Brood survival in the Red-backed Shrike Lanius collurio in eastern Poland

Abstract

Brood survival as an expression of breeding success is a component of bird fitness and the principal parameter underlying bird population dynamics. The main factor limiting brood survival is predation pressure, and birds have developed anti-predator strategies by selecting safer places for building nests and breeding. Here, we examined whether nest location affected the level of predation pressure. To do so, we analyzed brood survival in a Red-backed Shrike (RBS) Lanius collurio population breeding in the low-intensive agricultural landscape of eastern Poland. The mean survival probability for the whole nesting period was 0.540 and was higher for the incubation period (0.787) than for the nestling period (0.696). Cox’s proportional hazard model did not show any significant traits describing the location of the nesting shrub or the nest’s position in the shrub that could have affected RBS brood survival. We consider the composition of the local predator community to influence brood survival more than the location of a nest in the bush. The Eurasian Magpie Pica pica is mainly responsible for RBS brood predation. Red-backed Shrikes do not defend their broods against Magpies using acoustic signals and direct contact. Since Magpies search the bushes thoroughly, the shrikes’ nest concealment strategies are ineffective in the face of this predator.