Less impacted or simply neglected? Anuran mortality on roads in the Brazilian semiarid zone

Amphibians are among the vertebrates most affected by collisions on highways, although the extent of this impact on amphibian populations is usually underestimated by standard survey methods. Specifically in semiarid regions, where rainfall is highly concentrated and unpredictable, large numbers of anurans disperse to reproduce, increasing the risk of mass mortality. In the present study, we evaluated temporal variation in anuran mortality rates on highways in the Brazilian semiarid zone, and the influence of survey technique on the detectability of roadkill anurans. We monitored stretches of two highways in the Brazilian semiarid zone using vehicular and foot surveys over a one-year period. Anuran mortality was positively related with rainfall and was concentrated at the peak of the rainy period, reflecting the high rates of dispersal occurring during the breeding season. Anurans were detected 25 times more frequently during foot than vehicular surveys, and only relatively larger bodied-sized species were detected during vehicular searches. We conclude that anurans suffer high rates of mortality during short periods of the rainy season in the Brazilian semiarid zone, and, while vehicular searches can sample larger transects more rapidly, although they significantly underestimate roadkill anuran mortality in comparison to foot surveys.