Correlates between morphology, diet and foraging mode in the Ladder Snake Rhinechis scalaris (Schinz, 1822)

In many vertebrates, foraging mode (active versus sit-and-wait) is tied to some traits of their natural history such as morphology, type of prey, rate of food acquisition, and survival rate. We explore the correlates between some morphological traits of a Mediterranean colubrid and its feeding ecology and the predation risk, by comparing data on teeth number, tail damage, and diet. A large sample (n = 368) of the Ladder Snake, Rhinechis scalaris is used. The species feeds almost exclusively on endotherms, mainly mammals (nearly 95% of the diet in mass), which set R. scalaris among the most stenophagous snakes in the western Palaearctic. There is also a high percentage of motionless prey in the diet (up to 50% in prey mass), such as nestling birds, mammals and bird eggs. The species is so canalised to a diet based on endotherms that it does not follow the general rule in medium-sized snakes of an ontogenetic dietary shift from ectothermic to endothermic prey; juveniles consumed the smallest endothermic animals: nestling small-mammals. The number of maxillary teeth (mean 15.1), the lowest within the former and large genus Elaphe, is likely related to its trophic specialization. Rhinechis scalaris also faces an elevated risk of predation, something general in active searcher snakes compared to ambush foragers, as revealed by many individuals with damaged tails (19.9%), the highest within the Iberian community of snakes. We conclude from indirect evidence (high predation on stationary prey, many individuals with damaged tails) that the species is an active searcher and that this foraging mode infl uences other natural-history traits (i.e. reproductive habits).