Considerable variation exists throughout the range of the Nile Crocodile. Generally, it is a large crocodilian, averaging 5 m in length but reportedly reaching 6 m in rare instances. There are dubious reports of 7 m animals having existed, but these are hard to verify.
There is some evidence that Nile Crocodiles in cooler countries reach slightly smaller adult sizes (4 m). There are two known population of dwarf Nile crocodiles living on the extreme limits of the species' range, in Mali and even the Sahara Desert! Due to suboptimal conditions, adults average between 2 and 3 metres. Juveniles are dark olive brown with black cross-banding on the tail and body. This banding becomes fainter in adults.
Although the juveniles are generally restricted to eating small aquatic invertebrates and insects, they soon move onto larger vertebrates such as fish, amphibians and reptiles. Adults, however, can potentially take a wide range of large vertebrates, including antelope, buffalo, young hippos, and large cats. Fish and smaller vertebrates often form the greatest part of their diet, however they have a reputation as being man-eaters, they have probably killed more people than all other crocodilian species combined.
Along with hippos and lions, crocodiles account for perhaps a few hundred deaths and disappearances each year, although exact figures are very hard to verify. Nile crocodiles will also often scavenge from carcasses, together with a number of other animals, all of which seem to tolerate each others' presence. Several prey animals have been found wedged under submerged branches and stones, leading to reports that the crocodiles store unwanted prey here until a later date.
Some claim that it is necessary for the prey to decompose before the crocodiles are able to tear portions of flesh off, but this is unlikely to be true. The flesh may become softer if the prey remains in water after death, but crocodiles will certainly avoid rotting meat. When feeding, a number of individuals will hold onto a carcass with their powerful jaws whilst twisting their bodies.
The anchorage provided by the other individuals allows large chunks to be torn off for easier swallowing. Other cooperative feeding behaviour has been reported, such as the action of many animals to cordon off an area of water to concentrate fish within. A hierarchy of feeding order is often observed in such situations, with more dominant animals feeding first.
Groups of Crocodiles will often move onto land to scavenge from kills made up to several hundred metres from the water. Adults have also been observed fishing using their bodies and tails to corral the fish towards the bank where they are concentrated and picked up with a sideways snatch of the jaws.
This species digs hole nests up to 50cm deep in sandy banks, several metres from the water. These may be in close proximity to other nests. Timing of nesting behaviour varies with geographic location, it takes place during the dry season in the north, but at the start of the rainy season further south, usually from November through to the end of December.
Females reach sexual maturity around 2.6 m, males at around 3.1 m. Females lay around 40 to 60 eggs in the nest, although this number is quite variable between different populations. Females remain near the nest at all times. Incubation time averages 80 to 90 days (ranges from 70 to 100 days), after which females open the nest and carry the juveniles to the water.
Both males and females have been reported to assist hatching by gently cracking open eggs between their tongue and upper palate. Hatchlings remain close to the juveniles for up to two years after hatching, often forming a creche with other females. As with many Crocodilians, older juveniles tend to stay away from older, more territorial animals.
Despite the vigilance of the female during the incubation period, a high percentage of nests are raided by a variety of animals, from hyaenas and monitor lizards to humans. This predation usually occurs when the female is forced to leave the nest temporarily in order to thermoregulate by cooling off in the water.
Social behaviour in Nile Crocodiles is often underestimated, although there are many aspects still poorly understood. It has been observed that social status may influence an individual's feeding success, with less dominant animals tending to eat less in situations where they come into frequent social contact with other, more dominant individuals.
Where they are found
South Africa, Botswana, Egypt, Ethiopia, Ivory Coast, Kenya, Madagascar, Mozambique, Namibia, Somalia, Swaziland, Zambia, Zimbabwe.
Given the wide distribution range, a number of population differences have been observed, and several subspecies proposed. These are rarely differentiated in the literature, however, and they are not officially recognised. C. n. africanus (East African Nile Crocodile), C. n. chamses (West African Nile crocodile), C. n. corviei (South African Nile crocodile), C. n. madagascariensis (Malagasy Nile crocodile, Malagasy alligator, Croco Mada), C. n. niloticus (Ethiopian Nile crocodile), C. n. pauciscutatus (Kenyan Nile crocodile, Kenya alligator, Kenya caiman), C. n. suchus (Central African Nile crocodile).