The relative importance of brood reduction, predation and parental investment in the evolution of hatching asynchrony in yellow warblers (Dendroica petechia)

Fledging mass and survival rates of first-hatched chicks were generally higher in asynchronous broods, and nestling mortality in asynchronous broods was concentrated in last-hatched nestlings. In synchronous broods, on the other hand, nestling mortality was random with respect to hatching order. The trend for fledging success to be higher in asynchronously hatched broods, especially when food was apparently limiting was also apparent. Fledging mass and survival rates were similar for last-hatched chicks in asynchronous and synchronous broods.;Feeding rates over the entire nestling period were generally similar for females tending asynchronous and synchronous broods of 4 or 5 nestlings. Male feeding rates over the entire nestling period were lower in asynchronous broods, and significantly so in broods of 5, compared to males tending synchronous broods. There appears to be no conflict between the sexes as to when incubation should begin.;Observations showed that full incubation was delayed until the last egg was laid or later. The data also showed that incubation attentiveness is increased experimentally by adding eggs during early egg laying. These results suggest that initiation of full incubation is not rigidly controlled by hormonal changes associated with the laying of the penultimate egg.;There were no differences between clutch sizes in the mass of last-laid eggs relative to the mass of their clutch-mates. The mass of the last egg also was not correlated with hatch spreads, or date of clutch initiation. (Abstract shortened by UMI.).;Daily survival probabilities (DSP) of nests, throughout the nesting cycle, were used to calculate expected productivity ratios. The DSP of nests increased significantly from laying to fledging. As a result, expected productivity ratios were greatest when incubation began with the laying of the first egg. However, observed hatching spreads indicated that female Yellow Warblers delayed incubation at least until the laying of the ante-penultimate egg. This suggests that the probability of total nest failure due to predation has likely not played an important role in the evolution of hatching asynchrony in Yellow Warblers.