Hot Topic

Northern Australia’s vanishing mammals

Thursday, 12 November 2015  | 

Key Points

  • Many small to medium-sized mammals are rapidly declining in northern Australia, even in very large conservation reserves, and drivers of the decline remain uncertain.
  • There is evidence that predation by feral cats plays a key role, especially when coupled with frequent, high-intensity wildfires, or heavy grazing by domestic stock.
  • Management options are limited, but the high rates of decline demand immediate attempts at mitigation in key habitat (e.g. cat suppression, fire management), supported by continuing research.

Authors: Brett Murphy (Charles Darwin University) and John Woinarski (Charles Darwin University)

The decline of small to medium-sized (35-5500 g) non-flying mammals in northern Australia is one of our most urgent conservation issues. In Kakadu National Park, the site with the most substantial long-term evidence base, populations of many species have collapsed since the 1970s. This pattern has repeated across the north, and only a few high-rainfall regions retain a largely-intact assemblage of mammals.

The threats are uncertain, although there is evidence that feral cats (present in the region since the 19th Century) and altered fire regimes play key roles. Cats may act synergistically with high-intensity fires, which remove ground-level vegetation cover, increasing mammals’ exposure to predation. Recent work shows cats: (1) can rapidly extirpate native rodents in experimental trials; (2) prefer habitats burnt by high-intensity fires, where they hunt more efficiently. There is evidence that frequencies of high-intensity fires increased with the loss of customary Indigenous fire management. Cattle may have similar impacts to fire, removing groundcover and facilitating predation. Other potential drivers, which have received little attention, include: (1) disease; (2) fire-driven reductions in habitat quality (e.g. reduced understorey diversity, abundance of hollow trees and logs).

Research to resolve the threats is key to formulating an effective management response. However, high rates of decline demand immediate attempts to sustain remnant populations. Management trials could focus on: (1) intensive fire management (to maintain long-unburnt habitat, prevent high-intensity fires); (2) cat suppression; (3) improving habitat quality (e.g. removing cattle, providing nest boxes). Many northern islands have retained mammal species that have declined drastically on the mainland, and also offer potential translocation sites. Biosecurity for these islands is critical, and, if cats are present, eradication should be considered.

More on this Hot Topic:

– Link to peer-reviewed article via Austral Ecology –

If you have recently published an update on this topic, please contact the HT author for your research to be considered for addition to the evidence review.

 

