AT DUSK, the dry savannah of the Kimberley was once alive with the scuttling and foraging of the burrowing bettong, a marsupial whose ''countless numbers'' were marvelled at by early surveyors.
Along with many species of quolls, bandicoots, possums and marsupial rats, the bettongs had thrived for millions of years in northern Australia, surviving ice ages, surging sea levels and human hunters.
But many of these natives are unlikely to survive another decade or two, according to a new report which reveals an abrupt, stunning plunge towards mass extinction in the past few years.
At the 136 sites across northern Australia that have been repeatedly surveyed since 2001, the mammal populations have dropped by an average of 75 per cent. The number of sites classified as ''empty'' of mammal activity rose from 13 per cent in 1996 to 55 per cent in 2009.
''Twenty years ago we would go out and it would be a bonanza of native animals,'' a Charles Darwin University researcher, John Woinarski, said. ''Now we hardly catch anything - it's silent.''
Evidence of encroaching extinction on individual species had been accumulating for decades, but researchers were not necessarily aware that so many species across Australia's north were seeing the same steep declines, Professor Woinarski said.
The report, Into Oblivion: The disappearing native mammals of northern Australia, produced for the environment group The Nature Conservancy, collates many lines of evidence into one of the most comprehensive wildlife surveys undertaken in the region.
As well as years of direct observation, researchers visited Aborigines in Queensland, Western Australia and the Northern Territory with stuffed specimens of various native mammals and tapped local knowledge.
''There used to be caution about the rate of the decline - it could have simply been cyclical - but it has been corroborated and we have a high level of confidence in it,'' Professor Woinarski said.
Among the native species expected to reach the brink of extinction in the coming decade are the northern brown bandicoot, the northern quoll and the brush-tailed rabbit-rat.
On the present trajectories of decline, they will have vanished before 2030.
The burrowing bettong has become extinct on the mainland but has been reintroduced from small populations that survived on islands.
The causes of the population decline varied from case to case, the report said, but they include changes in the size and frequency of fires in northern Australia, predation by feral cats, and the relentless advance of cane toads.
''What's happened is that indigenous people used to burn the country in a mosaic pattern early in the fire season, which provided the food and habitat for these mammals,'' James Fitzsimons, the director of conservation at The Nature Conservancy, said.
''As people have become displaced the fire regime has changed, and now you get really large fires at the height of the fire season.''
The federal government, which was sent a copy of the report yesterday, said the species decline in northern Australia is ''well known and of serious concern''.
It said northern Australia had been identified as a priority for funding under its Caring for our Country program, which oversees work to eradicate invasive species including cane toads.
''The task is a challenging one, compounded by the fact that even in places where there are significant areas of intact
habitat, species loss has been recorded,'' a spokesman for the Environment Minister, Peter Garrett, said.
Source: Sydney Morning Herald