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. Whether it comes to the timing of breeding onset or nest-site selection, the choice of breeding strategy can be related to the size of the brain. Our study aims to reveal whether there is a relationship between brain size, timing of breeding, nest-site choice, and breeding success in Red-backed shrike Lanius collurio. We found that the first egg laying date was affected by the size of the female 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 larger-headed males. In turn, nest concealment was affected not by head size but only by breeding onset. The study suggests that the choice of breeding strategy may be mediated by brain size depending on sex: large-headed females may take more time to choose a nesting site, which may delay the onset of breeding, and large-headed males may benefit from, or at least be able to compensate for poor nest concealment.