Timing of egg-laying in relation to a female’s social environment in European starlings

Abstract

It is widely assumed that female birds use non-photic supplemental cues, including social factors, to fine-tune timing of egg-laying to local conditions, but our knowledge of the nature of these social cues and how they operate remains limited. We analyzed the relationship between a female’s social environment (nearest neighbor distances, residency, female -and- network familiarity, synchrony) and variation in timing of egg-laying in European starlings (Sturnus vulgaris) using individual, residual laying date (controlling for annual variation) and temperature-independent residual laying date (accounting for the effect of ambient temperature on laying date). Female social environment varied systematically with overall spatial distribution of nest-boxes (linear vs clumped boxes) but this was not associated with spatial variation in laying date or temperature-independent residual laying date. We found no evidence for any relationships between individual variation in social environment and individual, residual laying date and only weak evidence for any association with individual, temperature-independent residual laying date. The latter was associated with a) nearest neighbor distances in the linear habitat, with females nesting closer to neighbors laying earlier than predicted by temperature, but not in the two clumped habitats, and b) neighbor familiarity: females with an intermediate number of returning females (3/8) laid closest to the predicted date. Finally, despite the fact that synchrony was not associated with other social environment metrics, females with lower laying synchrony among neighbors laid earlier than predicted by temperature. This suggests that some components of the female-female social environment could act as supplemental cues for timing of egg-laying.