Factors that drive koala roadkill: an analysis across multiple scales in New South Wales, Australia

Abstract

A challenge to understanding the impacts of roads on koalas is that their effects operate across multiple scales. To determine what conditions underlie koala roadkill, we looked at koala roadkill at two spatial scales – the entire state of NSW, and a local government area (Coffs Harbour) – for three road types (primary, arterial and local). We also subdivided the state data into three regions – coast, tableland and inland – to look at regional differences. Our analyses show that koala roadkill is ubiquitous across the distribution of koalas. Similar numbers of roadkilled koalas were recorded on each road type, but because of the vastly different total length of roads in the three types (local roads 122 755 km; arterial 79 706 km; primary 12 972 km) it is clear that an individual koala is more likely to be killed on a primary road than the other two road types. The pattern shown at the LGA scale is similar to that seen across the state. Habitat type adjacent to a road appears to have little influence on the likelihood of a koala being killed on the road. Mitigation measures can reduce koala roadkill, but there is a need to correctly assess the relative importance of koala roadkill compared with other factors that impact on koala populations when allocating resources to koala conservation. We conclude that roadkill is an ever-present threat which will remove an ever-increasing proportion of decreasing koala populations in NSW.