The importance of rainfall

Sea turtles lay their eggs in underground nests on sandy beaches. The eggs are then left to incubate unattended and are subject to a suite of environmental conditions. The interplay of these environmental variables affects important factors such as the development rate and hatch success of the nest.

Since sea turtles exhibit temperature-dependent sex determination, the incubation temperature of the egg also determines the sex of the offspring. Warm incubation temperatures (typically above 29 °C) lead to a majority of females being born whereas cooler temperatures lead to males being born.

A new study published recently in Endangered Species Research shows the importance of rainfall throughout the incubation process. The researchers from Florida Atlantic University (USA) recorded rainfall and sand temperatures at a loggerhead turtle nesting beach in Florida. Ms Lolavar, the lead author of the study, tells me that the results of the study show that “heavy rainfall events can cool the sand and bring the incubation temperature of a nest in the male-producing range. However, if beach temperatures are too warm, which is often the case in Florida, most rainfall events don’t shift the nest temperature enough to produce males.”

This is not a phenomenon limited to Florida of course. A 2007 study of leatherbacks nesting in Grenada showed similar results. What sets the new research apart is that the Florida researchers also determined the sex of hatchling sea turtles laparoscopically. This enabled them to empirically show that during particularly rainy nesting seasons more male turtles hatched.

Ultimately, this study shows that understanding the effect of rainfall on incubation temperatures is key to anticipating the effects of the changing climate on sex ratios, and thus for the successful long-term conservation of sea turtles.

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Loggerhead hatchlings: are they female or male?