Painted turtles, common in Minnesota, crawl from the pond behind our house each spring to find a spot to lay eggs. They often choose the bare ground alongside our driveway. That patch gets sunlight, apparently just enough to suit the turtles.
The sex of turtles is determined by the temperature at which the eggs incubate, there in the soil. Weather is vague, so temperature varies year to year, egg to egg, and sexual balance is maintained.
A few weeks later, I will see the hole the turtle dug opened, rubbery fragments of turtle-egg shell scattered. I keep hoping for a moment of dumb luck allowing me to watch the hatch.
All turtles bury their eggs, and let the sun tend to the hatching.
Right now, on the island of Cape Verde, sea turtle eggs are hatching. They have incubated in holes dug in the sandy shores of the island by female turtles.
Naturalists who monitor the turtles are finding that most and sometimes all of the new turtles are girls, the decision on sex made by a warming climate.