Life-history and diet of two populations of Natrix maura (Reptilia, Colubridae) from contrasted habitats in Sardinia

Aspects of general ecology and population biology of two populations of freeliving viperine snakes (Natrix maura) were studied in Mediterranean localities of the island of Sardinia (Thyrrenian Sea, Italy). The apparent adult sex-ratio was not significantly different from equality, but males were slightly more numerous than females. The diet consisted mainly of arnphibians, both adults and tadpoles (area A) or fish (area B). Females were significantly longer than males. Reproduction was yearly, and clutch size and female total length were positively correlated. A hundred and seven live offsprings were obtained from 135 eggs (79.2% of successful incubation rates). The proportion of unsuccessful incubation was not significantly correlated with either female total length or clutch size. There was no evidence of a trade-off between clutch size and offspring size, as hatchlings were no smaller in clutches that were unusually large in relation to maternal body size. Oviposition date was correlated with neither maternal length nor clutch size. lncubation period was significantly correlated with mean hatchling size, but not with either clutch size or maternal length. No female died after oviposition, thus suggesting a very low incidence of mortality rates dueto starvation and reproductive costs. A case of long-term sperm storage deriving from autumnal mating is described. Population size estimates are provided for both study areas. Key words: Natrix maura, Ecology, Mediterranean region, Sardinia.