Variation in the onset of incubation and its influence on avian hatching success and asynchrony

Variation among species in the onset of incubation has been attributed to differences in life history traits, and variation within species has been related to individual and environmental factors. We quantified within- and among-species variation in the onset of incubation in five cavity-nesting passerines, using a continuous record of diurnal and nocturnal incubation from clutch initiation through completion. We documented 11 potential patterns for the onset of incubation and showed that onset patterns were significantly related to hatching success. The onset of diurnal partial incubation and nocturnal full incubation generally occurred before diurnal full incubation, which started around clutch completion. Increases in precipitation or wind speed significantly delayed most types of incubation onset, supporting predictions of the energy constraints hypothesis. Ancillary predictions of rain and wind disproportionately delaying incubation for aerial foragers, and for species with male feeding during incubation, were not upheld. Larger clutch size accelerated the timing of full incubation onset in diurnal and nocturnal full incubation, supporting predictions of the egg viability hypothesis. Predictions of both hypotheses for the effects of minimum temperature, proportion of time above 24 °C, and seasonality on incubation onset were not supported. We observed egg neglect for up to 4 days or nights; neglect was more common at night, and consecutive nights of neglect occurred during nocturnal full incubation. Egg neglect did not significantly affect hatching success or incubation period. In conclusion, the timing of incubation onset was strongly affected by environmental and individual factors, and patterns of incubation onset affected hatching success.