Use of artificial refuges by the northern viper Vipera berus -3. An experimental improvement to the thermal properties of refuges

摘要

To increase the use of galvanised corrugated-iron refuges ('tins') by northern vipers (Vipera berus) in a chalk downland reserve, insulation mats were placed on half of the bare ground area below the tins. During the day time the operative temperatures (T_e) on the mats, demonstrated by physical models, averaged 2-4℃ warmer than bare ground under the same refuges but ranged as much as 10℃ warmer. Vipers were found more frequently under insulated than uninsulated tins and, when under these tins, were more likely to be on the mat than on the bare ground. Adult males on mats in March/early April had body temperatures (T_b) 9.4°-15.8℃ higher than Te (which at this time of year is particularly low). At other times adult males, females and juveniles were on average about 1 to 2℃ warmer but, surprisingly, subadults showed no temperature difference. Insulation mats, by enabling the vipers to maintain higher Tb, should improve their physiological performance and if they reduce open basking and the incentive to search for warmer positions then they could reduce exposure to avian predators. The inclusion of an insulation mat as a component of an improved refuge design is now under investigation.