Sensory pollution effects on koala calling behaviour: a preliminary phantom road experiment

Context Sensory pollutants, including anthropogenic noise and artificial lights at night (ALAN), are a by-product of urbanisation. Continued expansion of urban centres and associated road networks pose a significant threat to wildlife, including the iconic and endangered Australian koala (Phascolarctos cinereus). Although roads have immediate effects on koalas through mortality and injury from koala–vehicle collisions, as well as habitat fragmentation where roads form barriers to movement, the indirect impacts of sensory pollutants associated with roads remains understudied and road edge effects can confound evaluation. It is crucial that further investigation on sensory pollution be undertaken to inform future conservation actions and planning decisions for koalas wherever roads intersect their habitat. Aims This study employed an illuminated phantom road experiment to evaluate the effects of sensory pollution (traffic noise and ALAN – street lighting) on the calling behaviour of koalas in south-east Queensland, Australia. Methods We broadcasted traffic noise and ALAN in an otherwise roadless area using an automated system while passively monitoring the soundscape. A tally of koala calls was manually obtained from false colour spectrograms and circular statistics were used to evaluate changes in behaviour. Key results Traffic noise induced koalas to vocalise less or avoid calling, particularly when associated with ALAN. Moreover, calling events decreased in experimental locations after the trials were concluded. Conclusions The illuminated phantom road experiment provided the first empirical evidence that sensory pollution may influence koala calling behaviour at the study site in south-east Queensland. Despite not directly tracking movement, the decrease in calling after the experiment suggest that resident koalas may have temporarily relocated to avoid the pollutants. Implications These findings emphasise the critical need for urban infrastructure planning to avoid development in koala habitat wherever possible. Monitoring roads and identifying hotspots of koala–vehicle collisions and sensory pollution can assist the decision making of where to erect exclusion fences, noise barriers, and under- or overpasses, and control traffic volume and speed, thus limiting the spread of traffic noise and reducing the incidence of vehicle collisions.