Crocodiles are egg-laying reptiles. They reproduce by laying hard-shelled eggs, a reproductive strategy shared across all crocodile species. This means crocodiles are oviparous, with embryos developing outside the mother’s body, nourished by the yolk within the egg. This contrasts with live birth seen in mammals.
The Nesting Process
Female crocodiles construct nests for their eggs. Nest types vary by species and habitat, generally falling into two categories: hole nests and mound nests. Hole nesters, such as the Nile crocodile, excavate a cavity in the ground to deposit eggs before refilling it. Conversely, species like the estuarine (saltwater) crocodile build mound nests from plant material, soil, and debris. Mound nests generate heat from decomposition, aiding incubation, while hole nests rely on ambient temperatures.
The female crocodile is responsible for nest construction and egg-laying. This process can take several days or weeks. Eggs are typically laid at night. A single female lays a clutch averaging 12 to 48 eggs, though the number varies by her age, size, and species. Each hard-shelled egg weighs between 50 to 160 grams.
Incubation and Temperature-Dependent Sex Determination
After eggs are laid, incubation typically lasts between 55 to 100 days. The exact duration varies by crocodile species and environmental conditions, particularly temperature. During this time, the female remains close to the nest, guarding it against predators.
Temperature-Dependent Sex Determination (TSD) means the nest temperature during a critical incubation period determines embryo sex. Crocodiles have no sex chromosomes; external warmth dictates whether an egg hatches as male or female. Cooler temperatures (around 30°C) and warmer temperatures (above 33°C) produce female hatchlings, while intermediate temperatures (between 31-33°C) result in males. Specific temperature thresholds vary among species.
Hatching and Early Parental Care
As incubation concludes, hatchlings vocalize from within their eggs, emitting chirping or squeaking sounds. These calls signal other hatchlings, synchronizing emergence, and alert the mother that they are ready to hatch. Each hatchling possesses a temporary “egg tooth” on its snout, a small protrusion used to break the eggshell. This egg tooth typically falls off shortly after hatching.
Upon hearing the calls, the mother crocodile approaches the nest and assists her young, carefully removing debris and helping open struggling eggs, sometimes using her tongue. She then transports vulnerable hatchlings to water. Despite her powerful bite, she delicately gathers multiple babies in her mouth, often in a specialized throat pouch, carrying them safely to a nearby body of water. This initial protection is important for hatchlings, as they are highly susceptible to predators, including larger crocodiles. The mother typically guards her offspring for several weeks to months after hatching.