In turtles, the characteristics of the nesting environment have a strong influence on the
incubation temperature of eggs and, consequently, on the reproductive success. The effects of
the enviroment of nesting on the hatching rate, the duration of incubation and the sexual
determination of the nestlings of Podocnemis expansa, Podocnemis unifilis and Podocnemis
sextuberculata in the Embaubal nesting beach, Xingu River, Pará State, Brazil, in 2007, 2008
and 2010 were investigated. Nesting beaches were continuously visited between September
and January, in order to monitoring nests marked in the first day after oviposition, in each
reproductive season. The following features measured: day of spawning, depth to the first
egg, The nest’s height in relation to the river level, granulometry and temperatures of
inubation. The hatching rate differed between years for the three species. The duration f
incubation varied only between years P. sextuberculata. The sex ratio of P. expansa in 2007
was 0.08 and in 2008 and 2010 all the nestlings were females. In P. sextuberculata sex ratio
in 2007 was 0.34, and in 2008 and 2010 was 0.06. The sex ratio of P. unifilis in 2007 was
0.41, 0.65 in 2008 and 0.02 in 2010. All of these differences were significants statistically.
The nest’s height in relation to the river level presented positive correlation with the hatching
rate of the three species in 2008 and a negative relation with the hatching rate of P.
sextuberculata in 2010. The number of days after the beginning of the spawnings influenced
the duration of incubation of P. sextuberculata and P. unifilis in 2008. The average
temperature, the number of hours/degree above of 32°C and the size of the sediment
influenced the sex ratio of P. expansa. The results attest to the variation in hatching success,
embryo development and sex ratio produced between years. Still, it was observed that the
influence of microclimatic variables of the selected sites for nesting in nesting success and sex
ratio varied between years, which is a clear evidence that climatic conditions plays a major
role and causes changes in the parameters examined thorough a nesting season and between
nesting seasons in subsequent years. It is recommended the continued monitoring of the
related parameters in the main areas which is invest the protection the reproductive sites of
turtles.
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