The causes of intraspecific variation in sexual dimorphism in the common grass snake populations, Natrix natrix LINNAEUS, 1758 (Serpentes, Colubridae): Data from the South Western Poland

Sexual dimorphism is widespread in animals, including snakes, and has impor- tant implication in both ecology and behaviour. I studied a grass snake (Natrix natrix) population from "Stawy Milickie" nature reserve. Mean snout-vent length (SVL) for fe- males was significantly greater than SVL for males, but males had proportionally longer tails. However, relative tail length (TL) in males decreased with increasing SVL whereas in females it was constant. Larger tails in males have frequently been associated with in- creasing mating success (e.g. tail wrestling behaviour between males). However, it is pos- sible this is less important in the population that I studied; instead, male snakes can allocate more energy to body growth.