Meeting Abstract
Temperate-zone vertebrates use initial and local predictive cues to time reproduction to optimal breeding conditions, yet individual variation in timing of reproductive output (i.e. clutch initiation) is observed. Numerous laboratory studies have revealed that light experienced during a critical window of the circadian period is capable of influencing reproductive physiology. Interestingly, laboratory studies have also revealed significant individual variation in endogenous circadian rhythms. However, whether this individual variation in endogenous daily rhythms influences variation in seasonal responses to light remains largely unexplored in the wild. Here we test the hypothesis that individual variation in endogenous timing phenotypes recorded in nature (i.e. chronotype) are linked with variation in seasonal timing of breeding. To address this hypothesis we utilized incubation behavior data to identify individual patterns of awakening time in two temperate-breeding songbird species, the Great Tit (Parus major) and the Dark-eyed Junco (Junco hyemalis). We found individual awakening time to be repeatable in both species, justifying it as a consistent, measurable phenotype. Importantly, we found that females who departed from their nest earlier in the day also initiated nests earlier in the year in both species. Date of data collection and ambient temperature did not affect awakening time. Our findings suggest a role for endogenous behavioral rhythms as one mechanism underlying the observed variation in seasonal timing of breeding.
