Variation in the onset of incubation in a neotropical parrot

We studied the onset of incubation in the Green-rumped Parrotlet (Forpus pa sserinus), a cavity-nesting species with female-only incubation starting on the first egg and asynchronous hatching. We quantified how the onset of in cubation varied among individual females, with stage of egg-laying and by u ltimate clutch size. We then examined whether this variation affected the i ncubation period and hatching success of individual eggs. Female parrotlets initiated incubation in three characteristic patterns: slowly rising, rapi dly rising, and pulsed. The diurnal incubation rate of the first egg was 80 .0% and increased as the laying cycle progressed, but was not affected by u ltimate clutch size. Females that were fed more often by their mates during laying had lower incubation rates. First-laid eggs had longer incubation p eriods than later-laid eggs, but nearly all eggs hatched in the order they were laid. Hatching success was not affected by laying order. Despite the s trong hatching asynchrony and consistent first-egg incubation exhibited by this species, we found significant variation in the onset of incubation, al though no serious fitness consequences of this variation were detected.