Timing of Breeding Determines Growth and Development in a Long-Distance Migratory Bird

The timing of breeding can have significant consequences for adult and offspring fitness, yet our current hypotheses of seasonal timing focus on the parent perspective. When offspring survival is affected by timing of breeding, we expect to see offspring mechanisms to detect and respond to cues of seasonal timing. Avian embryos respond to photoperiod and seasonal cues during development and in this study we evaluate the influence of photoperiod and season on posthatching growth and development in Franklin's gull (Leucophaeus pipixcan). Early- and late-season chicks exposed to short and long photoperiods during development were reared under common garden conditions. Photoperiod had no effect on posthatching growth and development, but seasonal effects present in the egg (maternal egg effects or genetic) did influence posthatching growth and development. Late-season chicks grew body mass and primary flight feathers at faster rates than early-season chicks, which we hypothesize facilitates independence and readiness for migration. Growth rates are complex phenotypes and we propose a general growth model that incorporates delays in negative feedback systems regulating growth. We show that the timing of breeding programs intrinsic growth rates in offspring, which suggests that many of the metrics used to describe seasonal patterns of reproductive success may be biased.