HABITAT CHOICE BY MELANISTIC AND CRYPTICALLY COLORED MORPHS OF THE ADDER, VIPERA-BERUS

Melanistic adders (Vipera berus) have been considered to be ecological ly superior to cryptic ones in cold climates because of their higher t hermoregulatory efficiency. However, a popular hypothesis states that black snakes should be more exposed than cryptic ones to visually orie nted predation, and that the frequency of both colour morphs within a given population is maintained by the equilibrium existing between the reproductive advantage and the higher risk of predation of the melani stic morph (ESS model). Moreover, because of this higher risk of preda tion, it has been suggested that black adders should essentially inhab it forested zones, where they can escape from visually oriented predat ion. To test this hypothesis, we performed a field study on habitat ch oice by a polymorphic population of adders. Our data showed that habit at choice by adders strongly depended on seasonality, but not on colou r pattern. Adders almost always selected open habitat in spring (durin g the mating period), and a variety of habitats (including forested zo nes) in summer, in relation to their individual feeding and reproducti ve status. However, in any season there were significant differences b etween the habitat selection of cryptic and melanistic adders.