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Threatening processes

The causes and prognoses of different types of fractures in wild koalas submitted to wildlife hospitals

Henning, J, Hannon, C, McKinnon, A, Larkin, R & Allavena, R 2015, Preventative Veterinary Medicine, vol. 122, pp. 371-378.

Fractures, whether caused by cars, dog attacks or falls from trees, regularly result in the death or euthanasia of wild koalas. It is, therefore, important for koala conservation and management to identify patterns and risk factors regarding the prevalence of fractures. Within this study, data collected from over 2000 wild koalas with fractures admitted to south-east Queensland wildlife hospitals were analysed. Head fractures and vehicle collisions were the most common type and cause of fractures respectively.

  The majority of koalas admitted to wildlife hospitals exhibited head fractures (56.7%), with torso fractures being the next most prevalent (13.4%). Hindlimb fractures accounted for 9.3% of admissions whereas 5.6% of the koalas had forelimb fractures. The remaining 15% suffered fractures to more than one part of their body. More male koalas (59.8% of admissions) than female koalas (40.2%) had fractures, and mature adult koalas of either sex made up the vast majority of all admissions (89.7%). Koalas with fractures have poor clinical outcomes, with 63.8% of koalas with fractures being dead upon arrival to a wildlife hospital, and a further 34.2% euthanised as a result. Young koalas were the most likely to be successfully rehabilitated and released. No statistically significant differences between the three clinical outcomes (dead upon arrival, euthanised, or released) and the sex of the koala were found. Vehicle collision was the most common cause of fracture (84.1%), followed by dog attack (9.1%) and falls from trees (3.3%).

  A temporal pattern for admission due to vehicle collision or dog attack was identified. This was between July and November, with a peak in September. This likely aligns with the koala breeding season, when koalas are more likely to be travelling on the ground or across roads to find mates. Head fractures were most likely to be caused by vehicle collision, and this is thought to be because koalas are crepuscular and thus active when motorists are using their headlights, which may startle travelling koalas. Torso and limb fractures were more likely to be caused by dog attack, and this is consistent with the canine predisposition of mauling the abdomen of their prey. More male koalas suffered fractures than female koalas, and this is likely because they have larger home ranges and thus travel more regularly and greater distances. Fractures often result in the death or euthanasia of koalas when they occur in regions close to vital organs or result in dental misalignment, seriously hindering a koala’s ability to eat.

  The data gathered in this study will be useful in guiding future management actions for koala conservation. Specifically, the data indicates the vulnerability of koalas to vehicle collision and dog attack, particularly as a result of habitat fragmentation and development in south-east Queensland.


Summarised by Alexander Hendry


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