Patterns of reptile road-kills in the Vendée region of western France
Road mortalities of two lizard and four snake species were recorded in the Vendée region of western France over a period of four years. Road-kills were more frequent in the foraging snakes Hierophis (= Coluber) viridiflavus and Natrix natrix as well as the lizard Lacerta bilineata, and lower in the small lizard Podarcis muralis and the sedentary snakes Vipera aspis and Natrix maura. Road-kills were found throughout the active year, with differences in size class and monthly frequencies in H. viridiflavus, N. natrix and L. bilineata commencing in June. Pearson rank correlation coefficients revealed a significant positive association between monthly road-kill and monthly live counts of H. viridiflavus and N. natrix, suggesting regular road crossings in these species. Road traffic volume was related to the number of road deaths using regression analysis of the log-transformed data. This gave an allometric equation with an exponent of 0.75, which was not significantly different from 1, the exponent required if road-kills increase in direct proportion to increasing road traffic volume. The highest traffic volume route showed lower than expected mortalities, but fewer numbers of species living in the vicinity. Models of road-kill vulnerability in H. viridiflavus and N. natrix, derived from the integration of size frequencies of road-kill and live distributions, predict high vulnerability in small and large individuals. In lizards, particularly L. bilineata, road basking is probably the main factor determining mortality, in addition to species velocities, traffic volumes, road widths, abundance at the sides of roads, and behaviour and activity patterns.
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