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Helen Grimm BVMS BSc (Con. Biol.)

A Doctor of Philosophy Thesis

The threatened Western Ringtail Possum (Pseudocheirus occidentalis) and the Common Brushtail Possum (Trichosurus vulpecula):
Aspects of ecology and health in the Geographe region of the southern Swan Coastal Plain, Western Australia.

Supervisors:

  • Dr Kris Warren BSc. BVMS (Hons) PhD, Murdoch University
  • Paul de Tores BSc. Dip.Nat.Res., Department of Environment and Conservation (WA)
  • Assoc. Prof. Michael Calver BSc (Hons) Dip. Ed. PhD, Murdoch University
  • Prof. Ian Robertson BVSc, PhD, MACVSc (Epidemiology), Murdoch University

Dr Grimm’s research examined the ecology and health status of two communities of possums occupying very different habitat types on the southern Swan Coastal Plain. The Western Ringtail Possum (WRP) is classed as ‘threatened (vulnerable)’ by national and international conservation assessments and listed as “fauna which is rare or likely to become extinct” under state legislation. The species is only abundant and secure in a habitat type that is under significant present and future threat from urban development. Beyond urban development, remnant populations of the WRP are often found cohabiting with the Common Brushtail Possum (CBP), a larger and more active animal which occupies a broader ecological niche. Dr Grimm carried out spotlighting, capture and radio-telemetry of possums over two years to examine the population density, home ranges, microhabitat use, survivorship and causes of mortality, and baseline health status of possums of both species. The research complemented the concurrent project of Dr Judy Clarke by providing more detailed information on the general ecology and health of the WRP than was previously available.

Possums involved in the study yielded multiple samples for haematology, serum biochemistry, urinalysis, cloacal microbiology, faecal parasitology, ectoparasites, and serology or PCR assay for evidence of infection by Cryptococcus neoformans, Chlamydophila spp., Leptospira interrogans serovars, and Toxoplasma gondii. While the final analyses of baseline health status have not yet (May 2010) been undertaken, early results from the infectious diseases survey indicate no evidence of endemic infection with any of the micro-organisms surveyed.

The work included investigation and application of kernel density estimation techniques for home range analysis, using the relatively recent and novel likelihood cross-validation method for selection of the smoothing parameter. Dr Grimm identified the strengths and weaknesses of these techniques with respect to possum data, particularly relating to sample sizes and the repeated use of specific diurnal rest sites typical of many marsupials.

A further aspect in which Dr Grimm’s research utilised more sophisticated methodology than previously used for study of these species was the application of Distance sampling techniques to spotlighting surveys. Driven by the conservation implications of disturbance of previously secure populations by land clearing, assessment of the population density of the WRP requires practical, efficient and standardized survey methods. Dr Grimm’s research – together with work done by Dr Judy Clarke, supervisor Paul de Tores, and others – is contributing to the development of suitable survey methods for a species that is cryptic and difficult to assess by traditional mark-recapture. The research produced the most accurate estimates of density of established WRP and CBP populations to date, but also identified some methodological limitations that should be addressed by further research.

With the WRP more vulnerable to natural and anthropogenic threats, identification of any habitat characteristics promoting their security is of special interest. Modelling currently underway is examining features of microhabitat use such as the number of den sites used by each individual, characteristics of tree hollows used by possums of either species and the features of foraging activities observed during nocturnal radio tracking.

Although Dr Grimm’s research predominantly examined the community ecology of both possum species, the health and disease results were utilised by Dr Judy Clarke in her associated research. Dr Grimm’s thesis is currently in preparation and will be produced as a compilation of papers to be published in peer-reviewed journals, with publication anticipated to commence later in 2010.

Publications

Grimm, HL and de Tores, PJ (2009) Some aspects of the biology of the common brushtail possum (Trichosurus vulpecula) and the threatened western ringtail possum (Pseudocheirus occidentalis) in a pine plantation scheduled for harvesting and in adjacent tuart and peppermint woodland near Busselton, Western Australia. Report prepared for the Forest Products Commission, Government of Western Australia.

Conferences

  • Grimm, HL (2009) What the h...! Selection of the smoothing parameter in kernel home range estimation. Annual conference of the Australian Mammal Society. University of Western Australia, Perth. 6-8 July 2009. Presented by HL Grimm.
  • McCutcheon, HL (2007) Infectious disease surveillance in possums in the south west. Annual conference of the Wildlife Disease Association (Australasian Section). Dryandra Woodland, Western Australia. 22-28 September 2007. Presented by HL Grimm (née McCutcheon).
  • McCutcheon, HL and JR Clarke (2007) Health status and translocation success of wild and rehabilitated possums. National Wildlife Rehabilitation Conference. Fremantle, Western Australia. 6-9 August 2007. Presented by HL Grimm (née McCutcheon) and JR Clarke.

Collaborators (positions as of Jan 2010)

  • Dr Mark Krockenberger, Senior Lecturer in Veterinary Pathology, Faculty of Veterinary Science, University of Sydney
  • Professor Peter Timms, Professor of Microbiology, School of Life Sciences, Queensland University of Technology
  • Dr Lee Smythe, Director, WHO/FAO/OIE Collaborating Centre for Reference and Research on Leptospirosis, Queensland Health Department

Acknowledgements

This research was undertaken with financial support provided by the Australian Research Council, the Western Australian Department of Environment and Conservation and the School of Veterinary and Biomedical Sciences Murdoch University.

Photos provided by Helen Grimm

Department of Environment and ConservationAustralian Government | Australian Research Council