Occurrence and use of tree hollows by mammals in fragmented and continuous savanna woodlands in Northern Australia

  • Geoffrey Wade Pittman

    Student thesis: Other thesis - CDU


    Previous research suggested the possibility that northern hrushtail possums Trichosurus vulpecula arnhemensis (possum) and black-footed tree-rats Meseinbrioinvs goulthi (tree-rat) may compete for limited hollow availability in patches of woodland. The aim of this study was to examine this possibility by firstly quantifying the densities and dimensions of hollows and hollow-hearing tree characteristics, and the densities of possums and tree-rats in patches and continuous woodland. By comparing the dimensions of hollows preferred by possums and tree-rats between patches and continuous woodland areas, and variation in hollow selection, evidence of limited hollow availability and competition for preferred hollows may he revealed. Specifically I examined the hypothesis: do possums and tree-rats choose significantly different hollow dimensions when hollows are in limited supply?

    Hollow bearing tree (15 ha') densities were approximately equivalent in patches and continuous areas. Possum densities were significantly higher in patches (3 ha') compared to continuous areas (0.6 ha'). Tree-rat densities were equivalent in both areas (0.11 ha'). There were 25 hollow-hearing trees available per animal in continuous areas, and 4 in patches, suggesting a large reduction in potential hollow availability in patches. Possums and tree-rats chose similar hollow dimensions (12 cm and 11 cm entrance width respectively) in trees with similar characteristics in continuous areas and chose significantly different hollow dimensions (11 cm and 6 cm entrance width respectively) in patches. Possums showed significant differences in den selection behaviour in patches, as fewer hollows were used by individuals and sharing of hollows with other possums was significantly greater.

    I conclude that when possum densities are high and hollow availability low, possums and tree-rats compete for preferred hollows. Possums out-compete tree-rats for preferred hollow dimensions, hence tree-rats being the smaller animal are relegated to using smaller hollows outside the range of dimensions that possums can utilise.

    Hollow-bearing tree characteristics used by possums and tree-rats were identified using logistic regression models. The significant tree characteristics; trunk hollows, canopy width and major branch number, were the same for both species. The models can he used to assist identification of potential habitat trees on ground surveys. Estimating the occurrence of hollows from a ground based survey is applicable in savanna woodland because hollows were successfully identified using this method on 78% of occasions.
    Date of AwardJun 2003
    Original languageEnglish
    SupervisorPeter Whitehead (Supervisor)

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