Bilbies

(Thylacomyinae)

Class Mammalia

Order Peramelemorphia

Family Peramelidae

Subfamily Thylacomyinae

Thumbnail description
Rabbit-sized with extremely large ears, long, thin snout, silky bluish gray fur, powerful front feet with large claws.

Size
Head and body 9–10.2 in (23–26 cm); tail 7.8–11.4 in (20–29 cm). Weight 28–88 oz (800–2,500 g).

Number of genera, species
1 genus; 2 species (one extinct)

Habitat
Arid areas of grassland and shrubs with sparse ground cover.

Conservation status
Extinct: 1 species; Vulnerable; 1 species

Distribution
Western Australia, Northern Territory, southwestern Queensland

Evolution and systematics

The only burrowing members of the Peramelemorphia, bilbies probably evolved separately during the Pleistocene period from other bandicoots.

Taxonomists disputed throughout the twentieth century whether the two species in the Macrotis genus, the greater bilby Macrotis lagotis and the lesser bilby Macrotis leucura, constitute a subfamily Thylacominae within the family Peramelidae, or whether they should receive full family status as Thylacomyidae. Both species show distinctive morphological features including a flattened cranium; broad braincase and narrow snout; forward-pointing rostrum; pear-shaped bullae and unique adaptations of the molar teeth. However, other characteristics, such as reproductive biology, are so similar to other species in the order that doubts continue to be expressed about separation.

The lesser bilby has been declared Extinct by the IUCN: the greater bilby is now commonly referred to as the bilby.

The taxonomy for the greater bilby is Macrotis lagotis (Reid, 1837), Swan River, Western Australia, Australia. Other common names include: English: Greater rabbit-eared bandicoot; French: Grand bandicoot-lapin; Spanish: Cangurito narigudo grande.

Physical characteristics

About the size of a rabbit, with huge ears that earn it the alternative name rabbit-eared bandicoot, the bilby has a very long, thin, pointed snout and an extremely long black tail with a white, crested tip. Its fur, bluish gray above and cream to white underneath, is soft and silky.

The forelimbs are strong, with three clawed and two unclawed toes used for burrowing. In common with many other marsupials, the hind feet lack a first toe.

Distribution

Last recorded alive in 1931, the lesser bilby lived in the sandhill deserts of central Australia. The greater bilby occupied a wide variety of habitats and may have lived over about 70% of the Australian landmass. In the 1890s, one naturalist noted that "it was not unusual for rabbiters, even in the immediate neighborhood of Adelaide (South Australia), to take more bilbies than rabbits in their traps." Today, bilbies are only found in one fifth of their former range and are completely absent from the 386,000 mi² (1 million km²) of South Australia where they were once so common.

The species is still comparatively widespread, with fragmented populations in the Tanami Desert of the Northern Territory; the Gibson and Great Sandy Deserts and Pilbara and Kimberley regions of Western Australia; and isolated areas in southwest Queensland.

Habitat

Until the arrival of European settlers, bilbies were found in a broad range of habitats. Only a small number of habitats were avoided. Rocky terrain was not used because of its unsuitability for burrowing. Places with thick ground cover were avoided too, as these marsupials need great mobility for foraging. Europeans introduced much more significant limitations. Today, bilbies are absent from areas with intensive livestock farming, as well as habitat where foxes and rabbits are present in any significant numbers.

Habitats currently occupied by bilbies fall into two types. In the south of its range, this marsupial lives on rises and ridges among sparse grasses, especially mitchell grass Astrebla and short shrubs. Further north, habitats are more variable. They include acacia woodland, acacia scrub with a spinifex Triodia understory, hummock grassland, shrub steppe, and creek beds. A critical factor in the north is the frequency of bush fires. Where fires occur at least once every 10 years, the amount of ground cover is reduced. Such fires also trigger the germination of plants such as Yakirra australiense, whose seeds can be an important part of the animal's diet.

Behavior

Bilbies are solitary animals. Observed groups appear to gather only in response to available food resources and show no social cohesion. Males show some territoriality by scent-marking, but there are no signs of physical aggression towards other males. Both males and females hold overlapping home

ranges, with the male ranges considerably larger. These home ranges are often temporary in nature, however, since bilbies make regular seasonal movements in response to changing food availability.

