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Influence of geological factors on reproductive aspects of Podocnemis unifilis (Testudines, Pelomedusidae) on the Javaes River, Araguaia National Park, Brazil


, : Influence of geological factors on reproductive aspects of Podocnemis unifilis (Testudines, Pelomedusidae) on the Javaes River, Araguaia National Park, Brazil. Chelonian Conservation and Biology 4(3): 626-634

Podocnemis unifilis nests in extensive sandbanks on the margins of the Javaes River in Araguaia National Park, Tocantins State, Brazil. These sandbanks are made up of sedimentary deposits of diverse constituents which combine in a complex textural and granulometric arrangement. In morphological terms, the sandbanks, which are referred to as beaches, can be divided into two categories of nesting sites: shoals and flat areas near the river channel, and areas in front of sand dunes. The turtles nest in shallow pits 12[long dash]25 cm deep, and their eggs are subject to intense predation by birds and reptiles. In the 1999 season, all turtle nests deposited in the shoals and flat areas adjacent to the river were depredated. The only nests not depredated were those located at the foot of sand dunes, where, due to wind action, the beach sediments are continuously re-worked and deposited along the front portion of the dunes on top of the nests. The piling up of sediments on these nests was, on average, over 10 cm, with additional depths of up to 36 cm being recorded, providing extra protection for the eggs and allowing successful incubation.

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