Predictive cues and fitness consequences of breeding phenology

Individual variation in the timing of breeding in birds has been strongly linked to the fecundity, and by extension fitness of the individual. Despite this important relationship, our understanding of the determinants of timing of breeding is unclear. Photoperiod determines a window of opportunity for breeding, but small-scale variation within this window still has major fitness consequences. This thesis explores potential cues that might account for variation in individual timing decisions, and possible consequences of timing on offspring and future broods. First we assess how pre-breeding male social cues and the development of tipulid larva (prey) might determine the female’s timing of egg-laying. While many lab studies have demonstrated that the presence of a male partner is necessary for female gonadal development, our 3-year field studies found no effect of male behaviour on female breeding phenology or performance. This suggests that male song may not be an important supplemental timing cue. Next we explore potential consequences of timing on chick quality and multiple brooding behaviour. We demonstrate that somatic and physiological traits are more developed in chicks from earlier nests (first broods). We also document that physiological maturity, in the form of hemoglobin concentration, is related to fledgling flight ability. Although we show that second brood chicks maintain the same trajectory of development just prior to fledging, they may pay a higher cost in the form of oxidative stress. Finally we document that multiple brooding behaviour is unrelated to timing in our highly synchronous population, and instead relates to individual quality. Comprehensively, this thesis suggests that male social cues may not be important cues determining timing of breeding, and that the consequences of timing on offspring include maturity at fledging and oxidative stress, but not multiple brooding in our system.