THE EFFECT OF SILVER BIRCH (BETULA-PENDULA) POWDER ON PHYSIOLOGICAL PERFORMANCE OF FIELD VOLES (MICROTUS-AGRESTIS)

Many northern arvicoline rodents consume bark of woody plants in times of high population densities. However, the significance of this behav iour to voles themselves is poorly known. We fed adult field voles (Mi crotus agrestis) for two weeks on diets containing 15% to 20% protein mixed with birch (Betula pendula) twig powder in concentrations of 0%, 10% or 50% on dry weight basis. Addition of birch powder increased co nsumption, but did not affect significantly the body mass of voles. Wi th increasing amounts of birch powder the most pronounced effects were increased liver size and activation of two microsomal detoxication en zymes. The results confirm that birch twig is low quality food for the field vole. High proportion of woody forage in the diet may cause sev ere physiological stress and contribute to the sudden crashes of vole populations.