Effect of Prey Density on Reproduction, Foraging and Other Activities in the Adder, Vipera berus

Abstract

AbstractReproduction, foraging and other activities of an island population of adder, Vipera berus, were documented in 1974 after a high density of rodents in 1973. The study was repeated in 1975 after one year of diminished food resources. In spring 1974 the weight status (body mass/length) of all categories of island adders was significantly higher than in adjacent mainland populations. After one year of food scarcity mean body mass had decreased significantly in all categories of adders. At the same time mean body length in males, (but not in females) increased significantly. Survival after one year of low food resources was markedly higher in non-reproductive females than in reproductive ones, pointing to a high cost of reproduction at low food density. In 1975, spring sloughing in males was delayed and prolonged, and reproduction failed completely. The foraging period was prolonged and included spring. Most adders then left their normal spring habitats close to the hibernation area and moved to foraging habitats. Predator evasion distance was much shorter than in well-nourished adders.