Reproductive biology

Crocodiles are territorial. Males are larger than females and will defend territories and compete for mates. Males mate with as many females as possible during the fixed breeding seasons. Crocodiles use a variety of social signals, especially at mating time. These include jawslaps, roaring, dominance, and subordination displays. Females initiate courtship in some species.

All crocodiles lay eggs. Females lay their eggs 40-70 days after mating. The incubation period depends on nest tem

Crocodilians may care for their young for over two years. From left to right, top to bottom: 1. Female lays eggs; 2. Female uncovers nest and helps hatchlings out of their eggs; 3. Hatchlings break out of their shells and make their way to the water's edge; 4. Female carries the newly hatched young in her mouth to the water; 5. An adult provides food for the young, and; 6. Protects the young crocodilians. (Illustration by Wendy Baker)

Crocodilians may care for their young for over two years. From left to right, top to bottom: 1. Female lays eggs; 2. Female uncovers nest and helps hatchlings out of their eggs; 3. Hatchlings break out of their shells and make their way to the water's edge; 4. Female carries the newly hatched young in her mouth to the water; 5. An adult provides food for the young, and; 6. Protects the young crocodilians. (Illustration by Wendy Baker)

perature and is typically 60-90 days. The sex of the developing embryo is determined by temperature; in general, higher temperatures produce males and lower temperatures result in females.

Five species of crocodiles dig holes in the sand, earth, or gravel embankments above the high-water line to lay their eggs. The hole is L-shaped and as deep as the length of the female's hind limbs, which are heavily clawed for digging. The eggs emerge covered with a lubricating mucous, which cushions the brittle shells from cracking as they fall into the nest hole. These species are dry-season nesters whose young hatch with the coming of the rains when many small prey items also emerge.

Nine species of crocodiles are mound nesters. The female gathers together a heap of vegetation, soil, and compost using her legs and jaws. She compacts the mound by crawling over it and then excavates a hole on the top in which to lay her eggs. Mound nesters lay their eggs at the start of the wet season, and the young hatch when the water is highest, a time when there is plenty of small prey.

Female crocodiles (and sometimes males) generally stay near their nest during incubation, repeatedly visiting the site, especially when hatching time approaches. When ready to hatch, the young call with quacking grunts and the parent releases the young from the nest and carries them to the water. Crèche formation is essential for hatchling survival and sometimes both parents guard the young for several weeks or more until they disperse. Adult crocodiles are conditioned to respond to distress calls of the young. Despite parental care, mortality in hatchling crocodiles is generally over 90% due to predators like fishes, crabs, snakes, monitor lizards, raptors, large wading birds, mongooses, foxes, and jackals.

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