Strain by the train: Patterns of toad fatalities on a Brazilian Amazonian railroad.

Transportation infrastructures are directly responsible for killing billions of animals worldwide. Although the understanding about road impacts have recently increased, the impact of railroads on wildlife has received less attention. The current knowledge concerning the impacts of railroads focuses mainly on large mammals although amphibians might be affected. Our study aims to unravel temporal and spatial patterns of Rhinella toad fatalities on a Brazilian Amazonian railroad, to comprehend how toads are killed and to estimate the magnitude of toad fatalities. Data collection was carried out on foot on an 871-km stretch of the Estrada de Ferro Carajás from 2013 to 2017. We identified different potential causes for fatalities: being run over, desiccated or with barotrauma signs. We estimated a surprisingly high carcass persistence probability of about 38 days. After correcting for the bias from carcass detection and removal, we estimated that approximately 10,000 toads are killed per year (≈ 11 fatalities/km/year). A GLM model showed that toads were more likely to be killed in the dry to wet transition. We identified critical zones of fatalities and prioritized them according to their intensity. The highly critical segments encompass >10% of all fatalities although they cover only 1.5% of the railroad. Our study is the first one to address carcass detection and persistence on railroads and to unravel patterns of fatalities of an amphibian species in a tropical climate. A better understanding of the patterns of animal fatality on railroads is of fundamental importance to manage and mitigate this impact.