Egg viability as a constraint on hatching synchrony at high ambient temperatures

1. We tested experimentally the effects of exposure to high ambient tempera tures, for periods of 1-9 days, on the viability of eggs of the green-rumpe d parrotlet. 2. The hatchability of 534 newly laid parrotlet eggs declined after exposur e of 3 or more days. 3. The probability of hatching was not significantly affected by the durati on or proportion of time exposed to temperatures below physiological zero o r above normal incubation range. 4. Incubation periods were negatively correlated with exposure time, sugges ting some embryo development occurred prior to incubation. 5. Results presented here corroborate similar studies of temperate zone bir ds, and suggest that the decline in egg viability may be particularly extre me in hot climates, such as tropical lowlands. 6. We suggest that the relationship between ambient temperature and egg via bility could contribute to both seasonal and latitudinal trends in clutch s ize, hatching success and hatching asynchrony.