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Australian endangered species: Carpentarian Rock-rat

Mammals are disappearing in Australia’s Top End, and we’re not really sure why. This is particularly concerning as northern Australia has a human population density of one person per ten square kilometres…

Mammals are disappearing across northern Australia; the Capentarian Rock-rat is one of them. Damien Stanioch

Mammals are disappearing in Australia’s Top End, and we’re not really sure why.

This is particularly concerning as northern Australia has a human population density of one person per ten square kilometres. It also has extensive and largely natural vegetation cover. The red fox, responsible for much of the mammal decline further south, is absent from the area. Currently we think the declines are a combination of changing fire frequencies, grazing, and cat predation.

The current massive declines echo previous declines in the arid zone.

The Carpentarian Rock-rat (Zyzomys palatalis) is one of these declining mammals. It is one of five species of rock rats, and is only known from five gorges and escarpments on Wollogorang pastoral station near the Northern Territory-Queensland border. It was only described in 1989, with the first specimens collected in 1986.

Together with the Central Rock-rat, it is listed as critically endangered on the IUCN Red List.

It is physically very similar to the other species of rock-rat, and differs mainly in skull characteristics. Its habitat consists of rainforest and vine thickets in rocky sandstone gorges and escarpments.

A female rock-rat with rock-rat ‘pups’ Damien Stanioch

Status

With a highly restricted distribution, the Carpentarian Rock-rat population was estimated to be fewer than 2,000 in 2006. This includes an estimated population of 696 at Moonlight Gorge and 450 at Banyon Gorge. Modelling of rock-rat home range sizes and habitat availability indicates there may be 782 home ranges for the Carpentarian Rock-rat in the area.

Threats

The threats to the Carpentarian Rock-rat are common to other species of small mammal in the Top End: changed fire regimes, and the effects of introduced animals and plants.

Population modelling indicates that the population is highly sensitive to the frequency of hot, late dry-season fires, and these fires could lead to the rat’s extinction within 100 years.

Trampling and grazing of sensitive vegetation by feral herbivores may also cause a decline in the habitat and abundance of Carpentarian Rock-rats.

There is currently no information on cat predation on the Carpentarian Rock-rat, but cats are suspected to cause the decline of other small mammals in the Top-End.

Two young rock-rats Damien Stanioch

Strategy

Due to this species being poorly known, and an almost complete lack of past data of distribution and abundance, targeted research in required to understand the population dynamics of this species. It is even uncertain whether the population has actually declined.

To prevent intense hot fires of the late dry season, it has been recommended to conduct regular, controlled fuel-reduction burns early in the dry season. These are more similar to the burning practises of Traditional Owners, which may be better for the rats.

Establishment of new populations of the species, based on captive breeding, may increase the long-term survival of the species. There were two trial translocation programs to suitable habitat in nearby Limmen National Park, but neither were successful.

We don’t know how many cats are in the area, but adoption of suitable control practises, such as targeted baiting, may be a good idea.

Conclusion

The Carpentarian Rock-rat is a species with a highly restricted distribution, leading to its critically endangered status. Targeted research is required to address the declines of many small mammal species in Australia’s Top End. We need to understand fire and feral species management better.

A greater understanding and implementation of appropriate fire management strategies is needed, as well as effective management of feral species.

Damien Stanioch

Images supplied by Damian Stanioch of the Territory Wildlife Park, which has previously assisted in the Carpentarian Rock-rat recovery plan and captive breeding.

The Conversation is running a series on Australian endangered species. See it here.

Join the conversation

7 Comments sorted by

  1. John Crest

    logged in via email @live.com.au

    Global warming of course.

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  2. Mike Swinbourne

    logged in via Facebook

    Hi Matthew

    Thank you for this article. From your words, the data on this species appears to be almost non-existent, with the causes of its population decline (if there is one) being largely unknown.

    I assume the sensitivity to fire regimes relate to its preferred food supply, which suggests that the different fire regimes may alter seed banks, vegetation regrowth or insects. If this is the case, it might also suggest that it may be sensitive to different grazing regimes, introduced herbivores and invasive vegetation.

    But as you suggest, a lot more work needs to be conducted to fully understand these issues - which is why I am always uncomfortable when well meaning people put forward simplistic solutions to what are really complex and poorly understood problems.

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  3. Peter Ormonde

    Farmer

    Jings - for a split second there I though that with Carpentarian Rock Rat you were talking about our mining magnates... phew. As if that's likely.

    I'm rather concerned that we haven't pinpointed a Key Threatening Process. Statistically the weight is on habitat loss - predation tends to devastate species already in decline. Are there a lot of cats about?

    Are other species in the area in decline? What else has changed over the last century? I'd be starting with the locals myself - good chances…

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    1. Dianna Arthur
      Dianna Arthur is a Friend of The Conversation.

      Environmentalist

      In reply to Peter Ormonde

      Mr O

      "So can I suggest talking to the old locals if you can track some down, find out what else is around the place and what is special that isn't found 500 meters down the road, and work to protect the habitat rather than the species."

      Work to protect the habitat?

      Too much common sense and evidence based reasoning here. Ask the locals? What have they learned in the past 40 to 60,000 years?

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  4. alexander j watt

    logged in via Twitter

    Thanks for this article and I really like the pictures. Those cats are to blame by the sound of it.

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  5. Dion Wedd

    Curator Territory Wildlife Park, Darwin at Territory Wildlife Park

    Hi Mathew, thanks for the article on the CRR. We were heavily involved in captive breeding these little guys and although a seemingly normal looking rodent, captive breeding presented its challenges. They actually shed their skin as an escape mechanism. We often had animals that had large patches of skin missing from their bodies resulting from an altercation with another rat.
    We ceased with the breeding program several years ago when new populations were discovered in the Gulf country. I understand…

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    1. James Whitmore

      Editor at The Conversation

      In reply to Dion Wedd

      Thanks Dion, photo credits were entirely my responsibility. They've been corrected.
      James

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