Could fluctuating prey availability change protective nesting associations in forest birds? A hypothesis

Abstract

One of the most striking behavioural adaptations for reducing nest predation is nesting near a top predator. However, in spite of increasing number of studies in forested landscapes reporting reproductive success benefits when nesting near protective associates, studies examining whether protective effects vary with food availability for the top predator are lacking. We asked whether the nest predation on ground nests of birds in Ural Owl (Strix uralensis) territories is dependent on varying food conditions for the owl. This was studied using dummy nests placed at different distances from the Ural Owl nests and repeating the study in different food conditions for the owls (low, increase and peak phases of the vole cycle). The proportion of predated dummy nests differed between different food conditions for Ural Owls being lowest in a low vole year. The distance from the owl nest affected the predation of dummy nests, but only in intermediate food conditions. Due to the lack of control nests located outside the owl territories, we are not able to draw conclusions about the background variation in the nest predation in different food conditions. We hypothesise that fluctuating prey availability for the top predator species under concern may have significant effects on the outcome of species interactions. This currently unexplored idea should be tested further, e.g. by including multiple breeding seasons in the future studies on protective nesting associations.