Cost of Reproduction and Female Life-History Tactics in a Population of Grass Snakes, Natrix natrix, in Southern Sweden

Annual mortality rates were lower in immature than in mature grass snakes. The difference in mortality is suggested to be due to behavioural changes associated with reproduction. A simple model is presented suggesting that the increase in fecundity with increasing body size and the difference in mortality between immature and mature females are the main factors causing the delay in maturation in females as compared with male grass snakes.