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Britton 2009

Created By: Roland Ortega
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This information was most-recently updated January 2009 and is considered up-to-date. Please contact me directly regarding updates or corrections.

Nile crocodile, Mamba, Garwe, Ngwenya
> {1}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)

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)

Angola, Benin, Botswana, Burkina Faso, Burundi, Cameroon, Central African Republic, Chad, Congo, Egypt, Ethiopia, Equatorial Guinea, Gabon, Gambia, Ghana, Guinea, Guinea Bissau, Ivory Coast, Kenya, Liberia, Madagascar, Malawi, Mali, Mozambique, Mauritania, Namibia, Niger, Nigeria, Rwanda, Senegal, Sierra Leone, Somalia, South Africa, Sudan, Swaziland, Tanzania, Togo, Uganda, Zaire, Zambia, Zimbabwe. Fairly recently extirpated from Israel, and less recently (beginning of the 19th century) from the Cormoros islands (thought to be due to an increase in aridification and thus a decrease in suitable habitat).

{3}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.

CITES: Appendix I, except 1. Botswana, Ethiopia, Kenya, Malawi, Mozambique, South Africa, Tanzania, Zambia, Zimbabwe (Appendix II ranching); 2. Madagascar, Uganda (Appendix II annual quota)
IUCN Red List: LRlc (LOW RISK, LEAST CONCERN, may be threatened in some parts of range)
Estimated wild population: 250,000 to 500,000
Summary: Wide distribution coupled with healthy populations and successful management in many areas. A few areas are poorly surveyed or with depleted populations

[click on image for enlargement]
{4}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.

5 pre-maxillary; 13-14 maxillary; 14-15 mandibular
{5}Total no. of teeth = 64-68
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Sub-adult head amongst a group Head of adult from above (b&w) Adult basking on grass
Detailed adult head portrait (b&w)
{6}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.

{7}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.

{8}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.

{9}When considering its total distribution and status, the Nile crocodile is not considered seriously endangered per se, although in some areas it is badly depleted and in danger of being extirpated from some countries. Extensive population surveys in some areas have contributed to sustainable-yield management programs, mainly in southern and eastern African countries. These have been part of the monitoring necessary for those countries trying to establish sustainable use programs encouraged by IUCN and CITES. Central and western countries have seen much fewer population surveys conducted, and in general most countries (two thirds of African countries) have very little information regarding status.

After a population decline around the middle of the century due to over-hunting, legal protection has resulted in significant recoveries in several areas, and large populations can now be found (e.g. Botswana, Ethiopia, Kenya, Zambia, Zimbabwe). However, even with the lack of survey information, it appears that numbers in central and western countries are faring badly. This may be partly due to habitat differences, and the presence of two other sympatric species of crocodile (C. cataphractus and O. tetraspis). Humans do come into conflict with C. niloticus in several areas (e.g. mortality due to crocodiles has been reported frequently in Tanzania), and this fuels the need to establish more sustainable-yield management programs, together with educational programs. The skin from this species is considered to be a 'classic' skin, in that high-quality leather is obtainable without blemish-causing osteoderms reducing its value. Commercial utilisation is widespread, therefore, and many successful management programs have been established (e.g. Zimbabwe, South Africa). These have mainly been set up in conjunction with CITES, with the emphasis being placed upon ranching programs. Countries which still have certain quotas that can be harvested from the wild are moving towards establishing their own ranching programs (e.g. Madagascar). These initiatives are perhaps responsible for the lack of illegal trade in this species, which is currently considered to be insignificant.

{10}Further conservation goals should include detailed surveys in western and central African countries, and the nurturing of newly-established management programs. Ecological research into population dynamics should also provide valuable information for sustainable-yield programs.
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