Abstract
Populations of the iconic Australian koala are under constant decline. Their deaths are associated with the rapid and extensive urbanisation and fragmentation of koala habitat. Using citizen science data on observed koala mortalities in South East Queensland, we quantified the association between environmental, infrastructural and demographic factors and the two leading causes of koala deaths, vehicle collisions and dog attacks. We achieved this objective using two modelling approaches: a Poisson point process model to identify factors increasing the intensity of a given cause-specific mortality and a case-control design to estimates the odds of a given cause of death compared to all other causes of death.
The intensity of koala deaths (that is, the expected number of koala deaths per square kilometre) from vehicle collisions was negatively associated with distance to primary roads, whereas the intensity of koala deaths from dog attacks was positively associated with dog population density. While these results were expected, the value in these analyses arose from the ability to identify specific areas where there was an excess of cause-specific mortality risk after known risk factors had been accounted for.
The results of this research can be used to develop risk mitigation strategies and to enhance surveillance for dog attacks in high-risk areas, for example by conducting educational awareness programs, promoting registration of dogs and discouraging free roaming of dogs. In a similar manner, in high-risk areas for vehicular collisions, safe over or underpasses can be built to facilitate safe movement of koalas for road crossing or speed limits could be introduced to reduce the likelihood of koala deaths.