Common names
Nile crocodile, Mamba, Garwe, Ngwenya
Name etymology
> Crocodylus is derived from the Greek krokodeilos which means literally "pebble worm" (kroko = pebble; deilos = worm, or man) referring to the appearance of a crocodile.
> niloticus means "of the Nile" (Nile River, Africa)
Subspecies (Proposed)
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.
Suggested subspecies: 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)
The Nile crocodile is a member of the reptile class and is a survivor of the Archosaria, a group that included dinosaurs. They have not changed much over millions of years. They are more advanced than other modern day reptiles in that they have a four-chambered heart like mammals and can adapt their behavior to survive.
They have a lifespan of 70 to 100 years.
Habitat
Wide habitat preferences, reflecting their success and distribution- e.g. lakes, rivers, freshwater swamps, brackish water. Sub-adults disperse into different habitats, away from breeding areas, when they reach a length of approximately 1.2 m. Nile crocodiles modify their habitat by digging dens (usually with their snouts and feet) into which they retreat from adverse conditions such as temperature extremes.
Appearance
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 (eg. South Africa) 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.
The snout is long and broad and ends in nostrils which can close underwater. The eyes have a third eyelid which protect them while underwater. The eyes, ears, and nostrils are found on the same plane on the top of the head, allowing the crocodile to be completely submerged underwater while still being able to see, smell, and hear. The teeth are long and conical. The teeth on the top jaw are in line with the bottom jaw, a feature which distinguishes all crocodiles from alligators. The fourth lower tooth is larger than the others and can be seen when the mouth is closed. Nile crocodiles have 66 teeth.
Diet
Although the juveniles are generally restricted to eating small aquatic invertebrates and insects, they soon move onto larger vertebrates (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. As with C. porosus, they have a reputation as being man-eaters, although probably kill 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. They have a rather well-known relationship with several species of birds (e.g. spur-wing plover, called "trochilus" by Herodotus) which are reputed to pick pieces of meat from between the teeth of the crocodiles as they gape - the birds gain a meal, the crocodiles have their teeth cleaned of scraps they could not eat themselves. Whether such a mutual relationship actually exists is hard to determine from the literature and anecdotal reports, but seems more likely to be opportunistic rather than symbiotic.
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. A few lone individuals have been reported to wedge prey between branches in order to provide the anchorage necessary for such actions to be effective, which could even be claimed to be a form of primitive tool use.
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. 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.
Breeding
Males become sexually mature at 10 ft (3 m - 10 years of age) and females at 6.5 ft (2 m - 10 years of age). The breeding season is July, where they mate in shallow water. The female lays 30-80 eggs in a nest of rotting vegetation near the water's edge. The eggs hatch after an incubation of 2-3 months. If the nest was below 85° F during this period, then all the hatchlings are female. Above 95° F - male. Between 85° F and 95° F - both male and female. When it is time to hatch, either parent helps to open the eggs by cracking them in its mouth. They are then carried to the water. They remain in the water for several weeks. Hatchlings are 12 in (30 cm) long and are dark olive green with darker crossbandings on the body and tail.
This species digs hole nests up to 50 cm 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.
Crocodiles are not solitary predators as often imagined, but social creatures. Cows of some species protect not only their hatchling young but offspring from the previous year. Nile Crocodile bulls also respond to distress calls of their young., crocodiles convey social messages with motions, odors, postures, by touch and with sounds. Nile Crocodiles produce at least six different vocal signals. Both cow and bull Nile Crocodiles maintain territories, especially during breeding season.
Enemies
Few animals are willing to prey on the Nile crocodile except for other Nile crocodiles and humans. They have been overhunted by humans for their skin, which is good for tanning, and their meat. Habitat destruction also dwindles their numbers. The young are preyed upon by Nile monitor lizards, marabou storks, herons, ibises, turtles, and catfish. Nile crocodiles are not endangered.
The trade of the Nile crocodile has become an environmental concern especially in the Republic of Tanzania. Crocodile skins are being exported from Tanzania in large quantities due to the high demand for leather goods. The Nile crocodile skins are being exported for the luxury leather goods market including shoes, handbags and belts, especially to Japan, Italy and France.
However, this trade has caused the Nile crocodile to be classified as an endangered species. As a result, the United States along with 120 other countries throughout the world have joined in signing the Convention on International Trade and Endangered Species of World Fauna and Flora (CITES) treaty in 1973 to ban skins from endangered or potentially endangered species, such as the Nile crocodile, from being traded. In April 1994, the classification of the Nile crocodile was changed from endangered to threatened as a result of various acts and treaties protecting this species.
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