Individual variation in foraging effort of breeding birds

Parental care (e.g. provisioning nestlings) is widely assumed to be costly, and life-history theory predicts a trade-off between reproduction and future fecundity and/or survival. However, experimental studies manipulating workload during parental care and demonstrating fitness effects are either rare or have mixed results. Here, we took a two-step approach to this problem in European starlings (Sturnus vulgaris): 1) using a 4-year dataset to ask if changes in parental investment in handicapped (wing-clipped) parents, and the fitness consequences of these decisions, vary among years (i.e. with ecological context), and 2) using an automated radio telemetry system to determine if females alter their activity to compensate for an increase in workload. We found marked individual and annual variation in response to the handicapping treatment. In addition, clipped individuals dramatically reduced their activity, while sustaining current breeding productivity, suggesting that clipped individuals reduce self-maintenance to favour their current reproductive bout.