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)

We analysed sexual dimorphism, various aspects of feeding ecology, and reproductive traits of the grass snake (Natrix natrix) population inhabiting the marshy-swamp ecosystem of Bardača. Through a capture-mark-recapture study, between 2011 and 2014, the first long-term investigations of this snake species were commenced in Bosnia and Herzegovina. A total of 172 adult individuals (96 ♀ : 76 ♂) have been captured and marked. Females reached larger overall body dimensions than males (maximum snout-vent length, SVL, was 994 mm and 640 mm, respectively) and had longer jaws than males of the same body length. On the other hand, tails were relatively longer in males compared to females (22.3% and 19.3% of total body length). Diet analysis revealed yearly differences in qualitative composition of prey, which confirmed intra-population plasticity in the grass snake’s diet. We also found differences in the direction of prey swallowing depending on the prey type (frog or fish): anurans were significantly more often swallowed tail-first, and fish head-first. Also, we found intersexual differences in prey type: females consumed more diverse prey and ate green frogs (Pelophylax sp.) significantly more often. Females reach adulthood at SVL of 62.6 cm and males at SVL of 48.5 cm. Clutch sizes ranged between eight and 28 eggs, and the correlation between female body size and clutch size was positive.