Road mortality in freshwater turtles: identifying causes of spatial patterns to optimize road planning and mitigation
Road mortality of freshwater turtles can be high enough to imperil populations near roads, thus there is a need to efficiently and accurately locate regions of excessive road-kill along road networks for mitigation. Weekly over 2 years, we drove a 160 km highway circuit in northeastern New York State, USA and recorded the location of all detected road-kill of three freshwater turtle species (Chelydra serpentina, Chrysemys picta, Emydoidea blandingii). We then analyzed the spatial dispersion of road-kill and the road and landscape features associated with road-kill locations. Road-kill was most prevalent at a limited number of short road segments, termed ‘hotspots’. The locations of hotspots, as indicated by kernel density analysis, and the peak spatial extent of hotspots (250 m), as indicated by Ripley’s K, corresponded to the locations and average lengths of causeways (road segments with wetlands within 100 m on both sides). Hotspots were located at causeways that were greater than 200 m length and characterized by high traffic volumes, close proximity to water, and high forest coverage. We conclude that freshwater turtle road mortality is spatially aggregated at short, severe hotspots, and hotspot locations can be predicted when the locations of wetlands, traffic volumes, and the land-uses bordering roads are known. Hotspot models using these predictors can locate sites along a road network that are the most promising for mitigation to reduce excessive road mortality and maintain connectivity.