Olfactory Repellents in Road Ecology: What We Know and What to Focus on in the Future

Road transport systems kill millions of animals on every inhabited continent each year, and thousands of human lives are lost. Odour repellents (ORE) are a WVC mitigation measure which have been extensively applied across central Europe to prevent or minimise the number of ungulate–vehicle collisions (UVCs). OREs aim to increase the vigilance of ungulates near roads and therefore change their behaviour in areas where vehicle collisions may occur. Despite many scientific papers on the topic of odour repellent effectiveness, a lack of behavioural studies means there is still little understanding of the mechanism of ORE functionality. OREs are applied as an area repellent, so their effectiveness is influenced by multiple factors, and constantly discussed by both academics and the lay public. This paper summarises the state of knowledge about application and effectiveness of odour repellents in road ecology, and suggests research questions to fill information gaps.