Brain size mediates the choice of breeding strategy in the Red-backed shrike Lanius collurio

Abstract

Brain size of vertebrates is a trade-off between natural selection for enhanced cognitive abilities and the energetic constraints of producing brain tissue. Processing a large amount of information can be beneficial but is also time-consuming. Breeding strategy choice, whether it comes to timing of breeding onset or nest-site selection, can be related to the size of the brain. Our study aims to reveal if there is relationship between brain size, timing of breeding, nest-site choice, and breeding success in Red-backed shrike Lanius collurio. We found that first egg laying date was affected by females' head size, with large-headed females laying eggs later in the breeding season. The study also found that the probability of breeding success increased with increased nest concealment, however, the relationship was negligible in large-headed males. In turn, the nest concealment was not affected by head size but only by the date of the breeding onset. The study suggests that the choice of breeding strategy may be mediated by brain size: large-headed females may take more time to choose a nesting site, which may delay the onset of breeding, and large-headed males may be able to compensate for poor nest concealment.