Other variables
We applied further variables that may influence the occurrence of snakes at each site. In V. graeca habitats, we estimated the cover of bare rock, grass and shrub surfaces in a circle of 1-m radius around points of viper presence and random points. In V. renardihabitats, we recorded the number of rodent burrows in a circle of 1-m radius around points of viper presence and random points as these snakes often use rodent burrows for hiding. In V. ursinii habitats, there were no rocks or shrubs, and rodent burrows were rare and not recorded.