Use of agricultural fields by Natterjack toads: Implications for pesticide exposure

Land sharing conservation strategies might not work if wildlife is exposed to plant protection products. Plant protection products are used to protect crops against harmful organisms yet they can also have unwanted side effects on non-target organisms. Amphibians are one group of non-target organisms for which there is evidence that plant protection products can have negative effects on individuals and populations. Despite much research on amphibian ecotoxicology, not much is known about the exposure of amphibians to plant protection products in agricultural landscapes. Here, we study habitat use and movement behaviour of an endangered amphibian, the Natterjack toad Epidalea calamita, in two study areas in Switzerland. We placed arrays of artificial cover boards in agricultural fields and adjacent non-agricultural habitats and used a photographic mark-recapture approach to track individual toads, both adults and juveniles, during and after the reproductive season in the terrestrial habitat. We used multistate and spatial mark-recapture models to analyse the data. Toads used the agricultural fields during spring and summer and set up their home ranges within the fields but there was a great turnover of individuals. Toad densities were higher in agricultural fields than other habitat types, including a nature reserve suitable for the species. Toads preferred open soils and avoided grassy meadows typical of agricultural set-asides, suggesting that the conservation of the species in agricultural landscapes requires new types of biodiversity promotion areas. The results of the study show that toads use agricultural fields during most of the growing season and are thus likely to be exposed to plant protection products.