Roads and other linear infrastructures are among the largest and most visible human-made artefacts on the planet today and represent a threat for both endangered and common species, mainly due to additional mortality from collisions with vehicles. There is strong evidence that additional non-natural mortality affects many species and a growing number of populations could have increased risk of extinction unless effective mitigation actions are applied. At a global scale, Europe is among the regions with highest transport infrastructures density. Between 1970 and 2000 the kilometres of built roads more than tripled in several countries in Europe (EU-15) reaching up to 3 million km of which around 51 500 km consisted of motorways (1.7%). Currently, 50% of the continent is within 1.5 km of transportation infrastructure which may lead to declines in birds and mammals. We urgently need to advance our understanding of how roads affect biodiversity through two steps: 1) identifying which species and regions are more at risk from infrastructures; and 2) determining where those risks result in impacts (loss of biodiversity). Road ecology as a discipline has largely focused on the first step. In Europe, roadkill rates have been estimated for a wide range of vertebrates with millions of casualties detected each year. However, we still lack estimates for all species or areas, even in well-studied regions. The aim of this study is to determine which species are at risk due to roads and where roads can impact population persistence and biodiversity. We focused on bird and mammalian species in Europe as a case study. First, we developed a predictive model of roadkill rates based on diverse species traits which allowed us to predict rates for all European terrestrial bird and mammal species and to map the potential incidence of roadkills. We fitted trait-based random forest regression models separately for birds and mammals to explain empirical roadkill rates. We used all available roadkill rates and the following predictors: species trait data, multiple characteristics of the study (latitude and longitude and survey interval) to account for species abundance and detectability, and taxonomic order to account for evolutionary relationships. Second, we used a generalized population model to estimate long-term vulnerability to road mortality. We estimated ~194 million birds and ~29 million mammals may be killed each year on the European road network. Overall, species with higher roadkill rates differ from those in which roadkill is likely to affect long-term persistence. Simplified models of species traits and wildlife-roads interactions at a macro scale allow a first assessment of the road mortality on wildlife and implications on population’s persistence. This macroecological approach provide guidance for national road planning, support the definition of target areas for further testing at a finer-scale resolution, and ultimately prioritize site-specific areas where mitigation would be most beneficial.