The pock-marked arid landscapes of central Australia are testimony to bilby burrowing activity. Each individual digs a number of burrows within its home range to shelter in during the day. There can be as many as 12 spiraling burrows, each up to 10 ft (3 m) long. The entrance is usually at the foot of a shrub or grass hummock, or against the base of a termite mound.

This animal can run surprisingly fast, although in an ungainly fashion, with the tail held up off the ground, the hind

feet moving together and the front feet alternately. It rarely strays more than 330 ft (100 m) from a burrow. A bilby may visit several burrows during the night, before selecting one in which to spend the next day.

Feeding ecology and diet

Emerging from its burrow about an hour after sunset, the bilby is wholly nocturnal, returning well before dawn. It searches for food by using its powerful front feet with long claws to dig numerous small conical holes in the ground up to 4 in (10 cm) deep. The long thin tongue is used to lick up much of the food—between 29 and 90% of its feces consists of earth. The senses of smell and hearing are both crucial in food detection.

This marsupial is omnivorous, with a diet that includes seeds, roots, insects, bulbs, fruit, and fungi. Research shows that individual colonies tend to favor one or two food items over all others, probably in response to their abundance within

a particular habitat. Thus in the Tanami Desert, bilbies consume termites and lepidoptera larvae; in Queensland, seeds, bulbs, and acacia root-feeding grubs predominate at different locations. Bilbies do not appear to drink water; instead, they gain the moisture they need from their food.

Reproductive biology

The polyestrous females are physiologically capable of producing litters at any time of the year, although in some areas rainfall and food availability are limiting factors. Bilbies are polygynous. After mating with a socially dominant male, the female undergoes a gestation of just 14 days, then gives birth to one to three young.

No more than a centimeter in length, the newborn young crawl into the backward-facing pouch, where they will remain suckling on a choice of eight teats for the next 80 days. Even after leaving the pouch, the young will stay in the burrow for a further fortnight. The mother continues to suckle them, while at the same time making nocturnal sorties into the open for food. Although the young then leave the burrow and begin feeding on solid food, they often continue to share their mother's burrows for a short while after gaining independence. The young females attain sexual maturity at five months. Male maturity is unknown. The longevity record for a captive greater bilby Macrotis lagotis is seven years and two months.

Conservation status

The lesser bilby has been declared Extinct. Listed as Vulnerable under both IUCN criteria and Australian legislation, the greater bilby now exists in small, fragmented populations over about a fifth of its former range. Competition for food and nesting burrows with introduced rabbits and predation by introduced foxes are significant factors in the species' decline. Feral cats have also depleted numbers. Intensive cattle and sheep farming have limited available habitat through changes in vegetation cover and damage to the soil structure. A lack of managed burning to reduce ground cover is also implicated in localized extinctions.

Despite such historical losses, a national recovery plan promises a better future for the bilby. Its key targets include managing remaining habitat and monitoring populations, as well as captive breeding and re-establishing bilbies in areas where they occurred previously. At the beginning of the twenty-first century, breeding and release schemes on predator-free islands and special enclosures within protected areas were showing signs of success.

Significance to humans

Formerly important as food and hunted for its fur by aboriginal tribes, this marsupial has gained an iconic status today as a symbol of Australia's threatened indigenous wildlife. Adopted as a mascot by the Commonwealth of Australia Endangered Species Program, the species has gained wider public awareness thanks to a campaign that began in the 1980s to replace the Easter bunny with an Easter bilby. Every Easter, thousands of chocolate bilbies are sold, often with a percentage of the profits channeled back into bilby conservation.

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 Online. Baltimore: John Hopkins University Press, 1995. <http://press.jhu.edu/books/walkers_mammals_of_the_world/marsupialia.peramelidae>

Seebeck, J. H., P. R. Brown, R. L. Wallis, and C. M. Kemper, eds. Bandicoots and Bilbies. Chipping Norton, Australia: Surrey Beatty & 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>

Australian Bilby Appreciation Society. P.O. Box 2002, Range-view, Victoria 3132 Australia. E-mail: [email protected] Web site: <http://www.oze-mail.com.au/~bilbies>

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/>

Derek William Niemann, BA