Assessing Brazilian reptiles' road‐kill risks using trait‐based models

Abstract

Reptiles are an understudied group in road ecology, despite evidence of their high vulnerability to road mortality. Recently, trait‐based models have been demonstrated to be valuable tools for explaining and predicting road mortality risks for birds and mammals. The present study aimed to apply such models to reptiles for the first time. We fitted eight random forest regression models, controlling for different survey design variables, to explain 782 empirical road‐kill rates for Brazilian reptiles and selected the best‐performing model to predict road mortality risks for 572 continental species. The results showed that species that are habitat generalists, omnivorous, viviparous, cathemeral, and have intermediate clutch or litter sizes are at a higher risk of being road‐killed. The relationships for other traits included in our models were uncertain, but our findings suggest that population density and species‐specific behavioural responses to roads and traffic may play an important role in road mortality risks. Geographical location and survey design variables (especially sampling speed and sampling time) were more important in explaining the variance of the empirical road‐kill rates than any of the tested ecological and functional traits. Besides adding evidence of the vulnerability of the Amazon region to vertebrate road‐kills, this study highlights some similarities between the relationships identified here and those found for birds and mammals (such as with body mass and habitat breadth). We also corroborate that trait‐based models are useful tools to aid in conservation efforts but indicate that they can be biased by the methodologies used to collect empirical data. Future road‐kill surveys should therefore use methods specifically designed for reptiles and estimate both observer efficiency and carcass removal rates.