Check out our Nile Crocodile Gallery.
It is almost unbelievable that a dinosaur which evolved some 180 million years ago and which appears so cold and uncaring could set an example to mothers around the world. The Nile crocodile (Crocodylus niloticus), the only species of crocodile to occur in South Africa, is a powerful aquatic hunter reaching a length of 5,9 m and weighing as much as 500 kg. But in spite of its size and aggressive appearance it can lead a life fraught with anxieties.
On the eastern side of South Africa, in subtropical KwaZulu Natal, crocodiles breed once a year, the female laying her eggs from late September to mid December. The hot summer months, with their high humidity levels, are ideal to incubate her eggs at temperatures between 28 and 34 degrees C. The sex of her offspring is determined by the incubation temperature, 32 degrees C and above producing males while lower temperatures produces females.
Courtship between males and females starts some 4 to 5 months earlier and peaks during August and September. During this period the larger males move to the nesting areas where they compete for dominance and establish their territories. The dominant males attack and chase away smaller suitors and, in an attempt to attract the females, perform elaborate courting displays in the water. A male crocodile may sometimes need to court a female for several days before she submits to his advances, while at other times it is the female that initiates the courtship. Dominant males may mate with as many as 4 or 5 females during the season, the mating taking place in the water.
Nests are generally sited in sand banks above the high water level and the female makes her way to the nesting grounds a week or more before she is due to lay, where over several nights she digs test holes to check the suitability of the soil temperature and its water content. After she has found a site that is to her liking, she digs a hole in the sand to a depth of about 45 centimetres, using her hind feet to scrape the earth backwards. She then moves over the hole and starts to lay her eggs, the number varying from 20 to 80 depending on her age. After she has finished laying, she scrapes the soil back over the nest and stamps it down, again using her hind feet.
The egg incubation period lasts between 84 and 90 days and during this time the mother lies close to her nest to defend it, not eating and only moving away for short periods to drink. When the young are ready to hatch they begin squawking, which is a signal to her to open the nest. The hatchlings emerge, having split open the shell of their eggs by using a special little tooth found at the end of their snout. The mother gently picks them up together with any unhatched eggs into her mouth, their weight forming a pouch in her throat that can hold up to about 20 eggs and young. She carries the hatchlings to the water and releases them by opening her jaws below the surface and moving her head from side to side. The female helps any of her brood that have not managed to hatch successfully by rolling the eggs gently between her tongue and palate to break the shells.
The small crocodiles remain close to their mother over the next few weeks, often lying on her back to bask in the sun. They stay together by uttering contact calls and if need be high-pitched distress calls, which their mother or any other female in the area responds to instantly. During this period they eat mainly insects and keep close to the reeds and overhanging vegetation on the riverbanks for protection against predators. As they grow their diet changes and they start catching fish and birds and after about 6 weeks they become independent and move away from the nursery. At this point the parents leave the area, their search for food by this stage being a priority, especially for the mother who has not eaten for months.
In spite of the dedicated vigil at the nest by both the male and female crocodile, their eggs and young are constantly under threat of death. Conditions in the nest such as changes in temperature and humidity or flooding due to heavy rainfall or waves can affect the successful incubation of the embryos. In addition, there is a high predation of the eggs and hatchlings by mongooses, baboons, otters, water monitors and birds of prey. Man, however, remains the greatest threat, due largely to competition for the same habitat, to degradation of the environment and to poaching. In view of the seemingly endless hazards faced by the eggs and young, it is not surprising that only an estimated 2 percent survive to reach maturity at about 10 to 12 years of age. Adult crocodiles, given half a chance, can reach the age of 70 years or more.
In KwaZulu Natal the Nile crocodile occurs from the Mozambique border in the north to the Tugela River in the south. Large populations exist in the Isimangaliso Wetland Park and in the Hluhluwe iMfolozi Park, while smaller groups are found on the Pongola River flood plain. However, in spite of the protection offered to the crocodile in these areas, it remains vulnerable and it would be a travesty of justice if this dinosaur were to face extinction at this stage of its existence, 180 million years on.
Be sure to check out our Nile Crocodile Gallery.
© 2018 Roger and Pat de la Harpe. All Rights Reserved