Cold Resistance and Wintering of the Common Viper (Vipera berus, Reptilia, Viperidae) on Kizhi Island, Karelia

Abstract

Abstract: The geographic distribution of the common viper, Vipera berus (L. 1758), was believed to be limited in the north and northeast by an assumed lack of hibernacula with temperatures exceeding 0°C, because the species is not freeze-tolerant. To test this hypothesis, we measured in the laboratory the cold resistance of vipers that inhabit Kizhi Island (Lake Onega, Karelia, Russian North), and compared the results obtained with the temperatures in the hibernacula and soils of the region. Freezing of the adults happened at an average temperature of −3.0°C (ranging from −2 to −3.9°C). Vipera berus failed to tolerate complete freezing, but could withstand short-term (1–8 hours) partial freezing. At subzero temperatures (−2 to −2.2°C), animals remained supercooled for 23–121 days. Vipers remained active at temperatures dropping down to −1.5°C, moving in experimental containers; this possibly happens in overwintering places as well. Our study allows us to conclude that the species’ ability to withstand long-term supercooling (up to four months) is one of the key determinants of the adaptive strategy of the common viper in cold regions. The critical temperature of the species in overwintering sites must be considered to be not 0°C, but −2°C. This threshold temperature can be a factor limiting the geographic distribution of V. berus. Temperatures in hibernacules on Kizhi Island (heapes of stones) and also possibly in all soils of Karelia are favorable for the species’ overwintering, leading to its great abundance levels.