Northern bettongs have been reduced to just two populations in the wild, numbering at most 2,500, and researchers say drastic measures may be needed to save the species.
Northern bettongs now occupy just 145km² split between two locations in Queensland’s Wet Tropics, but just one population is known to be stable.
The final report of the five-year Northern Bettong Project, led by WWF-Australia, recommends the establishment of an insurance population as data indicates populations are veering towards ‘critically endangered’ status.
It’s a timely warning with the Senate due to report on the nation’s extinction crisis, prompted by Australia having the highest rate of mammalian extinction in the world.
Highlighting the importance of northern bettongs, new research from the project team reveals the species plays “an irreplaceable role” in the ecosystem.
When Europeans arrived, these small kangaroo-like marsupials were found along a 1,000 km stretch from Rockhampton through to far north Queensland, with habitat restricted to tall open forest bordering upland rainforest.
Previous research concluded northern bettong numbers had declined dramatically but it was thought they persisted in four distinct population areas - Mt. Windsor, Carbine Tableland, Lamb Range, and Coane Range.
To test this, the project team used 587 sensor cameras to search for the species in nearly 100,000 hectares of the Wet Tropics (18,800 trap nights* generated more than 500,000 photographs to sort).
The team made headlines when northern bettongs were ‘rediscovered’ at Mt. Spurgeon in the Carbine Tableland, after not being seen in the area since 2003.
But there was no trace of them left at Mt Windsor or Coane Range.
This means the number of distinct populations has halved, with northern bettongs now only found at Lamb Range and Mt. Spurgeon.
It’s estimated the species has suffered a decrease in area of occupancy by about 70% - from 500km² to 145km² in the last three decades.
The viability of the Mt. Spurgeon population is unknown; a sensor camera deployed by the project team photographed only three individuals in late 2016 in a very small 5km² area.
Lamb Range appears to be the species’ last stronghold with the team cage-trapping 188 individuals in the woodlands south west of Cairns.
“The good news is that the tropical bettong is stable in their core habitat. Nevertheless, actual numbers are likely to be at most 2,500, which is much lower than the 5,000-10,000 estimated in their original “endangered” status listing on the IUCN Red list,” said JCU researcher Dr Sandra Abell who managed the science projects for the team.
Further threats abound. Feral cats were detected at 40% of 11 key areas surveyed in the Wet Tropics, and cattle and feral pigs at 80% of areas.
Cats can prey on bettongs, pigs can compete for food, and pigs and cattle may be having an impact by altering habitat.
The species has also suffered from the loss of Indigenous fire regimes which helped maintain the open woodlands the northern bettong relies upon.
To make matters worse, climate change is likely to further alter habitat, affect seasonal food availability, and exacerbate existing threats from fire and feral predators.
Although the Lamb Range population is considered stable, modelling predicts that if cat predation were to increase by 60%, northern bettongs could be wiped out at Lamb Range in less than 10 years.
“We must protect our remaining bettongs by conserving and restoring woodlands, controlling pests, and using recommended fire management to maintain and enhance their habitat,” said WWF-Australia’s Senior Manager for species conservation Tim Cronin.
“Establishing an insurance population, free from pests, would also give the species a chance if there was a disaster at Lamb Range. But this would need to be managed very carefully.
“It’s not too late for the northern bettong, but our window of opportunity for action is closing fast,” Mr Cronin said.
Project team member Susan Nuske, one of the two students who were awarded their doctoral degrees on this project by James Cook University, has shed new light on their crucial role in the ecosystem.
Truffles help trees absorb nutrients in the poor soil and bettongs eat truffles and spread their spores.
Dr Nuske’s PhD research analysed truffle DNA in droppings. She found that northern bettongs had 77 unique species of truffle in their droppings, that were not eaten by other mammals.
“By eating so many unique species, the northern bettong plays an irreplaceable role in spreading truffle fungi. This role is not fulfilled by other fungi-eating mammals in the same forest.
“Our analysis suggests that this food web is sensitive to the extinction of mammals like the northern bettong,” Dr Nuske said.
Without northern bettongs, the diversity of truffles could shrink, possibly harming the trees’ and ecosystem diversity in general.
The Northern Bettong Project is a collaboration between WWF, James Cook University, traditional owners and the Queensland Government.
The Project was funded under the Australian Government’s National Landcare Program.