Importance of Water Availability for Amphibian Roadkill in a Mediterranean Landscape

Roads can negatively impact ecosystems by fragmenting habitats and affecting animal movements and behaviour. One of the major noticeable effects of roads is animal mortality by vehicle collisions, a paramount threat to wildlife, especially for amphibians. In the context of reduced water availability, particularly in the Mediterranean region, amphibians are projected to be one of the most negatively affected animal groups. In this study, we used 14-year road mortality data collected along 120 km of roads, combined with landscape and remote sensing variables, to identify the drivers of amphibian mortality spatial patterns in a Mediterranean landscape, in Southern Portugal. We recorded 5116 carcasses belonging to five amphibian species. Generalised linear models showed that for most of the species, roadkill numbers increased with the decrease in water availability in water bodies. Also, the distance of water bodies to the roads was important in understanding amphibian roadkill patterns, with a general increase in mortality at reduced distances. Land use variables were also significant drivers for amphibian road mortality, with species-specific responses. Roadkill numbers decreased for the Iberian ribbed newt and the fire salamander in agricultural dominated areas. Our results also show an increase in roadkill numbers for the natterjack toad in areas with higher percentage of olive groves, and an opposite response for the fire salamander. We recognize the importance of long-term studies in assessing roadkill patterns, and their value for amphibian monitoring and conservation.