Over 90% Of Turtles Born Female Due To Global Warming

Climate change is affecting wildlife in a lot of serious, and occasionally weird, ways. It’s destroying the icy habitats of polar bears and walruses.

Now, scientists have revealed another unexpected climate effect: It may be disrupting the sex ratio among baby sea turtles.

In a new paper published last week in the journal Endangered Species Research, researchers explored how changes in rainfall and temperature could affect the sex of baby loggerhead sea turtles, and found that, in southeast Florida at least, climatic changes seem to be producing more female babies.

Loggerheads, like other species of sea turtles, develop into males or females while they’re still incubating in their eggs depending on a variety of environmental influences.

Temperature is one of the most important of these. Specifically, the temperature of a turtle’s nest during the middle part of the incubation period has an important influence on the sex of the developing babies.

In general, scientists agree that that temperatures lower than about 29 degrees Celsius (or about 84 degrees Fahrenheit) are likely to produce males, and higher temperatures are likely to produce females.

It’s not totally clear why this is, but it means that as global temperatures rise, there’s a risk that more and more sea turtles could be born female — leaving the population unbalanced.

Jeanette Wyneken, a professor of biological sciences at Florida Atlantic University, and her Ph.D student Alexandra Lolavar, were interested in how changes in both rainfall and temperature could affect sea turtle sex ratios, as global climate change is likely to strongly affect these two variables in many places around the world in the future. Understanding the factors that affect loggerhead sex ratios is important because the turtles are already listed by the federal government as endangered or threatened throughout their habitats, Wyneken said.

Previous laboratory experiments on the effects of environmental conditions on turtle sex ratios had produced some intriguing results that seemed worth following up with a field study, Wyneken said. “When I went back and looked at 10 years of data, we had years where we effectively had 95 to 100 percent female samples…and it turns out all of those years were really hot years,” Wyneken said. “And then the years where we had a high percentage of males were wet years.” These results begged the question of whether rainfall was having a cooling effect on the nests, which was allowing males to develop, or whether it was the moisture itself that was having an effect on baby turtle development.

Wyneken and Lolavar investigated the question by documenting rainfall, sand temperatures and the resulting sex ratios of baby loggerheads on a nesting beach in Boca Raton, Fla. during the 2010 to 2013 nesting seasons (which typically take place between April and October).

They found that rainfall had a slight tendency to cool the sand, particularly at shallow depths — but, in general, “there isn’t very much temperature change at nest level” as a result of rainfall, said lead author Wyneken, unless there’s an especially heavy rainfall event.