Factors influencing the road mortality of snakes on the Manchac Land Bridge in Southeastern Louisiana

Road mortality is a significant threat to population persistence for many wildlife taxa. Snakes are an especially vulnerable group because many species exhibit life history, behavioral, ecological, and morphological characteristics that make them vulnerable to dying on roads, and the negative population consequences associated with road mortality.;I used data from a long-term road survey project to determine how body size, sex, season, and thermal ecologies influence vulnerability to road mortality in the snake assemblage found in the Manchac Land Bridge Area of Southeastern Louisiana. Banded Watersnakes (Nerodia fasciata), Green Watersnakes (N. cyclopion), Western Ribbonsnakes (Thamnophis proximus), Diamondbacked Watersnakes (N. rhombifer), and Eastern Mudsnakes (Farancia abacura) experienced high magnitudes of adult male road mortality relative to other demographics. Western Ratsnakes (Pantherophis obsoletus) exhibited a high magnitude of sub-adult road mortality, and Western Cottonmouths exhibited relatively higher magnitude of adult female mortality. Several species showed distinct seasonal patterns of road mortality risk due to activity. Within samples of adult snakes, male and female T. proximus and P. obsoletus displayed significantly different seasonal patterns of road mortality likely due to differential reproductive pressures. Additionally, N. fasciata, N. cyclopion, and Thamnophis proximus snakes showed distinct seasonal patterns of road mortality risk between body size classes. Investigation into the effect of thermal ecology on road entry revealed that N. cyclopion was active, and thus more likely, to enter the road during warmer periods of the active season than other species. It was also discovered that male and female N. fasciata, N. cyclopion, and Thamnophis proximus diverged in temperature preferences for road entry.;I also conducted a field experiment investigating behavioral responses of five snake species to roads and vehicles and compared these to responses to a human representing a natural predator. Multivariate analysis revealed that snakes exhibited distinct patterns of behavioral response to the three types of stimuli. I also identified significant predator response behaviors in four species that are non-adaptive for surviving road crossings. Failure to recognize vehicles as threats to survival, or employing anti-predator behaviors that are not conducive to successfully crossing roads, increases the negative impacts of roads and traffic on snake populations. Investigations into which species and demographic groups are most susceptible to anthropogenic forms of mortality, and how different phenotypes, behaviors, and ecologies contribute to differential vulnerabilities, are useful for developing conservation strategies that maximize individual survival probabilities and population persistence in disturbed landscapes.