Warming-induced sex bias fuels deceptive conservation success in sea turtles

Abstract

Global warming threatens species with temperature-dependent sex determination (TSD) by risking extreme offspring sex-ratio bias. In sea turtles, warmer incubation conditions produce more females. Such biases can transiently inflate apparent population growth before male scarcity undermines reproduction, possibly leading to population extinction. Here, we combine 15 years of field monitoring, drone-based sex-ratio surveys, Argos telemetry, and eco-physiological modelling to test whether rising temperatures underpin the rapid increase in loggerhead (Caretta caretta) nesting in Cabo Verde, one of the worlds largest populations. Historical air temperature, lagged by one generation, predicts current nest counts, consistent with a climate-driven, female-biased population. Drone surveys reveal an approximately 9:1 female-to-male breeding sex ratio across two consecutive breeding seasons, and simulations reproduce observed nesting trajectories under historical warming but not under null (no-warming) scenarios. Extending the analysis to 28 global loggerhead populations reveals consistent links between temperatures, latitude, and nesting trends. Our results identify warming-induced sex ratio bias as a key, yet deceptive, driver of apparent recovery, highlighting the need to reassess conservation success through the lens of demography of TSD species.