One every thousand nests !

Photo by A. Sanz-Aguilar

We have probably measured eggs and the clutch size of more than one thousand nests since 2007, when we began monitoring  the Yellow legged gulls at the Natural Park of Sa Dragonera. This year, for the first time we found a nest with 5 eggs. Most likely a case of egg dumping. 

Happy easter!

New publication on marine Turtles!

Heredero Saura, L., Jáñez-Escalada, L., López Navas, J., Cordero, K. and Santidrian Tomillo, P. 2022 Nest-site selection influences offspring sex ratio in green turtles, a species with temperature-dependent sex determination. Climatic Change 170, 39 (2022). DOI: 10.1007/s10584-022-03325-y

 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 (Chelonia 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. 

Photo from www.fisheries.noaa.gov

Additionally, turtles tended to place late nests closer to each other than their early nests, suggesting an adjusting nesting behavior throughout the nesting 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 temperatures 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.

 Press releases in Spanish here and here