Supporting Research

Title
Aims
Braithwaite R. W. & Muller W. J. (1997) Rainfall, groundwater and refuges: predicting extinctions of Australian tropical mammal species. Aust. J. Ecol. 22, 57-67.
To examine how groundwater levels influence the distribution and abundance of mammal species.
Firth R. S. C., Brook B. W., Woinarski J. C. Z. & Fordham D. A. (2010) Decline and likely extinction of a northern Australian native rodent, the Brush-tailed Rabbit-rat Conilurus penicillatus. Biol. Conserv. 143, 1193-201.
Provide an empirically based predictive assessment of the impact of fire frequency on the population persistence of the brush-tailed rabbit-rat (Conilurus penicillatus).
Fisher D. O., Johnson C. N., Lawes M. J., Fritz S. A., McCallum H., Blomberg S. P., VanDerWal J., Abbott B., Frank A., Legge S., Letnic M., Thomas C. R., Fisher A., Gordon I. J. & Kutt A. (2014) The current decline of tropical marsupials in Australia: is history repeating? Glob. Ecol. Biogeogr. 23, 181-90.
We aim to test plausible causes of recent declines in range and determine if mechanisms differ between current tropical declines and past declines, which were in southern (non-tropical) regions.
Frank A. S. K., Johnson C. N., Potts J. M., Fisher A., Lawes M. J., Woinarski J. C. Z., Tuft K., Radford I. J., Gordon I. J., Collis M.-A. & Legge S. (2014) Experimental evidence that feral cats cause local extirpation of small mammals in Australia's tropical savannas. J. Appl. Ecol. 51, 1486-93.
To quantify the effect of predation by low-density cat populations on the demography of a native small mammal.
Lawes M. J., Murphy B. P., Fisher A., Woinarski J. C. Z., Edwards A. C. & Russell-Smith J. (in press) Small mammals decline with increasing fire extent in northern Australia: evidence from long-term monitoring in Kakadu National Park. Int. J. Wildland Fire.
To examine whether recent small mammal declines in Kakadu National Park are associated with frequent large-scale fires of low patchiness.
Legge S., Kennedy M. S., Lloyd R. A. Y., Murphy S. A. & Fisher A. (2011) Rapid recovery of mammal fauna in the central Kimberley, northern Australia, following the removal of introduced herbivores. Austral. Ecol. 36, 791-9.
We present the results of a landscape-scale destocking experiment in the central Kimberley, north-west Australia, examining the potential for faunal recovery following the landscape-scale removal of introduced herbivores.
McGregor H. W., Legge S., Jones M. H. & Johnson C. N. (2014) Landscape management of fire and grazing regimes alters the fine-scale habitat utilisation by feral cats. PLoS ONE 9.
To test the hypothesis that: (1) recently burnt or intensely grazed habitats are preferentially used by cats, and (2) that this relationship would be stronger in areas of high small-mammal abundance.
McKenzie N. L., Burbidge A. A., Baynes A., Brereton R. N., Dickman C. R., Gordon G., Gibson L. A., Menkhorst P. W., Robinson A. C., Williams M. R. & Woinarski J. C. Z. (2007) Analysis of factors implicated in the recent decline of Australia's mammal fauna. J. Biogeogr. 34, 597-611.
To assess whether eight factors thought to be involved in the extinction process can explain the pattern of recent decline in Australia’s mammal fauna.
Murphy B. P. & Davies H. F. (2014) There is a critical weight range for Australia's declining tropical mammals. Glob. Ecol. Biogeogr. 23, 1058-61.
Evaluate whether the 35-5500 g 'Critical Weight Range' applies in monsoonal northern Australia
Oakwood M. (2000) Reproduction and demography of the northern quoll, Dasyurus hallucatus, in the lowland savanna of northern Australia. Aust. J. Zool. 48, 519-39.
(1) Describe the reproductive biology and demography of northern quolls; (2) verify whether male post-mating mortality occurred; (3) describe the proximate causes of mortality in a lowland savanna population.
Price O. F., Rankmore B., Milne D., Brock C., Tynan C., Kean L. & Roeger L. (2005) Regional patterns of mammal abundance and their relationship to landscape variables in eucalypt woodlands near Darwin, northern Australia. Wildl. Res. 32, 435-46.
To determine whether mammals respond postively to heterogeneity in fire regimes and vegetation type.
Woinarski J. C. Z., Armstrong M., Brennan K., Fisher A., Griffiths A. D., Hill B., Milne D. J., Palmer C., Ward S., Watson M., Winderlich S. & Young S. (2010) Monitoring indicates rapid and severe decline of native small mammals in Kakadu National Park, northern Australia. Wildl. Res. 37, 116-26.
To detect change in the native small-mammal fauna of Kakadu National Park, 1996–2009, through an extensive monitoring program, and to consider factors that may have contributed to any observed change.
Woinarski J. C. Z., Burbidge A. A. & Harrison P. L. (in press) Ongoing unraveling of a continental fauna: Decline and extinction of Australian mammals since European settlement. Proceedings of the National Academy of Sciences of the United States of America.
(1) Review the conservation status of Australian mammal species, and chart historical changes in status; and (2) describe the extent of loss of mammal diversity and why that loss has occurred.
Woinarski J. C. Z., Legge S., Fitzsimons J. A., Traill B. J., Burbidge A. A., Fisher A., Firth R. S. C., Gordon I. J., Griffiths A. D., Johnson C. N., McKenzie N. L., Palmer C., Radford I., Rankmore B., Ritchie E. G., Ward S. & Ziembicki M. (2011) The disappearing mammal fauna of northern Australia: context, cause, and response. Conservation Letters 4, 192-201.
To provide a context to, attempt an explanation for, and propose a response to the recent demonstration of rapid and severe decline of the native mammal fauna of Kakadu National Park.
Woinarski J. C. Z., Milne D. J. & Wanganeen G. (2001) Changes in mammal populations in relatively intact landscapes of Kakadu National Park, Northern Territory, Australia. Austral. Ecol. 26, 360-70.
Report changes in mammal abundance between 1986 and 1999 at Kapalga in Kakadu National Park
Ziembicki M. R., Woinarski J. C. Z. & Mackey B. (2013) Evaluating the status of species using Indigenous knowledge: novel evidence for major native mammal declines in northern Australia. Biol. Conserv. 157, 78-92.
To assess the extent and timing of change in mammal status across a broad area of the northern half of the Northern Territory, based on Indigenous ecological knowledge.
Ziembicki M. R., Woinarski J. C. Z., Webb J. K., Vanderduys E., Tuft K., Smith J. G., Ritchie E. G., Reardon T. B., Radford I. J., Preece N., Perry J., Murphy B. P., McGregor H., Legge S., Leahy L., Lawes M. J., Kanowski J., Johnson C. N., James A., Griffiths A. D., Gillespie G., Frank A., Fisher A. & Burbidge A. A. (2015) Stemming the tide: progress towards resolving the causes of decline and implementing management responses for the disappearing mammal fauna of northern Australia. Theyra 6, 169-225.
To describe progress of current research into the northern mammal decline and its causes.