Turtles begin their lives by hatching out of eggs buried by their mothers in a patch of sun-warmed sand or soil to accommodate the incubation process. After several months of development, hatchlings of most species begin digging their way to the surface as they emerge from their eggs – though other species remain below ground through the winter and emerge the following spring.
Most turtles exhibit a phenomenon called temperature-dependent sex determination. This means that the incubation temperature of the eggs, rather than the genetic material of the parents, determines whether the young will be male or female. For some species, incubation temperatures at the high end of the tolerable range produce mostly male offspring, while incubation temperatures at the low end of the tolerable range primarily produce females. In other species, high and low temperatures produce females, and temperatures intermediate between the two extremes produce males.
Different turtle species practice divergent reproductive strategies with regard to offspring number. Some turtles mature slowly and produce gigantic egg clutches for decades. Other species mature relatively quickly but produce small egg clutches. Species size also plays a role in this pattern: Females of large species typically deposit more eggs than females of smaller species do.
Eggs and Egg Teeth
Some turtles produce pliable, leathery eggs, much like those snakes produce, while others produce hardened eggs somewhat similar to bird eggs. Regardless of the shell’s consistency, neonatal turtles emerge from their shells with the help of an egg tooth, which will fall off shortly after hatching. The young of some species tend to hatch all at once. This is likely an adaptation designed to saturate the area with young, thereby satiating predators with enough food to allow a few individuals to survive.
Some turtle breeders dig up eggs and incubate them artificially, while others leave eggs buried and allow them to progress naturally. To incubate them artificially, breeders place the eggs in a special heated box tat maintains a consistent temperature and humidity. Unlike bird eggs, which must be rotated regularly, turtle eggs must be left to incubate in the orientation in which they were deposited. If the breeder rotates the eggs, the embryos – which attach to the inside of the shells and therefore remain stationary – may drown.