ANNUAL VARIATION IN GROWTH-RATE AND BODY CONDITION OF ADDERS, VIPERA-BERUS - EFFECTS OF FOOD AVAILABILITY AND WEATHER

The objective of this study was to see if year-to-year variation in si ze-specific growth rate and body condition of adders, Vipera berus, wa s correlated with any of four environmental variables: mean summer tem perature, number of sunny days during summer, number of days when the temperature was over 15 degrees C during summer, and vole density as a n index of food abundance. Growth rate and body condition were measure d during 5 years in two insular populations of adders (at localities A and I) in central Sweden. At locality A, vole density remained consta nt among years (range 0.86-3.00/ha), whereas at locality I it changed significantly (0.67-22.67/ha). The two localities were approximately 2 km apart and therefore experienced the same weather conditions. At Id eality A, growth rates (after sex and snout-vent length were controlle d for) remained stable, whereas at locality I they varied significantl y among years and showed a significant positive correlation with yearl y estimates of vole density. I conclude that the growth rate was affec ted positively by food abundance, but less so by weather. Body conditi on of male adders (females were excluded because the sample size was s mall) varied significantly among years in both populations. At localit y A, body condition was positively correlated with number of sunny day s, whereas at locality I, where vole density changed over the years, b ody condition was positively correlated with both vole density and num ber of sunny days. This suggests that both food abundance and weather may be important in determining body condition.