SPATIAL-DISTRIBUTION OF GREEN TURTLE (CHELONIA-MYDAS) NESTS AT TORTUGUERO, COSTA-RICA

We monitored spatial distribution of nests of green turtles, Chelonia mydas, for three years at Tortuguero, Costa Rica. The beach was divided into three zones from water's edge to supralittoral vegetation depending on the extent of vegetation cover. The extent of shade affects the temperature of the nest and, ultimately, the sex of the offspring in that nest through environmental sex determination. Patterns of nest distribution among beach zones within and among years were evaluated both for the population and for individual turtles. Distribution of nests among the three zones varied among years. Individual turtles that nested three or more times within a season more often deposited clutches in more than one zone than in just one zone. Individual green turtles are more likely to conform to the population's pattern of nest distribution each year than to maintain their own individual pattern between years. Thus, annual factors apparently have a greater effect on nest placement than do individual nesting patterns. The lack of any consistent pattern of nest distribution may result from environmental uncertainty and low predictability of nest success. Because patterns of nest placement are not consistent either for the population or for individuals, we predict that primary sex ratios will vary from year to year for both the Tortuguero population and for the offspring of individual turtles. The distribution of nests of hawkbills, Eretmochelys imbricata, at Tortuguero within each year is not different from that of the green turtle.