Wintering the common viper (Vipera berus) with embryos

For the Vipers from Karelia phenomenon wintering females with embryos and the annual breeding were found. They were very large and heavy females (L.t. > 62 cm, W > 160 g), for which the mass loss due to pregnancy are not significant. Analysis of the size of 1450 individuals in a Kizhi population of viper showed that the proportion of females that can hibernate from embryos amounts to less than 3%.