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

1. We tested experimentally the e€ects of exposure to high ambient temperatures, for periods of 1±9 days, on the viability of eggs of the green-rumped parrotlet. 2. The hatchability of 534 newly laid parrotlet eggs declined after exposure of 3 or more days. 3. The probability of hatching was not signi®cantly a€ected by the duration or proportion of time exposed to temperatures below physiological zero or above normal incubation range. 4. Incubation periods were negatively correlated with exposure time, suggesting some embryo development occurred prior to incubation. 5. Results presented here corroborate similar studies of temperate zone birds, and suggest that the decline in egg viability may be particularly extreme in hot climates, such as tropical lowlands. 6. We suggest that the relationship between ambient temperature and egg viability could contribute to both seasonal and latitudinal trends in clutch size, hatching success and hatching asynchrony.