Rising global temperatures could shift the balance between males and females in crocodile and alligator populations, potentially leading to a sharp decline in the reptiles’ reproduction rates.

In many reptiles, the temperature of the nest determines the sex of hatchlings: in alligators, temperatures between 32.5ºC and 33.5ºC produce mostly males, whereas temperatures slightly above or below these produce mostly females.

Between 2010 and 2018, Samantha Bock at the University of Georgia in Athens and her colleagues measured the temperature of 86 nests made by American alligators (Alligator mississippiensis) in Florida and South Carolina. The researchers also collected data on daily air temperatures at these sites and found that average nest temperatures were higher during warmer years.

Using estimates of future climate change, the researchers predicted that, if global temperature continues to rise unabated, sex ratios at both sites will become highly male-skewed by the middle of this century. But, by 2100, higher nest temperatures could produce up to 98% females.