The boodie (Bettongia lesueur), also known as the burrowing bettong, is a small marsupial. It is a fascinating example of the effects of introduced animals on Australian fauna and ecosystems. Once the most common macropodiform mammal on the whole continent, the boodie now only lives on off-lying islands and in a newly introduced population on the mainland at Shark Bay.^[3] This animal, first collected during an 1817 French expedition of the west coast, was named after Charles Lesueur, an artist and naturalist who accompanied a previous French expedition. B. lesueur is known by many common names, including the tungoo, Lesueur’s rat-kangaroo, and the short-nosed rat-kangaroo.^[4]

Taxonomy

The boodie belongs to the family Potoroidae, which includes the rat-kangaroos, potoroos, and other bettongs. Four species make up the genus Bettongia. Also, three subspecies of the boodie exist: Bettongia lesueur graii, the extinct mainland subspecies; Bettongia lesueur nova, an undescribed species on Barrow and Brodie Island; and Bettongia lesueur lesueur.^[5]

Paleontology

In the late Oligocene, fossils of paleopotoroines and potoroines (potoroid ancestors) appear. During the Oligocene, ice buildup on Antarctica resulted in less rainfall on Australia. Rainforests declined, replaced by more arid-tolerant leathery leaf woodlands and reed swamps. This climate shift may have favored a radiation of terrestrial marsupials, including potoroid ancestors.^[6] Fossils of the Potoroidae family appear from the mid-Miocene to Recent sediments.^[7] Subfossil records of the burrowing bettong have been found in West Victoria, western New South Wales, and South Australia.^[8]

Morphology

The boodie is a small, rat-like marsupial with short, rounded ears and a lightly haired, thick tail. This animal has a pointed rostrum and beady black eyes, hind limbs longer than the forelimbs and large hind feet. This bettong is yellow-gray above and light gray below. Its short, dense fur feels soft and woolly. The animal bears a faint hip stripe and a distinctive white tail tip. This tail is weakly prehensile and used to carry nest material.^[8][9] About the size of a wild rabbit, this little marsupial weighs an average of 1.5 kg.^[4] Head and body length is an average of 40 cm.^[8] Little to no sexual dimorphism seems to exist. However, morphology varies among subspecies and between islands.^[10]

In general, a potoroid skull can be separated from a macropodid skull by the presence of well-developed upper canines and large plagiaulacoid (bladelike) premolars. Also unlike macropodids, the squamosal bone widely contacts the frontal. B. lesueur skulls are short and broad with large palatal vacuities, inflated auditory bullae, and short, broad nasals. The mandible is relatively short and deep compared to other relatives. The dental formula for all the modern potoroines is I 3/1 C 1/0 PM 1/1 M 4/4. Molars are bunodont and quadrate, and the premolars have 9-11 fine, vertical ridges. Young bettongs have two molars which are replaced by one adult premolar; this event is a good indication of maturity. The post-cranial skeleton of all potoroids has 7 cervical, 13 thoracic, 6 lumbar, 2 sacral, and 22 caudal vertebrae, with 13 pairs of ribs.^[7]

Reproduction

If conditions are good, the Boodie seems to mate throughout the year, probably utilizing a polygynous mating system. Males do not seem to have dominance hierarchies; rather, they defend females against other males. Some females seem to establish associations with other females; whether these contribute to increased reproductive success is unknown.^[7][3] Gestation lasts 21 days, with only one young per litter. Like other marsupial newborns, the newborn is altricial. About four months elapse until weaning.^[4] After young leave the pouch, they take 6-7 months to sexually mature.^[10] Females mate the day after giving birth, and the fertilized egg arrests development until the young is weaned. This is an example of facultative embryonic diapause. In captivity, females are able to bear three young per year.^[4]

Ecology

The boodie once lived in a range of dry subtropical and tropical habitats, from open eucalyptus and acacia woodlands to arid spinifex grasslands. In its current range on the islands, it seems to prefer open Triodia (spinifex) and dune habitats, but will burrow anywhere except places with rocky substrate.^[10] The burrowing bettong eats a variety of food, such as seeds, fruits, flowers, tubers, roots, succulent leaves, grasses, fungi, termites, and marine refuse. It will also raid vegetable gardens. Current populations fluctuate, building up during the years with average or good rainfall and crashing during drought years.^[4][5] These marsupials are known to live at least three years in the wild.^[10]

