The Health Status and Demographics of Koalas in the Pilliga Region of North-Western NSW in Response to Low Yield Selective Logging (State Forests NSW)

Jeff J. McKee, Rosemary J. Booth, Peter Timms, Jon J. Hanger,  Joanne H. Connolly, David Blyde, John G. Callaghan, Steven J. Phillips and Rod Kavanagh

Disease prevalence, nutritional status, reproductive success and demographic indices are indicators of population stability.  Changes in these factors may prelude population decline in response to environmental change.  Between October 1997 and October 1998 we measured mortality, morbidity, subclinical disease prevalence, condition scores and reproductive success of 43 wild koalas captured in the Pilliga State Forests and monitored status changes in 32 of these animals (study group) that were radio-tracked over that period.  Half of the study group resided in areas that were subject to selective logging of Callitris glaucophylla carried out between February and August 1998 (treatment group) while the remainder resided in adjacent unlogged areas (control group). Baseline data derived from the study group includes physiological, morphometric and demographic indices that indicate a relatively healthy population with a high turnover compared to southern and coastal koala populations.  Comparative results showed a significant decrease in the health and condition status of the study group over time but resolved no difference between the status of the treatment and control groups. Longevity was estimated from the age class of observed mortalities and from the age class of 23 skulls collected from the study region. The overall mortality rate was 25% (8/32). The mortality rate in the treatment group was 31% (5/16) with 80% (4/5) of these occurring after logging commenced while mortality in the control group was 19% (3/16) with 67% (2/3) occurring before logging commenced. The possible reasons for the observed differences in mortality rates are discussed. Chlamydia spp., Cryptococcus neoformans, and koala retrovirus (KoRV) infection prevalence rates are reported along with the prevalence of clinical disease associated with these organisms.  In addition to fire and predation, other factors contributing to morbidity and mortality in this population include high ambient temperatures in the summer and the prevalence of Tiger Pear Opuntia aurantica, an exotic cactus.