Weasels Mustela Nivalis Suppress Reproduction in Cyclic Bank Voles Clethrionomys Glareolus

Abstract

The bank vole Clethrionomys glareolus (Schreber), was studied in enclosures and on islands in Central Finland in 1982-88. Winter breeding was observed in 1983-84 and 1986-87, both of which were years of increasing microtine populations. No mustelids were observed in the study areas during these winters. Local microtine populations peaked in 1987-88. However, when bank voles were kept in large enclosures at fairly low densities during winter, female voles were found to have perforated vaginae and males scrotal testes by February 1988. The first litters were born as late as two and a half months later. This delay between maturation and parturition could have been due to the presence in the study area of one or more weasels Mustela nivalis L. between January and March. This idea was tested in a laboratory experiment: the presence of a weasel close to the breeding pairs of bank voles suppressed the reproduction in all four cases. In the control group, without a weasel successful fertilization occurred in three females out of four. The observations indicate the importance of indirect effects that the presence of specialist predators have on the breeding behaviour of their prey.