Wildlife Research Wildlife Research Society
Ecology, management and conservation in natural and modified habitats
RESEARCH ARTICLE

Monitoring indicates rapid and severe decline of native small mammals in Kakadu National Park, northern Australia

J. C. Z. Woinarski A B E , M. Armstrong A , K. Brennan A , A. Fisher A , A. D. Griffiths A , B. Hill A , D. J. Milne A , C. Palmer A , S. Ward A , M. Watson A C , S. Winderlich D and S. Young A
+ Author Affiliations
- Author Affiliations

A Department of Natural Resources, Environment, The Arts and Sport, PO Box 496, Palmerston, NT 0831, Australia.

B School for Environmental Research, Charles Darwin University, Casuarina, NT 0909, Australia.

C Present address: PO Box 601, Jabiru, NT 0886, Australia.

D Kakadu National Park, PO Box 71, Jabiru, NT 0886, Australia.

E Corresponding author. Email: john.woinarski@nt.gov.au

Wildlife Research 37(2) 116-126 https://doi.org/10.1071/WR09125
Submitted: 22 July 2009  Accepted: 3 February 2010   Published: 16 April 2010

Abstract

Context. Australia has a lamentable history of mammal extinctions. Until recently, the mammal fauna of northern Australia was presumed to have been spared such loss, and to be relatively intact and stable. However, several recent studies have suggested that this mammal fauna may be undergoing some decline, so a targeted monitoring program was established in northern Australia’s largest and best-resourced conservation reserve.

Aims. The present study aims to detect change in the native small-mammal fauna of Kakadu National Park, in the monsoonal tropics of northern Australia, over the period of 1996–2009, through an extensive monitoring program, and to consider factors that may have contributed to any observed change.

Methods. The small-mammal fauna was sampled in a consistent manner across a set of plots established to represent the environmental variation and fire regimes of Kakadu. Fifteen plots were sampled three times, 121 plots sampled twice and 39 plots once. Resampling was typically at 5-yearly intervals. Analysis used regression (of abundance against date), and Wilcoxon matched-pairs tests to assess change. For resampled plots, change in abundance of mammals was related to fire frequency in the between-sampling period.

Key results. A total of 25 small mammal species was recorded. Plot-level species richness and total abundance decreased significantly, by 54% and 71%, respectively, over the course of the study. The abundance of 10 species declined significantly, whereas no species increased in abundance significantly. The number of ‘empty’ plots increased from 13% in 1996 to 55% in 2009. For 136 plots sampled in 2001–04 and again in 2007–09, species richness declined by 65% and the total number of individuals declined by 75%. Across plots, the extent of decline increased with increasing frequency of fire. The most marked declines were for northern quoll, Dasyurus hallucatus, fawn antechinus, Antechinus bellus, northern brown bandicoot, Isoodon macrourus, common brushtail possum, Trichosurus vulpecula, and pale field-rat, Rattus tunneyi.

Conclusions. The native mammal fauna of Kakadu National Park is in rapid and severe decline. The cause(s) of this decline are not entirely clear, and may vary among species. The most plausible causes are too frequent fire, predation by feral cats and invasion by cane toads (affecting particularly one native mammal species).

Implications. The present study has demonstrated a major decline in a key conservation reserve, suggesting that the mammal fauna of northern Australia may now be undergoing a decline comparable to the losses previously occurring elsewhere in Australia. These results suggest that there is a major and urgent conservation imperative to more precisely identify, and more effectively manage, the threats to this mammal fauna.


Acknowledgements

Many people have helped with this study. In particular, we thank Miki Ensbey, Riikka Hokkanen, Jenni Low Choy, Lindley McKay and Alistair Stewart for major contributions to fieldwork. We thank the many Parks Australia staff who assisted with logistics, permission and sampling, notably including Rob Muller, Kathie Wilson, Tida Nou and Trish Flores. We thank Parks Australia, particularly Sarah Kerin, Peter Cochrane, Anne-Marie Delahunt, Rod Kennett and Peter Wellings for their support for this project. We thank Jeremy Russell-Smith, Andrew Edwards and Felicity Watt for providing the initial fire-monitoring framework for this study, and providing fire histories for all plots. We thank Kakadu’s traditional owners and ranger staff for their interest and permissions. The Tropical Savannas Cooperative Research Centre also provided support, and we thank in particular John Childs for his interest in this work. We thank Sarah Legge, four anonymous referees and Piran White for comment on an early version. This project was conducted under Permit A01001 of the Charles Darwin University Animal Ethics Committee.


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