Turtle nest temperature decides whether hatchlings are male or female

Most turtles don't get their sex the way mammals do. There aren't sex chromosomes doing the deciding at fertilization. The temperature of the nest during a key stretch of incubation is what makes hatchlings male or female. It's called temperature-dependent sex determination.

For sea turtles, NOAA puts the split roughly here: eggs that incubate below about 81.9°F (27.7°C) tend to produce males. Eggs above about 88.8°F (31°C) tend to produce females. Temperatures in between make a mix. Warmer sand generally means a higher share of females.

That's also why nesting-beach researchers worry about climate. If the sand stays too hot, you can get heavily female-biased hatchling years.

Source: NOAA Ocean Service — "What causes a sea turtle to be born male or female?"

https://oceanservice.noaa.gov/facts/temperature-dependent.html