Low-density koala (Phascolarctos cinereus) populations in the mulgalands of south-west Queensland. II. Distribution and diet
Sullivan, BJ, Norris, WM & Baxter, GS 2003, Wildlife Research, vol. 30, pp. 331-338.
In the mulgalands of south-west Queensland, the distribution of a local koala population and their food tree preferences were established through a combination of belt transect and faecal pellet surveys. Findings indicated that distribution is strongly associated with annual rainfall, with greatest abundances in northern and easterly regions of the study area. Faecal pellet analyses showed that the vast majority of the koalas’ diets in the mulgalands was comprised of five different Eucalyptus species.
Sampling sites (149 total) were selected based on vegetation communities, landform class and rainfall zone, with faecal pellet surveys carried out beneath each tree canopy, across a 1 km x 10 m belt transect. Cuticular analysis of faecal pellet material was undertaken to determine preferred koala food trees. As demonstrated by faecal pellet presence, distribution across the four landform classes varied significantly. In rainfall zone 3 (highest rainfall), pellets were collected in 95.2% of riverine sites and 67.1% of sites overall, emphasising a strong easterly distribution. In rainfall zones 1 and 2 (lowest and moderate rainfall, respectively), pellets were present in 8.3% and 31.3% of sites respectively. Of the 22 species identified at sampling sites, 93% of plant material from cuticular analyses could be attributed to just five species. Findings showed that, where a faecal pellet contained a significant proportion of material from a dominant species in one landform class, it rarely contained material from another dominant species.
The study’s overall findings suggest a discontinuity in koala distribution from west to east, yet this is unlikely to be as extreme as reported in previous studies. The decline of other arboreal mammals in this region has been associated with a reduction in refuge sites, coinciding also with low water balance. Such disturbances are also likely to have influenced the contraction of koalas away from more arid areas. This is corroborated by the negligible presence of pellets in rainfall zone 1. Regarding koala diet, results suggest that the most abundant Eucalyptus species across the study region were also those eaten more regularly. As koala defecation occurs 1.5 to 6.5 days after feeding, this study’s method of sampling under Eucalyptus trees is likely comprehensive enough to identify the whole spectrum of species forming their diet. Pellets up to a year old had an almost identical plant composition to those that were fresh, suggesting that diet is limited to a narrow range of species and/or that movement between habitat patches is rare. Contrary to popular belief, koalas were not restricted to riverine sites; 52% of active sites were located in non-riverine communities.
The results of this study confirm previous research to reveal a reduction in koala abundance in semi-arid areas of the mulgalands. Management of populations in these low rainfall environments must consider the relative importance of all vegetation communities, especially those commonly viewed as having little conservation value.
Summarised by Julian Radford-Smith
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