Where wildlife and traffic collide: drivers of roadkill rates change through time in a wildlife-tourism hotspot

Rendall, AR. Webb, V. Sutherland, DS. White, JG. Renwick, L. Cooke, R.

Understanding when and where roadkill is most likely to occur is vital to reducing wildlife-vehicle collisions. However, little is known about how roadkill rates change through time and whether or not the key influences on roadkill also change. Understanding changes in roadkill will facilitate the best implementation of mitigation measures. We aimed to determine how roadkill rates have changed between two distinct time periods and assess whether the spatial and temporal drivers of roadkill rates may have changed: with a view to informing species-specific mitigation strategies.

Roadkill hotspots in 1998-99 versus 2014 on Phillip Island between February and June. The size of dot represents the number of roadkill per segment per year (square root transformed). Yellow outlined circles represent roadkill locations only sampled within the 2014 data.

We assess the spatial and temporal factors that influence road mortalities in two periods (1998-99 and 2014) at the same site for multiple taxa. Bi-weekly surveys were undertaken from February to June 1998 and 1999 and again from February to June 2014. In total 2 479 individual roadkill were recorded throughout the surveys, with 1.59 roadkill per km per month in the 1990s, increasing to 2.39 per km per month in 2014.

The number of roadkill per kilometre per month between February and June 1998-99 (white bars) and 2014 (grey bars). Birds (all*) excludes short-tailed shearwaters

Roadkill rates increased primarily with road speed limit with mortalities peaking at moderate (60 – 80km/h) speeds, however, the structural complexity of roadside vegetation and traffic volume influenced roadkill rates for some species but not others. We show that roadkill rates have changed through time with shifts in both the temporal and spatial influences on these roadkill rates. These changes are likely associated with changes in the abundance of taxa and increase vehicle traffic. The spatial and temporal drivers of roadkill rates were found to be species specific, and although mitigation measures exist, assessment of their efficacy remains a priority.

Roadkill hotspots for different taxonomic groups across Phillip Island between February and June 2014. The size of the dot represents the number of roadkill (square root transformed) for Wallabies (orange), possums (blue) and birds (yellow)

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