Ural owl predation on field voles and bank voles by size, sex and reproductive state

摘要

Predation on selected individuals from a population may have consequences for the prey population. We studied predation of breeding Ural owls (Strix uralensis) in southern Finland on their two main prey species, field voles (Microtus agrestis) and bank voles (Myodes glareolus)which fluctuate in abundance between years. We identified sex, body mass and reproductive state of the voles in Ural owl nests and of voles caught by snap-trapping in the study area. Our results showed that Ural owls preyed proportionally more upon reproductively active field voles than expected, whereas no such bias was found for predation on bank voles. There was no difference in sex ratio between preyed upon and trapped field voles or bank voles. Ural owls captured heavier individuals of both field voles and bank voles than expected, and in field voles, but not bank voles, reproductively active individuals were heavier than reproductively inactive individuals. We discuss how differences in social organisation, dispersal and reproductive behaviour may differently affect predation vulnerability of field voles and bank voles. In contrast to the pattern documented in other owl species, we find that Ural owls select larger and reproductively active voles, and may thereby exert a higher population-dynamical impact on vole populations than expected solely from the numbers of voles preyed upon.