Mixed sampling protocols improve the cost-effectiveness of roadkill surveys
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Road mortality due to animal vehicle collisions has serious negative effects on population viability, demanding urgent implementation of mitigation measures where most required. Data from roadkill surveys is generally used to choose the best mitigation measures, but there is a lack of knowledge about the sampling intensity required for surveys to effectively detect roadkill patterns. Improving the cost-effectiveness of road surveys could free up limited resources that, in turn, could be used to obtain a better perception of road impacts and mitigation effectiveness elsewhere. We evaluate the possibility of improving road survey cost-effectiveness by comparing the spatial patterns obtained when using a weekly versus monthly survey and year-round versus seasonal surveys. We analyzed a roadkill dataset, previously collected over 2 years in southern Brazil, and applied two criteria for assessing the effectiveness of two alternative survey protocols: tradeoff between sampling effort and sample size; and similarity in spatial patterns. We found support favoring monthly surveys for those taxa in which roadkill was not markedly temporally clustered, as was the case for larger mammals. However, performing weekly surveys over shorter periods may significantly improve cost-effectiveness for taxa with peaks in mortality if surveys are performed during those periods when roadkill is most likely to occur. We suggest applying a mix of sampling protocols, with intensive surveys during warmer periods for reptiles and other taxa with peak roadkill at these times while, for the rest of the year, a monthly survey could be used to improve detection of rarer species.
KeywordsRoad ecology Road monitoring Sample size Spatial pattern Kernel density estimation Vertebrates Brazil
We would like to thank Lucas Del Bianco Faria, Clara Grilo, Luis M. Rosalino and Luis Borda-de-Água for their suggestions on the first version of this manuscript. AS and AB were supported by the project Estrada Viva—RS and financially supported by Fundação O Boticário de Proteção à Natureza (O Boticário Nature Protection Foundation). The authors have no conflict of interest to declare.
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