft (1,000 m). The high-altitude species are confined to primary rainforest. Among the lowland species of New Guinea and those of Australia, there is evidence that bandicoots can occupy an extremely wide range of habitats.

If there is a linking factor between species of Australia and the New Guinea lowlands, it is their preference for habitats that are temporary by nature. Areas that have been recently burned or cleared, such as light scrub or heath, generally have a wider variety of vegetation and a greater number of invertebrates than more established habitats. These temporary, often ecotonal, habitats are quickly occupied by bandicoots. Such exploitation explains the ready colonization of low-intensity

farmland in New Guinea and suburban towns and cities of Australia. The downside to such opportunism is the bandicoot's reliance on a mosaic of vegetation at different stages of growth. If these become isolated or fragmented, animals are unable to disperse at the point when a particular habitat becomes unsuitable.

Behavior

These marsupials are highly solitary, coming together only to mate. Parental bonds are broken just two months after birth and juveniles show extremely high rates of dispersal. If groups of individuals are seen together, it is purely to exploit a localized food resource.

Males show clear territorial aggression towards each other. During encounters, they mark the ground or vegetation with scent from a gland behind the ear. The two males give warning puffing calls and may chase each other. Rarely, the conflict is resolved by fighting, with both combatants approaching the other raised on their hind legs.

The males have home ranges that are generally several times larger than those of the much smaller females. A single male home range can overlap that of a number of females. The disparity in range sizes is reflected in activity patternsfemales venture into the open almost exclusively to forage for food. Their time out of the nest will be limited further if they still have young in the nest which require suckling. By comparison, males spend some time each night patrolling much larger areas, partly to chase off rival males and also in search of females in estrus.

All bandicoot species studied are nocturnal. Daytime nests vary between species and habitats. Bilbies are the only bandicoots to dig burrows. Other bandicoot species living in open country make their nests among piles of rocks, down rabbit burrows, or in tree holes. They may dig a shallow hole in the ground and cover it with grasses and dead vegetation. Forest-dwelling bandicoots make use of plentiful ground cover by building a heap of grasses, twigs, and humus and hollowing out an internal chamber.

Feeding ecology and diet

Bandicoots are nocturnal, terrestrial foragers, reliant on their strong senses of smell and hearing to detect food. Species studied gain most of their food by using their powerful forelimbs to dig numerous small, conical holes vertically into the

earth or forest floor. Some food is also taken directly from the ground.

All research points to bandicoots being omnivorous. The diet includes a wide range of surface and soil invertebrates, such as ants and termites, beetles and their larvae, earthworms, moths, and spiders. Birds' eggs, small mammals, and lizards are also eaten.

Fungi and fruit are of seasonal importance to forest-dwelling bandicoots. In the few studies of New Guinea species, the large-toothed bandicoot (Echymipera clara) feeds on Ficus and pandanus fruits, while the spiny bandicoot (Echymipera kalubu) has been observed eating a variety of fallen fruit.

Bandicoot dentition, together with a lack of adaptations in the alimentary canal indicate that plant material is eaten selectively, with little fibrous vegetation taken. Seeds and tubers are most often eaten. Omnivorous feeding means that the teeth, sharp and better equipped for a purely insectivorous diet, become flattened with wear.

Reproductive biology

Contact between the males and females of these solitary animals is restricted to mating, when a male will follow the female until she is ready to be mounted. Mating varies between species and location; some bandicoots mate all year round, while others are limited to six or eight months of the year by factors such as day length, rainfall, and temperature. Females are polyestrous and mating is probably either polygynous or promiscuous.

Bandicoot reproduction is unusual in two major respects. They have among the shortest gestation periods of any mammals—just 12.5 days in the case of the northern brown bandicoot. Yet conversely, unique among marsupials, they have an advanced form of placentation that is more akin to that of eutherian mammals with significantly longer gestation periods.

While the embryo first develops with the aid of a yolk sac placenta as is the case with other marsupials, it is nourished in the latter stages of gestation by a chorioallantoic placenta, a more advanced physical attachment between the uterus of the mother and the embryo, that allows the exchange of nutrition, respiratory gases, and excretia. This connection is less sophisticated in the bandicoots however, since they lack villi—the finger-like projections that link the outer membrane of the embryo with the wall of the uterus. Oddly, the umbilical cord remains attached as the young leave the uterus and crawl into the backward-facing pouch. Since the attachment lasts only a matter of hours, the cord's primary purpose at this stage appears to be as a kind of safety rope.

Although the female usually has eight teats, she rarely has more than four young at a time. The young leave the pouch at 49–50 days. Weaning takes around 10 days, by which time the next litter of half inch (1 cm)-long young are ready to occupy the mother's pouch. Bandicoots become sexually mature within four months of birth, but this order's fast reproductive rate is offset by high mortality of the young. Only just over one in 10 of all baby bandicoots will survive long enough to mate. Following maturity, life expectancy is 2.5–3.0 years

Conservation

At the beginning of the twenty-first century, there are some signs that the downward trend in the fortune of bandicoots may at least be slowing. In the previous century, three species had plummeted to extinction even before scientists had gained a clear understanding of their ecology. Today, the IUCN lists (as of 2002) the golden (Isoodon auratus) and eastern barred bandicoot (Perameles gunnii) and greater bilby as Vulnerable and the western barred bandicoot (Perameles

bougainville) as Endangered. Seven New Guinea species are given a Data Deficient rating.

