Sexual dimorphism, feeding ecology, and reproductive traits in the grass snake (Natrix natrix) from the Ramsar site “Bardača Wetland” (Republic of Srpska, Bosnia and Herzegovina)

Through a capture-mark-recapture study, between 2011 and 2014, the first long-term investigations of the grass snake (Natrix natrix) were commenced in Bosnia and Herzegovina. A hundred-and-seventy-two adult individuals (96 ♀ : 76 ♂) have been captured and processed. Females reached larger overall body dimensions than males and had longer jaws than males of the same body length. On the other hand, tails were relatively longer in males compared to females. These results illustrate the typical sexual dimorphism in this species. Diet analysis revealed natural yearly variation in the qualitative composition of prey, which confirmed intra-population plasticity in the grass snake’s diet. Also, their diet was strongly influenced by the drying of ponds. We found differences in the direction of prey swallowing depending on the prey type (frog or fish), which was conditioned by prey morphology. We also found intersexual differences in prey type: females consumed more diverse prey and ate green frogs (Pelophylax sp.) significantly more often. This finding results from sexual differences in head dimensions and illustrates differences in the energetic contents of different prey types. Clutch sizes ranged between eight and 28 eggs, and the correlation between female body size and clutch size was positive. These results are within the ranges of previously published findings. Semi-aquatic snakes are important elements of wetland ecosystems, and can indicate their condition. Long-term population studies of these animals can provide warning signals of wetland ecosystem disturbance and the need for immediate conservation actions.