Abstract:
Climate change threatens species with temperature-dependent sex determination as further
warming could result in extremely biased sex ratios or offspring of only one sex. Among
the possible adaptations of sea turtles to climate change, are behavioral responses toward
nesting in cooler areas. We analyzed nesting patterns of East Pacific green turtles (Chelo-
nia mydas) in Costa Rica to determine the occurrence of nest-site selection and how this
could influence primary sex ratios (PSR). Green turtles exhibited nest-site repeatability.
Nests placed by the same individual were generally closer (mean distance: 237.4 m) than
other nests on the beach (mean distance: 411.0 m) and this repeatability was maintained
in different nesting seasons. Additionally, turtles tended to place late nests closer to each
other than their early nests, suggesting an adjusting nesting behavior throughout the nest-
ing season. A great majority of nests were placed in the vegetation (80.9%) and within this
zone, turtles preferred nesting under trees (78%) than in grass areas (28%), where tem-
peratures were cooler and PSR were less female biased. Mean nest temperature (°C) during
the thermosensitive period and mean PSR were 30.7 ± 1.2 °C and 79 ± 4%, respectively.
Most years were female-biased or extremely female-biased but there was approximately
one male-biased year in the decade. Although many nests produced 100% females, some
male hatchlings were produced every year, even during the extreme 2015–2016 El Niño
event. The preference of green turtles for nesting in shaded areas could help to mitigate
the negative impacts of climate change unless temperatures in shaded areas rose above the
male producing temperatures.