The factors which caused catastrophic declines in Australian bandicoot populations and distribution during the nineteenth and twentieth century are still of paramount significance. Continued intensive grazing by cattle and sheep of former bandicoot habitat over much of the continent ensures that there is no realistic possibility of recolonization without major changes in land management. In Victoria, for example, the hummock grassland of kangaroo and wallaby grass was largely removed in favor of ryegrass and clover to feed grazing livestock. A lack of floristic diversity meant that there was not enough food, or shelter from predators and adverse weather to sustain the population of western barred bandicoots.

Even supposing that livestock grazing could be reduced or eliminated, an added complication is the presence of introduced predators, especially foxes and cats. The arrival of cats on Hermite Island in Western Australia caused the extinction of the golden bandicoot from that island, for example. There is also evidence that bandicoot populations are being suppressed by transmission from cats of toxoplasmosis. Introduced rabbits have also been a major cause of population declines through competition for food and habitat.

While captive breeding programs for greater bilbies and eastern barred bandicoots have proved fruitful, a prerequisite of successful reintroductions into the wild appears to be the exclusion of predators, together with control of rabbits and kangaroos. Exclusion by use of fences can only be effective over very small areas. In some unfenced areas where bandicoots are present, conservation authorities are attempting to limit predation. In Sydney, the National Parks and Wildlife Service began a fox control program in 2001, using the presence of the southern brown bandicoot as an indicator of success.

Colonies of bilbies and western barred bandicoots are being bred at a special facility within the Francois Peron National Park in Western Australia under the Project Eden conservation program, started in 1995. These colonies are supplemented with animals from breeding programs at other agencies such as the Kanyana Wildlife Rehabilitation Centre (bilby, western barred bandicoot) and are slated for the reintroduction phase of the program.

Scientists are still exploring the relative significance of other factors in bandicoot declines. In Western Australia, for example, the extinctions of the pig-footed bandicoot and desert bandicoot are now thought to have been precipitated by the aborigines abandoning traditional burning practices starting in the 1930s. The replacing of mosaic selective burning by uncontrolled wildfires over very large areas left these less mobile species unable to escape.

The conservation of some species is hindered by the fact that they do not live conveniently within protected areas. One fifth of Tasmania consists of nature preserves, yet this does not protect bandicoots, since they live largely on the periphery or outside of these sanctuary zones.

The conservation status of several bandicoot species in New Guinea remains something of a mystery. Seven species are classified by the IUCN as Data Deficient. Partly, this is a reflection of their location in remote and often inaccessible mountain rainforest habitat. But bandicoots are also notoriously difficult to trap. Their preference for natural rainforest food rather than artificial bait means that population monitoring is extremely difficult. Hunting is widespread and common in New Guinea and its islands, but without proper censuses, it is almost impossible to detect whether it is having a deleterious effect.

Significance to humans

The first aboriginal settlers of Australia venerated the bandicoot as one of the creators of life. In their spiritual "dreamtime" stories, they told of Karora, a giant bandicoot who slept in darkness under the earth, until he awoke and gave birth to the first humans from beneath his armpit!

Such reverence did not stop the aborigines from eating bandicoots—they were hunted both for their meat and for their fur. Bandicoots are still an important source of food for some native peoples of New Guinea.

Although killed incidentally by rabbit trappers, bandicoots made little impression on European settlers throughout the nineteenth and much of the twentieth century. The state of New South Wales, for example, first started giving them legal protection only in 1948, by which time three species had become extinct.

Fortunately, a growing perception in Australia of the importance of appreciating and protecting native fauna is now starting to benefit this order. Foremost in the public relations revolution is the endangered greater bilby, whose human supporters launched a sustained campaign from the 1980s onwards to substitute this rabbit-like bandicoot for the Easter bunny as an object of affection in the nation's hearts—an ironically appropriate displacement, given that the introduced rabbit is one of the primary causes of this species' decline.

In well-populated areas of southeastern Australia, where bandicoots come into contact with people, conservation organizations, and state protection departments have made attempts to promote greater tolerance of bandicoots. Residents of suburbia are urged to adopt bush-friendly backyard gardening using native plant species, and are encouraged to maintain close control of family pets at night. However, the bandicoots' habit of digging conical holes in lawns and the risk of transmitting ticks to humans does not always make them the most welcome of cohabitants.

Resources

Books

Hoser, R. Endangered Animals of Australia. Sydney: Pearson, 1991.

Macdonald, D. The New Encyclopaedia of Mammals. Oxford: Oxford University Press, 2001.

Nowak, R. M. Walker's Mammals of the World. Baltimore: Johns Hopkins University Press, 1995.

Seebeck, J. H. Brown, P. R. Wallis, R. L. and C. M. Kemper. Bandicoots and Bilbies. New South Wales: Surrey Beatty and Sons, 1990.

Strahan, R. The Mammals of Australia. Sydney: Australian Museum/Reed Holland, 1995.

Organizations

Arid Recovery Project. P.O. Box 150, Roxby Downs, South Australia 5725 Australia. Phone: (08) 8671 8282. Fax: (08) 8671 9151. E-mail: [email protected] Web site: <http://www.aridrecovery.org.au>

Department for Environment and Heritage. GPO Box 1047, Adelaide, South Australia 5001 Australia. Phone: (8) 82041910. E-mail: [email protected] Web site: <http://www.environment.sa.gov.au>

Environment Australia. GPO Box 787, Canberra, Australian Capital Territory 2601 Australia. Phone: (2) 6274 1111. Web site: <http://www.ea.gov.au/>

New South Wales National Parks and Wildlife Service. 102 George Street, Sydney, New South Wales 2000 Australia. Phone: (02) 9253 4600. Fax: (02) 9251 9192. E-mail: [email protected] Web site: <www.npws.nsw.gov.au/wildlife/factsheets/bandicoot.html>