REGULATION OF MULTIANNUAL VOLE CYCLES BY DENSITY-DEPENDENT AVIAN AND MAMMALIAN PREDATION

A mortality factor should be density-dependent to regulate population density. In western Finland, vole (Microtus spp.) populations fluctuated in 3-4-yr cycles in a farmland area. During 1977-87, the mortality rate of voles by breeding avian predators was positively correlated with vole density in spring. Accordingly, vole mortality by avian predators directly depended on prey density, and avian predators have thus a potential to reduce the amplitude of the multiannual vole cycle. Vole kill rates of least weasels during six winters were significantly positively related to the prey densities in the preceding spring (3/4-vr lag). The same relationship for the stoat was als positive but not significant. In seasonal environments, 3-4-yr vole cycles might be driven by a density-dependent mechanism affecting the growth rate of vole populations with a 9-month lag (May 1981). My results suggest that one mechanism producing this critical lag could be mustelid, especially least weasel, predation.