Tree use, diet and home range of the koala (Phascolarctos cinereus) at Blair Athol, central Queensland
Ellis, WAH, Melzer, A, Carrick, FN & Hasegawa, M 2002, Wildlife Research, vol. 29, pp. 303-311.
In the area of Blair Athol Coal Mine, central Queensland, daytime tree use, home range and diet was monitored in free-ranging koalas. During the observation period, male and female koalas occupied, on average, 93 and 56 trees respectively and home ranges of 135 and 101 ha. Koalas rarely returned to the same daytime roosting tree and proportional species representation in diet did not reliably reflect tree-roosting behaviour.
Throughout the site, koalas were located by systematic surveys and fitted with collar-mounted radio-transmitters. Movements were monitored between 1994 and 1995 during each season, in four 10-21 day periods. Local diet preferences were determined through faecal pellet examination. To monitor tree re-use, trees in which koalas were sighted were marked individually with tags. Findings showed that koalas rarely returned to the same tree, with individual trees used twice or more times on 189 out of 1551 occasions. Only 30 trees were used by more than one koala. Mean home range size did not differ significantly between either sex or season. Ranked data for tree use and diet showed that relative use of species for daytime roosting did not reflect their relative contribution to diet. Additionally, tree-use and dietary preference was not correlated with leaf moisture of diet species.
The infrequent sightings of tree sharing observed in this study suggests that the majority of social interactions take place nocturnally and/or that such events are uncommon. It is acknowledged, however, that compared to southern koala populations, low density, isolated populations in central Queensland are likely affected by different environmental constraints. As findings did not support a role for roosting trees in social interaction, it is expected that this was a result of high tree availability; or conversely, a manifestation of low population density. In turn, the sharing and repeated use of trees demonstrated in studies on southern koala populations may be an implication of absolute tree density, instead of social dynamics. Considerable disparity in diet and daytime tree use for koalas within the same area suggests that there exist social constraints, whereby individuals are excluded from favourable habitat. Furthermore, as a dissimilarity was observed between the selection of species for diet and daytime roosting, it is likely that some species were sought for non-dietary reasons such as shade. As such, deductions made about diet composition based on daytime roosting inspections are likely to be deceptive, especially in heterogeneous environments where different habitat types are associated with different tree-use/dietary selections.
The findings of this study largely accord with the current literature, yet some differ significantly from the behavioural ecology of koalas reported at southern sites. Ultimately, a finer-scale, more localised approach to koala management is endorsed, in which generalised assumptions of koala ecology are first examined against the population of interest.
Summarised by Julian Radford-Smith
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