Many threatened Australian mammals suffered significant population decline between 1995 and 2016, according to a new mammal database launched today.

Key points: The most comprehensive mammal database to date shows significant declines in the majority of threatened Australian mammals

The most comprehensive mammal database to date shows significant declines in the majority of threatened Australian mammals Big recoveries were seen in areas with targeted conservation measures

Big recoveries were seen in areas with targeted conservation measures Bushfire toll yet to show up in data

Animals such as koalas and quolls, as well as lesser-known species of native rodent and wallabies are among a suite of mammal species that have shown significant reductions in their populations.

Populations declined by more than a third on average over the 20-year period — but the data also revealed that targeted conservation efforts are working.

The Threatened Mammal Index is compiled from more than 400,000 individual surveys, and contains population trends for 57 of Australia's threatened or near-threatened terrestrial and marine mammal species.

Four years in the making, it is Australia's most comprehensive database to date on population trends in native mammals, and was produced by the Threatened Species Hub in collaboration with government and non-government stakeholders.

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The decline of native mammals is due to a "cocktail of factors" according to John Woinarski from Charles Darwin University, who is a member of the Threatened Species Recovery Hub.

Professor Woinarski said he was not surprised to see the extent of the decline.

"We feared that was the case. Mammals have proven really susceptible to a whole range of factors. We've lost 34 species of native mammal already," Professor Woinarski said.

"Feral cats and foxes are a major factor...and certainly habitat loss is another one."

Despite the losses, conservation efforts are working

Success has been seen in places with conservation measures, such as at the Arid Recovery Reserve in South Australia. ( Supplied: TSR Hub/Nicolas Rakotopare )

But the data also contains a very positive message, according to Elisa Bayraktarov from the University of Queensland, who led the project.

In areas where there were targeted conservations efforts — such as cat and fox-exclusion fences — threatened animal populations increased by an average of nearly 46 per cent during that same 1995 to 2016 period.

"We get really fantastic results where mammals have been monitored at...so called 'safe-haven' places like islands and fenced areas," Dr Bayraktarov said.

"The key message...is that if you invest in conservation management it can pay off."

In some places those threatened mammal populations increased by as much as 500 per cent.

Citizen scientists can add to the index

Species like the northern quoll have been impacted by pests such as cane toads and feral cats. ( Supplied: TSR Hub/Nicolas Rakotopare )

Conservation efforts like safe havens currently only cover about 0.1 per cent of the Australian continent, according to Dr Bayraktarov.

But given the success of those programs, the researchers hope that the index will provide a powerful tool for policy makers to decide where conservation needs to be targeted.

"[It can] inform where they should invest in the future — this index is telling us what species need our help and our investment in recovery," she said.

The Threatened Mammal Index now sits in conjunction with the Threatened Bird Index, which was launched in 2018.

Development of the index was funded by the Australian Government's National Environmental Science Program.

The index is publicly available, and will continue to be updated as more research is conducted.

There are still a further 86 native Australian mammal species listed as threatened or near-threatened for which there is not currently enough available data to determine whether their populations are stable, increasing or decreasing.

Australian sea lions were traditionally hunted for their fur and are still listed as vulnerable, with their populations not observed to be increasing. ( Supplied: TSR Hub/Nicolas Rakotopare )

Dr Bayraktarov and her team are accepting research from the public as well as professional researchers and government organisations, in order to make the index as comprehensive as possible.

"People can contact us at tsx.org.au and and say, 'hey, I've been doing this research on, say, a glider'," Dr Bayraktarov said.

"Citizen scientists can actually provide data as long as the data has been collected in a standardised way at the same site over a consistent period."

Bushfire toll yet to show up in the data

As well as feral pests, other key threats to Australian mammals are habitat destruction and climate change, according to Professor Woinarski and Dr Bayraktarov.

The index doesn't yet include mammal population data from the recent devastating bushfire season, but it's feared there will be even steeper declines in fire-affected regions, Professor Woinarski said.

"There'll be a step-change of declines in many of these species in bushfire-affected areas in south-eastern Australia," he said.

"Firstly there is high mortality in the fires themselves...[and] many of [the remaining] animals are dependent on things like tree hollows which the fires wipe out. Then feral predators move in and the animals have got nowhere to hide."

The index will be updated with that research as soon as the data becomes available, Dr Bayraktarov said.

"What we're doing right now with the team is, we're tracking which of the sites we have in the index have been affected by the fires."

"In a couple of years we'll be able to compare how the fires have impacted."