Decline causes of koalas in south east Queensland, Australia: a 17-year retrospective study of mortality and morbidity
Gonzalez-Astudillo, V, Allavena, R, McKinnon, A, Larkin, R & Henning, J 2017, Scientific Reports, vol. 7, 42587.
South-east Queensland koala populations have been in decline for several decades. The authors of this study examined a comprehensive database of 20,250 koala admissions into wildlife hospitals in the region between 1997 and 2013 to identify the causes of morbidity and mortality that have contributed to this decline. The results suggest that chlamydiosis, motor vehicle trauma and wasting are the most frequent conditions observed and that they frequently co-occur within individuals.
Among the records, eleven distinct conditions were identified. The most common conditions were chlamydiosis (52% of koalas), motor vehicle trauma (15.5%) and wasting (14.3%). Of koalas presenting with chlamydiosis, symptoms were most commonly urogenital (cystitis 26.8%, bursitis 13.5%) and ocular (conjunctivitis 17.2%). The number of animals presenting with these conditions varied over time. While chlamydiosis consistently occurred in at least 30% of koalas over the study period, the incidence of motor vehicle trauma reduced over time, and the number of emaciated koalas admitted into care increased. Chlamydiosis was frequently observed to co-occur with other conditions. Concerningly, the majority of koalas admitted for injuries resulting from motor vehicle trauma were otherwise healthy. For the three most common conditions presented, a number of geographic hotspots and temporal periods of high risk for these conditions were detected. Some spatial-temporal clusters were observed in which cases of chlamydiosis, motor vehicle trauma and wasting overlapped in the periods 1997-2001 and 2010-2013. Additionally, koalas appeared more vulnerable to mortality during the breeding period of August to October.
The high number of koalas admitted into care due to motor vehicle trauma, as well as some spatial and temporal clustering of traumatic incidents, likely relates to periods of rapid infrastructural change in koala habitat areas. It is especially worrying that the majority of koalas injured by cars were otherwise healthy, as this threat is likely to remove healthy breeding individuals from declining populations, especially during the breeding season. The occasional clustering of chlamydiosis and trauma may reflect either an observation bias in these regions or a true association between disease and injury due to factors such as stress associated with habitat loss.
Identifying the causes of morbidity and mortality in declining south-east Queensland koala populations allows conservation interventions to be directed strategically towards the causes and regions likely to deliver the greatest net benefits. The results of this study indicate that causes of morbidity and mortality are synergistic, with multiple factors interacting to cause population decline.
Summarised by Joanna Horsfall
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