Mating and Breeding
For males, the onset of sexual maturity occurs when they are about 3 metres (9.8 ft) long, while for females, it occurs when they reach 2 to 2.5 metres (6 ft 7 in to 8 ft 2 in) in length. This takes about 10 years for either sex, under normal conditions.
During the mating season, males attract females by bellowing, slapping their snouts in the water, blowing water out of their noses, and making a variety of other noises. The larger males of a population tend to be more successful. Once a female has been attracted, the pair warble and rub the undersides of their jaws together. Females lay their eggs about two months after mating.
Nesting is in November or December, which is the dry season in the north of Africa, and the rainy season in the south. Preferred nesting locations are sandy shores, dry stream beds, or riverbanks. The female then digs a hole a few metres from the bank and up to 500 mm (20 in) deep, and lays between 25 and 80 eggs. The number of eggs varies, but averages around 50. Multiple females may nest close together.
The eggs resemble hen eggs, but have a much thinner shell.
Unlike most other crocodilians, female Nile crocodiles will bury their eggs in sand rather than incubate them in rotting vegetation. After burying the eggs, the female then guards them for the three-month incubation period. The sire will often stay nearby, and both parents will fiercely attack anything approaching their eggs. The female will only leave the nest if she needs to cool off (thermoregulation) by taking a quick dip or seeking out a patch of shade. Despite the attentive care of both parents, the nests are often raided by humans and monitor lizards or other animals while she is temporarily absent.
The hatchlings start to make a high-pitched chirping noise before hatching, which is the signal for the mother to rip open the nest. The parents may pick up the eggs in their mouths, and roll them between their tongue and the upper palate to help crack the shell and release their offspring. Once the eggs hatch, the female may lead the hatchlings to water, or even carry them there in her mouth.
Nile crocodiles have temperature-dependent sex determination (TSD), which means the sex of their hatchlings is determined not by genetics, but by the average temperature during the middle third of their incubation period. If the temperature inside the nest is below 31.7°C (89.1°F), or above 34.5°C (94.1°F), the offspring will be female. Males can only be born if the temperature is within that narrow range.
Hatchlings are about 300 mm (12 in) long at birth, and grow that much each year. The new mother will protect her offspring for up to two years, and if there are multiple nests in the same area, the mothers may form a crèche. During this time, the mothers may pick up their offspring either in their mouths or gular fold (throat pouch), to keep the babies safe. The mother will sometimes carry her young on her back to avoid their being eaten by turtles or water snakes. At the end of the two years, the hatchlings will be about 1.2 m (4 ft) long, and will naturally depart the nest area, avoiding the territories of older and larger crocodiles.
Crocodile longevity is not well established, but larger species like the Nile crocodile live longer, and may have an average life span of 70–100 years.
Read more about this topic: Nile Crocodile
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