Vole-induced regular fluctuations in the Estonian owl populations

Estonia has been considered to hold non-cyclic vole populations, which shou ld be revealed in owl productivity or movements. I asked (1) whether owl an d vole populations fluctuate regularly in Estonia, (2) are the fluctuations in Estonia synchronous to those in its neighbouring areas, (3) do Estonian and northern owl populations exchange individuals? I found significant per iodicity in owl reproduction, which was linked to vole abundance, suggestin g that Estonia belongs to the transition zone between cyclic and non-cyclic vole populations. The migration intensities of nomadic owl species were po sitively correlated with each other, and in the long-eared owl related to i ts productivity. Having found that owl productivity fluctuates independentl y in Estonia and southern Finland, and owls do not move freely between the countries, I discussed possible causes for this.