BOCA RATON, Fla. — The struggle to save the already endangered green sea turtle faces a new challenge. The turtles nearly vanished 40 years ago in Florida, but a coordinated effort by conservationists, government agencies and volunteers brought the animals back from the brink. Now, the males of the species seem to be disappearing, CBS News' Mark Strassmann reports.

In a beachfront ritual that dates back more than 100 million years, CBS News came upon a 300-pound green sea turtle covering her beach nest, burying maybe 100 eggs or more.

Biologist Jeanette Wyneken directs Florida Atlantic University's marine lab, and has studied Florida's sea turtle population since 2002. She's alarmed by what she doesn't see in her tanks of hatchlings.

"We're seeing fewer and fewer and fewer years where we find males, so seven out of the last ten years, we have not found any males," she said. "Not a single one."

Rising temperatures is impacting the population of male sea turtles. CBS News

It's not genetics that determine a sea turtle's sex, it's the temperature of the sand. The tipping point is roughly 85 degrees for a species that's predominantly female.

"If it's too warm you don't get boys. If it's too cool, you don't get girls. So it's the hot chicks and the cool dudes," Wyneken said.

She says the nests are getting warmer because of the weather and climate change.

As Florida's beaches get hotter, species are showing signs of shutting down -- sea turtles, and possibly alligators, another reptile whose eggs skew female and whose sex is determined by nest temperatures.

On a rooftop at the University of North Florida, biologist Adam Rosenblatt has built 20 nests, of 20 alligator eggs each. Plastic will artificially warm the nests by five-point-five degrees, which is how much hotter north Florida's expected to be by the end of the century.

"If it's happening in sea turtles, my thought was it could be happening in alligators as well and it could throw off that balance between males and females," Rosenblatt said.

Back in Wyneken's lab, she uses a mini-camera to determine their sex after they reach six weeks old.

"So I have to wait until they're big enough for me to sort of – look under their skirts," Wyneken said.

Monday night, her team released hundreds of hatchlings into the sea, to the admiration of dozens of turtle fans. She knows the odds are already long for this prehistoric species, more so now that climate change is in play.

"There's some resilience in there that we scientists may not have discovered and then there's a part of us that says, 'Things are changing so fast compared to what's happened in the past, that resilience may not be enough,'" Wyneken said.

Sea turtles don't reach sexual maturity until they're at least 25 years old, so the impact of disappearing male hatchlings may not be known for another generation.