After colonization of Australia, predators were mainly the introduced red fox and cats.^[4] Some natural predators on the islands include the wedge-tailed eagle and sea eagles; on Barrow Island, monitor lizards appear to be a significant predator.^[10] Before its extinction on the mainland, the boodie served a very important function in the Australian grassland ecosystem. As it foraged, it mixed organic matter into the soil, spreading fungi and seeds. This mixing also increased water absorption into the soil and reduced the combustible material under trees, decreasing the likelihood of fire. These actions helped maintain the balance of trees, shrubs, and grasses. The loss of small, ground foraging animals after European settlement contributed to widespread soil deterioration.^[11] Also, B. lesueur may have helped to thin woody weeds on rangeland by browsing shrubs growing after fires.^[12]

Behavior and physiological attributes

B. lesueur is very vocal, communicating through grunts, hisses, and squeals.^[8] It shelters in underground burrows, the only macropodiform to do so.^[3] Burrows vary from simple tunnels to complex networks with multiple entrances and deep, interconnecting tunnels. These elaborate burrows, or warrens, have been seen having from 4 to 94 entrances.^[8] Warrens are communal, housing an average of 20-40 bettongs. Bettongs appear to switch warrens from time to time, though each has one or two preferred warrens. During the day in the warrens, they form groups of one male and one or many females; males never share warrens with other males. Some of the female-female groups seem to be mother-daughter associations. However, individuals seem to forage alone, showing none of the day-range group associations.^[3][10]

The boodie is nocturnal, sheltering during the day in burrows and foraging widely at night for food.^[4] Locomotion is mainly with the hind legs. The forelimbs are used for support when the boodie is stationary.^[8] This bettong exhibits a slow gait and fast gait. The fast gait (or bipedal hop) is characteristic of the macropodiforms and uses only the hind limbs, with the forelimbs held close to the body and tail acting as a counter-balance. The slow gait (or quadrupedal crawl) is used during foraging and other unstressed times.^[7] Nighttime movement is usually fairly limited, averaging less than 200 m. However, researchers have measured this marsupial traveling 2.2 km searching for food. One individual tracked on Barrow Island traveled 5 km.^[10] B. lesueur uses scent to locate food, which it digs up with the claws on its strong forelimbs.^[5] The boodie will even climb into low shrubs to find food.^[4] Demonstrating little interspecific interactions, bettongs are apparently undisturbed by run-ins with other non-predators.

Bettong digestive systems are characterized by a very large sacciform forestomach, a tubiform forestomach with limited sacculation, and a small hind stomach. The hind gut has a well-developed, simple cecum. Like many macropodiforms, bettongs have foregut fermentation. Daily water intake is only about 3% of its body weight. B. lesueur seems to have renal adaptations to conserve water, which is important in its arid and semi-arid habitats.^[7]

Conservation

Researchers have proposed many possible causes for the boodie's decline on mainland Australia, which began once Australia was colonized. Nineteenth century colonists killed boodies, considering them a destructive garden pest. As ranches spread over the grasslands, livestock grazing reduced vegetation cover, shrinking the rat-kangaroo's habitat. Also, introduced species such as foxes, cats, and rabbits took a severe toll on the boodie, especially on islands. Rabbits competed with them for food and shelter, and the foxes and cats became their major predators. The theory that rabbits compete with boodies for food has been disputed in a study done in 2002 ^[13] although further investigation is needed. Finally, the Aboriginals maintained certain fire regimes, and when these ceased, the habitat probably changed.^[4] By the 1960s, all the boodies on the mainland were extinct.^[5]

Once present in all mainland states except Queensland, the boodie survived on three remnant populations on small offshore islands. These islands include Bernier and Dorre Islands in Shark Bay and Barrow Island off the northwest coast of Western Australia. The marsupial was listed on the 2006 IUCN Red List as Vulnerable due to acute restriction of its area of occupancy to less than 100 km². In 2008 however, due to successful conservation efforts both by government agencies and the private sector, boodies have been listed on the 2008 IUCN Red List as Near Threatened, as its range and population have increased, and are still increasing. Newly established populations included Herrison Prong on mainland Shark Bay by the DEC, as well as Faure Island, Scotia Sanctuary, and also Yookamurra Sanctuary, which were etsablished by the Australian Wildlife Conservancy.

References

Tim Flannery (2007). Chasing Kangaroos: A Continent, a Scientist, and a Search for the World's Most Extraordinary Creature, ISBN 978-0-8021-1852-3