Sea turtles journey from the ocean to the beach to deposit their eggs, a process known as nesting. This ritual requires the female to leave the safety of the water and crawl onto the sand to create a secure incubation site. For most species, including the Loggerhead, Green, and Leatherback turtles, this vulnerable process takes place almost entirely under the cover of darkness. This nocturnal behavior is a deep-seated adaptation that addresses various biological and environmental pressures unique to the nesting environment.
The Specific Timing of Egg Laying
Most individual sea turtle nesting occurs after sunset and concludes before dawn. For instance, the solitary Loggerhead turtle is frequently observed nesting between the hours of 10 P.M. and 3 A.M. The entire sequence, from crawling out of the surf to returning to the ocean, typically takes between one and three hours to complete.
While nighttime nesting is the rule, exceptions occur during specific mass nesting events. The Olive Ridley and Kemp’s Ridley turtles, both from the genus Lepidochelys, participate in synchronous nesting events known as “arribadas”. While Olive Ridley arribadas primarily happen at night, the Kemp’s Ridley is one of the few species known to regularly nest during daylight hours. This daytime behavior is thought to be an evolutionary strategy where the sheer number of turtles overwhelms potential predators.
The Physical Nesting Process
The nesting sequence begins when the female emerges from the surf and crawls above the high tide line to select a suitable site. She may crawl a significant distance and make multiple attempts before settling on a spot she deems safe enough to dig. Once a location is chosen, the turtle uses her front flippers to sweep and clear a shallow depression, known as “body pitting”. This action helps anchor her body and creates a starting point for the egg chamber.
The next stage requires the female to excavate the egg chamber, a deep, flask-shaped hole. She uses her rear flippers with alternating motions to dig straight down into the sand. The depth of this chamber is limited only by the reach of her back flippers, often extending two feet or more. After the chamber is completed, the female enters a trance-like state and deposits her clutch, which can contain anywhere from 50 to over 100 eggs, depending on the species.
Following the deposition of the eggs, the female carefully covers them by scooping sand back into the chamber using her rear flippers. She then compacts the sand over the eggs by tamping it down with her shell and flippers. The final stage is camouflaging, where she uses all four flippers to throw sand across a wide area. This vigorous scattering motion disguises the exact location of the nest before she finally crawls back toward the ocean.
Environmental Drivers Behind Nocturnal Nesting
The primary reason most sea turtles nest at night is the reduction in thermal stress. Daytime temperatures on beaches can be extreme, and the effort of crawling and digging on land can quickly lead to overheating for a cold-blooded reptile. By nesting at night, the female avoids the most intense heat of the day, which helps conserve the energy needed to complete the demanding nesting process.
Predation avoidance is another selective pressure favoring darkness for nesting. The female sea turtle is highly vulnerable to predators like coyotes, raccoons, and wild dogs when she is slowly moving on land. The cover of night makes it much more difficult for these terrestrial predators to locate the nesting female and the freshly laid eggs. Nesting females also exhibit a tendency to select the darkest and quietest areas of a beach, indicating an instinct to avoid disturbance and detection.
The timing of nesting is also closely linked to the ocean’s tides, as females often emerge near high tide. Nesting during a high tide minimizes the distance the turtle must crawl up the beach to find a site above the water line. This reduces the energy expenditure for the female and decreases the amount of time she spends exposed on the sand. Furthermore, mass nesting events like the Olive Ridley arribadas frequently occur around the darkest nights of the lunar cycle, specifically near the new moon, to maximize the benefit of darkness.