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Judy Clarke BVSc MSc

A Doctor of Philosophy Thesis

Translocation outcomes for the Western Ringtail Possum (Pseudocheirus occidentalis) in the presence of the
Common Brushtail Possum (Trichosurus vulpecula): Health, survivorship and habitat use

Supervisors

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

Dr Clarke’s research examined the health and translocation outcomes of the western ringtail possum, Pseudocheirus occidentalis, a threatened marsupial species (IUCN 2009). Habitat loss due to land clearing for building development threatens the last major coastal population stronghold in and around the town of Busselton in south-west Western Australia. The use of translocation as a management strategy was instigated during the 1990s (de Tores et al. 2004). The aim of Dr Clarke’s project was to investigate factors currently affecting translocation outcomes for the western ringtail possum.

Displaced and rehabilitated western ringtail possums were translocated into three field sites, two of which were baited for fox control. Survival was monitored, causes of mortality were ascertained, and attributes of habitat use were analysed. Each western ringtail possum underwent comprehensive health and disease screening prior to translocation and whenever recaptured for re-collaring. Health, survivorship and habitat use of resident common brushtail possums, Trichosurus vulpecula, were similarly studied at each site.

Mortality rates of translocated western ringtail possums were high. The majority of ringtail possum deaths were attributed to predation, with foxes, cats, pythons and raptors all implicated. Most common brushtail possum mortality was attributable to fox predation. Dr Clarke carried out mark-recapture analyses to investigate which, if any, of a suite of hypothesised factors most influenced post-translocation survivorship of western ringtail possums. The most highly ranked models included pre-release white blood cell counts and/or numbers of common brushtail possums at the release site. Survivorship of western ringtail possums was negatively correlated with each of these factors. The average survival rate of established western ringtail possums was less than half that of resident common brushtail possums.

Health-screening revealed no evidence that infectious disease currently limits translocation success for western ringtail possums. Possums of both species were negative for toxoplasmosis, leptospirosis, salmonellosis and chlamydiosis. Differences between pre- and post-translocation haematological values were found, suggesting that habitat quality or nutrient intake were lower at the translocation sites than in the sites of origin. Mean home range sizes of western ringtail possums were larger than those reported for other coastal populations. Vegetation dominated by peppermint (Agonis flexuosa) was utilised by translocated western ringtail possums where available, and habitat partitioning between the two possum species was observed in some areas. Spotlight surveys revealed presence of low density western ringtail possum populations, derived from previous translocations, at two of the sites.

Complex interactions involving health, predation, habitat quality and interspecific competition influence the success of wildlife translocation programs. The results of Dr Clarke’s project suggest that all these factors, particularly predation, affected translocation outcomes for western ringtail possums during the period of study. Whilst the most efficient use of funds and the best option for the species in its current coastal strongholds is to put greater effort into conserving the western ringtail possum in its natural environment, there could be value in carrying out further experiments to determine whether or not translocation success can be improved through particular management actions. The principles of adaptive management apply both to managing the western ringtail possum in its natural environment and to conducting translocation programs. Possible experimental approaches are outlined in Dr Clarke’s thesis and recommendations for further research are proposed.

References:

de Tores, P.J., Hayward, M.W. and Rosier, S.M. (2004) The western ringtail possum, Pseudocheirus occidentalis, and the quokka, Setonix brachyurus, case studies: Western Shield review - February 2003. Conservation Science Western Australia 5: 235-257
IUCN (2009) IUCN Red List of Threatened Species. Version 2009.1. www.iucnredlist.org.

This thesis is available in Murdoch University's Digital Thesis collection - http://wwwlib.murdoch.edu.au/adt/

Conferences

  • 2009: Clarke J, de Tores P, Warren K, Robertson I, Calver M. Translocation outcomes for the western ringtail possum. Oral presentation: Australasian Wildlife Management Society Annual Conference 30 Nov - 4 Dec, Napier, New Zealand
  • 2009: Clarke J, Warren K, Robertson I, de Tores P, Calver M. Health and translocation success of the western ringtail possum. Oral presentation: Australasian Wildlife Diseases Association Annual Conference 10-16 Dec, The Catlins, Otago, New Zealand
  • 2007: Clarke J, McCutcheon H, Warren K, Robertson I, de Tores P. Health and mortality of translocated western ringtail possums. Oral presentation: Australasian Wildlife Diseases Conference Sept 2007, Dryandra, WA
  • 2007: Clarke J, McCutcheon H. Health status and translocation success of wild and rehabilitated possums. Oral presentation: National Wildlife Rehabilitation Conference July 2007, Perth, WA

Collaborators

  • Veterinary Pathology, Veterinary Clinical Pathology and Veterinary Parasitology departments at Murdoch University
  • Pat Statham of the Tasmanian DPIW Animal Health Laboratory
  • Lee Smythe of the WHO/FAO/OIE Collaborating Centre for Reference and Research on Leptospirosis at Queensland Health Scientific Services
  • Mark Krockenberger of the Koala Infectious Diseases Research Group in the Faculty of Veterinary Science at the University of Sydney
  • Peter Timms of the Institute of Health & Biomedical Innovation, QLD University of Technology

Acknowledgements

This research was undertaken with financial support provided by the WA Department of Environment and Conservation, an ARC Linkage Grant and the School of Veterinary and Biomedical Sciences Murdoch University.

Photos provided by: Paul de Tores, Jennifer Jackson, Helen Grimm, Sophie Arnal, Judy Clarke, Caitlin Prowse

Department of Environment and ConservationAustralian Government | Australian Research Council