Habitat choice by melanistic and cryptically coloured morphs of the adder, Vipera berus

Melanistic adders (Vipera berus) have been considered to be ecologically superior to cryptic ones in cold climates because of their higher thermoregulatory efficiency. However, a popular hypothesis states that black snakes should be more exposed than cryptic ones to visually oriented 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 melanistic morph (ESS model). Moreover, because of this higher risk of predation, it has been suggested that black adders should essentially inhabit forested zones, where they can escape from visually oriented predation. To test this hypothesis, we performed a field study on habitat choice by a polymorphic population of adders. Our data showed that habitat choice by adders strongly depended on seasonally, but not on colour pattern. Adders almost always selected open habitat in spring (during the mating period), and a variety of habitats (including forested zones) in summer, in relation to their individual feeding and reproductive status. However, in any season there were significant differences between the habitat selection of cryptic and melanistic adders.