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The Burrowing Bettong (Bettongia
lesueur)
In 1817 the French ship Uranie anchored
off Dirk Hartog
Island in Shark
Bay as part of its exploration of
the west coast of Australia.
Its crew collected a specimen of a small kangaroo unknown to science. It
was subsequently described and named after Charles Le Sueur, the artist and
naturalist on a previous French expedition to the islands in 1802. It
became known as Lesueur's rat-kangaroo Bettongia lesueur. Today it
is more commonly known as the burrowing bettong or boodie.
This species is unique among the kangaroos in
that it shelters underground in burrows or large communal warren systems. Bettongs
are approximately the size of a wild rabbit, are stocky in build and
pugnacious in disposition. They are strictly nocturnal, sheltering during
the day in burrows and foraging widely at night in search of seeds, fruits,
flowers, tubers and roots and succulent leaves and grasses. They will often
climb into low shrubs to feed.
Bettongs are capable of producing three young
per year in captivity. They have a gestation period of 21 days and give
birth to a tiny, unhaired and undeveloped young. Females will then mate
again, on the day after the birth and the resulting fertilized egg remains in
arrested development in the uterus of the mother until the pouch young is
weaned. Pouch life is about 115 days (approximately 4 months). Dominant
males establish a harem of females which they defend vigorously against
other males. Both sexes have well developed dominance hierarchies.
At the time of the French expedition the
burrowing bettong had one of the widest distributions of any species of
kangaroo. Its range extended from the western slopes of the Great Dividing
Ranges in eastern Australia to the west coast, and from Broome
in the tropical north to Albany and Adelaide on the
southern coast. Many of the first explorers encountered and commented upon
the distinctive warren systems of the bettong. These were characterised by
dozens of entrances dug under breaks in surface rock with extensive high
mounds of spoil around. Burke and Wills encountered them in southern New South Wales on their south-north crossing of Australia in 1860 as did Giles when crossing
the great unexplored deserts of central Australia in the 1870s. These
warren systems, now occupied by rabbits, are still recognisable today in
many parts of outback Australia.
Shaded area indicates the former distribution
of the burrowing bettong
The burrowing bettong now survives only as
three remnant populations on off-shore islands: Bernier and Dorre Islands
in Shark Bay and Barrow Island off the north-west coast of Western
Australia; and recently reintroduced populations at Heirisson Prong and
Faure Island in Shark Bay in Western Australia and to a conservation
reserve at Roxby Downs in central South Australia.
The last burrowing bettong on the mainland was
recorded by Europeans at Pingelly in Western
Australia's southern wheatbelt in 1942.
Information from elderly Aborigines recorded in the 1980s suggest that the
bettong may have survived for a further 10 - 20 years in the remote
northern deserts of Western
Australia.
It is likely that bettongs were eliminated
from mainland Australia by a combination of factors: the alteration of the
vegetation understorey by introduced grazers such as sheep and rabbits;
direct competition for food and shelter from rabbits; predation from
introduced species such as foxes and cats; and changes in land-use
practices to either intensive agriculture in the wetter parts of their
range or to grasslands in central Australia dominated by natural fire
regimes rather than ancient fire regimes imposed by Aborigines.
Between 1988 and 1990 CSIRO conducted surveys
of Bernier, Dorre, Barrow, and Boodie
Islands to establish
the size and stability of populations of endangered mammals. Surveys in
1988 and 1989 revealed a population of some 5,000 bettongs distributed
between three islands. Barrow
Island (240 square
kilometres) contained the greatest number with some 3,500 animals.
Subsequent surveys have revealed that these populations fluctuate strongly
in size, building up steadily over several years of average to above
average rainfall and then crashing in drought.
An ambitious plan to return the burrowing
bettong to mainland Australia
began in 1992 with the transfer of animals from Dorre
Island to Heirisson Prong, a
peninsula which juts into Shark
Bay. The project was
a co-operative venture between the local community of Useless Loop, a
mining company Shark Bay Salt Joint Venture, and CSIRO. This group created
a fox and cat-free area of some 1200 hectares on Heirisson Prong. This is
maintained by a predator-proof fence that runs across the peninsula, a 20
km wide buffer zone of reduced predator density to the south of the fence
maintained by poisoning and trapping, and the geography of the peninsula
(long and narrow) which limits recolonisation.
The barrier fence that excludes predators
from Heirisson Prong
In 1999 10 bettongs from the Heirisson Prong
project were transferred to the Roxby Downs Arid Recovery Project in
central South Australia.
They were released into a conservation area of 12 square kilometres and
protected by a predator-proof fence. In June 2002 17 bettongs were
transferred from Heirisson Prong to Faure Island, in Shark Bay, as part of
a non-government conservation effort to restock the island with its
original fauna. Australian Wildlife Conservancy manages a
dozen conservation reserves around Australia.
Adapted from Australian Natural History
(1992) 24:22-23
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