By Stacey Venzel
Nest-building is not just a task left to the birds. While turtles do not pick up sticks to create a nest, they do use their back feet to dig holes in the ground.
Whether the eggs are laid on land or in water, turtles make sure to choose the best spot for their babies before committing to a nest site. Some even go as far as to dig false nests or produce unfertilized protective eggs.
All but two species lay their eggs on the land, ranging from sand to dirt. Gopher tortoises bury their eggs in front of their burrows whereas sea turtles dig on beaches and other aquatic turtles on banks. In suburban sprawl areas encroaching on a turtle’s natural domain, species in lakes and ponds sometimes resort to nesting in golf courses and home gardens.
The Central American river turtle excavates an egg chamber where the soil is sopping wet near the waterline, sometimes so close that the eggs are underwater when the river level rises with heavy rain. The Northern Australian snake-necked turtle is the only species that relies completely on underwater egg homing, opting for shallow areas where the eggs hatch when exposed to air due to decreased water levels. Unluckily for these hatchlings, they are stuck below the dry soil until a year later when the rainy season returns to moisten the sun-cooked ground.
THE PERFECT NEST
Females do not give up when it comes to finding the ideal location for a nest. Especially noticeable in sea turtles, the soil particles have to be small enough for air to filter around the packed porous eggs because hatchlings breathe through their shelled cocoon. Humidity is important, too, to prevent the eggshell from drying out. Females also make sure accurate temperature and predator protection are in check before laying the eggs.
A few turtles dig more than one nest when laying a single clutch of eggs. Florida cooters have a main nest and one to two holes next to it called satellite nests. Only two or so eggs are laid in these extra nests, presumably tricking predators from devouring the majority of the eggs. Other turtles, like the North American box turtle, dig empty nests, abandoning them when they determine the site harbors unfavorable nesting conditions.
At times, some of the eggs expelled by a female are infertile. Leatherbacks, unique in this attribute among sea turtles, purposely deposit unfertilized eggs atop fertile eggs before covering the nest. Based on the large size of leatherback eggs, it is believed that these fake eggs allow for increased airflow to the developing embryos below.
Karen Eckert, David Gulko, Sea Turtles: An Ecological Guide (Honolulu, Mutual Publishing, 2004), 64-66.
Carl J Franklin, Turtles: An Extraordinary Natural History 245 Million Years in the Making (St. Paul, Voyageur Press, 2007), 33-34.
Whit Gibbons, Judy Greene, Turtle: The Animal Answer Guide (Baltimore, The John Hopkins University Press, 2009), 61, 69.