Do breeding Ural owls Strix uralensis protect ground nests of birds?: an experiment using dummy nests

摘要

Predatory birds were formerly suggested to have only negative effects on the breeding success of other birds that breed in the vicinity of their nests. However, the predator may also protect these breeding birds by chasing away other nest predators whilst either defending its own nest or by eating other predators in its territory. Ural owl Strix uralensis is known to be an aggressive nest defender. Although its diet mainly consists of voles, it also preys upon bird species (e.g. Corvidae) and even weasels Mustela nivalis, particularly when the vole densities are low. We carried out a dummy nest experiment on six Ural owl territories in central Finland to study whether Ural owls affect the nest predation rates of ground nesting birds. We found that although dummy nest predation differed between Ural owl territories, in every territory the predation risk was lowest in close proximity to Ural owl nests. The protecting effect of the predator continued for a distance of up to several hundred metres from its nest; a much further distance than could be expected if the effect was due solely to the defence of its own nest. Consequently, as suggested for other predatory birds, it may be that breeding Ural owls influence the bird community both directly by predating upon some species and/or indirectly by providing protection for other species. However, natural evidence on breeding habitat selection and predation risk of ground nesting birds should be obtained before detailed inferences on the effects of Ural owl nests on bird community levels are made.