In reptiles, the hatching and emergence of a single clutch may be synchronized or may take place over a number of days, weeks, or even months, depending primarily on the microenvironment of the nest. The present study focused on the patterns of hatching and emergence of Podocnemis unifilis hatchlings in an area of várzea floodplain on the lower Amazon River in Santarém, in the Brazilian state of Pará, in 2007 and 2009. Two groups of nests were monitored for hatching and emergence, with the nests in one group being undisturbed during the entire study period. The difference between the oviposition–hatching and oviposition–emergence intervals was determined based on the monitoring of these processes in the monitored clutches. Hatchlings took 1.5 d to leave the eggshell and the eggs at the top of the nest hatched first. The size of the clutch influenced the length of the interval between the first and last hatching. Most hatchlings emerged from a nest during a single night. Hatchlings in late nests and those closer to vegetation took significantly longer to emerge. The hatching–emergence interval was greater in 2007 (11.0 d) than in 2009 (7.3 d). This study contributes to the understanding of hatching and emergence patterns in P. unifilis and the physical and environmental factors that influence them, including the variation between reproductive seasons.

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