Road or railway: which is more deadly for the fauna? A puzzling answer from western Romania

Transportation networks have a high negative impact on the fauna, impact considered more pronounced on roads than on railways. However, this fact is difficult to verify because most studies have focused on roads and just a few on railways, and comparative studies are exceptionally rare. Thereby, we set out to compare the fauna mortality on 2 km of road and railway parallel to each other to assess which is more deadly for the fauna. The two transportation networks were studied at the same time (in every month of 2021), in the same place (western Romania), and with the same method (pedestrian surveys). The number of corpses was much higher on the railway, yet the number of taxa and their diversity was higher on the road. On the railway, half of the victims were killed before the year of the study, and, by percentage abundance, over 90% of them belonged to a single taxon (Gastropoda with shells). On the contrary, none of the taxa exceeded 20% on the road. Thus, the answer to our question is complex because at least our data show that neither of the two transportation networks is necessarily more friendly to the environment, but each of them affects the fauna in a different way. The railway can be considered a trap (usually an indirect one) for snails, which cannot escape from it, but it kills other animals too. Although most animals seem to be able to avoid railway mortality, they are nevertheless killed on the adjacent road. The two transportation networks affect the fauna in a complementary way, probably having a cumulative negative effect. Nevertheless, the railway preserves the animal corpses for much longer than the road, which shows that the negative impact of roads is probably underestimated compared to railways.