Sea turtles lay their eggs on sandy beaches above the high-water mark, typically on the berm or the first dune inland from the tide line. Every species nests on land, and no sea turtle lays eggs in the ocean. Females crawl ashore, dig a flask-shaped chamber with their back flippers, deposit their eggs, cover the nest, and return to the sea, all in one to three hours.
What makes this remarkable is that most females return to nest on or very near the same beach where they themselves hatched, sometimes traveling thousands of miles across open ocean to get there.
How Turtles Find Their Way Back
Sea turtles use a navigation system built into their biology. As hatchlings, they imprint on the unique magnetic signature of their home beach. Earth’s magnetic field varies slightly from place to place, and turtles can detect these differences with enough precision to relocate a specific stretch of coastline years or even decades later. Population genetic studies confirm this: distinct turtle populations map closely onto the magnetic fields present at their nesting beaches, meaning turtles that nest together share ancestry because their mothers and grandmothers all homed to the same magnetic address.
This magnetic navigation guides the bulk of the long-distance journey. Once close to shore, turtles likely refine their approach using other cues like water chemistry, smell, and visual landmarks.
What Makes a Beach Suitable
Not every sandy beach works. Turtles need coarse, well-drained sand with particle sizes generally in the 250 to 2,000 micrometer range. The sand must hold enough moisture to keep the eggs from drying out but not so much that the nest floods. Healthy nest sand has a water content between 2% and 10%. When sand drops below 1% moisture, embryos lose water faster than they absorb it, and hatching success drops sharply.
Beach shape matters too. Females look for a stretch of sand wide enough to nest above the high-tide line, with a gentle slope they can physically climb. Beaches backed by vegetation or low dunes are ideal because the sand is more stable and less likely to wash away during storms. Both mineral sand beaches (like those in mainland Australia) and biogenic beaches made of broken coral and shell fragments (like island rookeries) support nesting, as long as the grain size and drainage fall within the right range.
The Nest Itself
A female sea turtle digs her egg chamber entirely with her rear flippers, sculpting a vase-shaped hole roughly 60 to 100 centimeters deep. Green turtles, one of the most studied species, dig nests averaging about 79 centimeters deep, though a large clutch of 110 eggs may sit in a chamber over 92 centimeters down while a small clutch of 20 eggs may need only 76 centimeters. Flatback turtles, which are smaller, dig shallower nests averaging around 53 centimeters. Leatherbacks, the largest species, create chambers about 76 centimeters deep divided into a washbowl at the top and a deeper incubation chamber below.
Clutch sizes vary by species and individual. Green turtles lay between 40 and 120 eggs per nest. A single female may nest multiple times in one season, returning to the same beach every 10 to 14 days to lay another clutch before heading back to her feeding grounds.
Where in the World Turtles Nest
Sea turtles nest across tropical and subtropical coastlines worldwide, with some species ranging into warm temperate zones. Leatherback turtles have the widest distribution of any reptile, nesting primarily in Mexico, Costa Rica, Indonesia, Papua New Guinea, and the Solomon Islands. Western Pacific leatherbacks show an unusual pattern, nesting in both winter and summer months. Green turtles nest throughout the Caribbean, along the coasts of Central America, across the Indian Ocean, and at massive rookeries in Australia, including Raine Island, the largest green turtle nesting site on Earth.
In the United States, nesting season stretches from roughly April through September on most Atlantic and Gulf Coast beaches, with loggerheads dominating in the Carolinas and Florida and green turtles nesting in smaller numbers further south. In Hawaiʻi, green turtles nest from mid-April through September, though some nesting extends into December. All species nest at night, likely to avoid heat stress and reduce exposure to predators.
Sand Temperature Decides the Sex
One of the most consequential features of a nesting site is its temperature. Sea turtles have temperature-dependent sex determination, meaning the warmth of the sand during incubation controls whether hatchlings develop as male or female. Eggs incubated below 27.7°C (about 82°F) produce males. Eggs incubated above 31°C (about 89°F) produce females. Temperatures between those thresholds yield a mix.
This is why nest location on a beach matters so much. A nest closer to the waterline sits in cooler, wetter sand and tends to produce more males. A nest higher up in dry, sun-exposed sand runs warmer and skews female. Shaded areas near vegetation can also keep temperatures lower. As global temperatures rise, many nesting beaches are producing overwhelmingly female hatchlings, which raises long-term concerns about breeding populations.
Threats to Nesting Beaches
The beaches sea turtles depend on are shrinking. Global sea levels have risen 1.5 to 1.9 millimeters per year over the past century, accelerating to 2.8 to 3.6 millimeters per year in the last two decades. Projections suggest sea levels could rise between 0.5 and nearly 1 meter by 2100 under current emission trends, with some estimates reaching 2 meters. For nesting turtles, the critical problem is “coastal squeeze,” where rising water on one side and roads, buildings, or seawalls on the other leave less and less sand between them. Studies of barrier island nesting sites in the southeastern U.S. predict losses of 1% to nearly 7% of available nesting area by 2100, with the narrowest and lowest-lying stretches disappearing first.
Artificial light is another major threat. Coastal lighting deters females from coming ashore and concentrates nests in darker, often less suitable areas. The effect on hatchlings is even more dramatic. Hatchlings naturally orient toward the brightest horizon, which over the ocean is the sky reflecting off the water. Artificial lights reverse that cue. In experiments on Lanyu Island in Taiwan, 72% of green turtle hatchlings exposed to white light crawled in the wrong direction. Nearly 90% of hatchlings on the island failed to find the sea under ambient light pollution conditions. Yellow light caused significantly less confusion, with only 17% of hatchlings misdirected, because turtle eyes are far less sensitive to long-wavelength light. Red light needs to be roughly 600 times brighter than blue light before hatchlings respond to it at all, which is why coastal communities near nesting beaches increasingly use amber or red outdoor lighting during nesting season.
Simple light shields also make a measurable difference. In tests, an unshielded white light illuminated the beach up to 12 meters from the source. Adding a shield cut that range in half and reduced light intensity by nearly 90%.