Nile crocodile (Crocodylus niloticus)

KingdomAnimalia
PhylumChordata
ClassReptilia
OrderCrocodylia
FamilyCrocodylidae
GenusCrocodylus (1)
SizeTotal length: up to 6 m (2) (3)
Hatchling length: c. 31 cm (4)
Weightup to 1000 kg (2)

The Nile crocodile is classified as Least Concern (LC) on the IUCN Red List (1). All populations are listed on either Appendix I or II of CITES (5).

One of the largest of all crocodilians (6), the Nile crocodile (Crocodylus niloticus) is a supremely adapted aquatic predator, with a streamlined body, a long, powerful tail, webbed hind feet, and long, powerful jaws, ideally suited for grabbing and holding onto prey (7). The eyes, ears and nostrils are located on top of the head, allowing the crocodile to lie low in the water, almost totally submerged and hidden from prey. A special valve at the back of the throat allows the mouth to be opened to catch and hold prey underwater without water entering the throat (7).

In addition to a good sense of smell and excellent night vision, the Nile crocodile also possess sensory pits in the scales along the side of the jaw, used to detect movement and vibrations in the water. Like all true crocodiles, the enlarged fourth tooth on the lower jaw is clearly visible when the mouth is closed, a feature which distinguishes this group from other crocodilians, such as alligators (7).

The body of the adult Nile crocodile is a grey-olive colour, with a yellowish belly, while the juvenile is more greenish or dark olive-brown, with black cross-banding on the tail and body, which becomes fainter in adults (2) (3). In general, the male Nile crocodile grows larger than the female (6).

The Nile crocodile has a wide distribution throughout sub-Saharan Africa and is also found on Madagascar (1) (6). However, it has been eliminated from some former parts of its range, including the Mediterranean coast, Israel and Jordan (2) (6).

The Nile crocodile inhabits a wide range of aquatic habitats, including large freshwater lakes, rivers, freshwater swamps, coastal estuaries and mangrove swamps (2) (3) (6). Different age groups may use different habitat types, with sub-adults dispersing away from breeding areas on reaching a length of around 1.2 metres (3) (6).

The Nile crocodile shows a shift in diet with increasing body size. Young individuals usually feed on insects, small fish, amphibians and crustaceans, the diet changing to include more vertebrates, including fish, turtles, birds and mammals, as the individual matures (3) (6) (7). The largest Nile crocodiles are capable of taking prey up to the size of antelope, buffalo, zebras and wildebeest, dragging the prey into the water and spinning the body around to tear off chunks of flesh (2) (3).

Like other reptiles, the Nile crocodile controls its body temperature by entering the water when hot and basking in the sun when cool (6), and basking crocodiles are often a common sight along riverbanks. It may also dig dens, which it uses to retreat from adverse environmental conditions (3). The Nile crocodile has quick reflexes and is a surprisingly fast runner on land (2) (6), though it may tire quickly (7).

Breeding usually takes place during the dry season (6) (7), though the exact timing varies with location (3). Mating takes place in the water. The nest is a hole, up to 50 centimetres deep, dug by the female into a sandy bank, several metres from the water (2) (3) (6). The female Nile crocodile is an attentive parent, and, after laying up to around 60 eggs, will cover the nest with sand and guard it for the entire incubation period, around 90 days (2) (3) (4).

Sex in the Nile crocodile is determined by the temperature at which the eggs are incubated, with females produced below 31 degrees Celsius, and males at above 31 to 34 degrees Celsius (8). When about to hatch, the young make a “peeping” noise, which encourages the female to excavate the nest. The female then gathers the hatchlings in her mouth and transports them to the water, where they remain in a group for several months, protected by the female (2) (4) (7). Amazingly, the Nile crocodile’s powerful jaws can be used incredibly gently, and the female can even help hatchlings emerge by carefully rolling and squeezing the eggs in her mouth. However, despite this care and vigilance, nests may be raided by a variety of other animals, and hatchling crocodiles are very vulnerable to predation (3) (7).

Young female Nile crocodiles reach sexual maturity at a body size of around 2.6 metres, and males at 2.7 to 3.1 metres (3) (9), achieved at around 12 to 15 years old (2). The Nile crocodile can be long-lived in the wild (6).

The social behaviour of the Nile crocodile is often underestimated (3). Males are territorial, patrolling and defending territories which may encompass a length of shoreline and extend up to 50 metres out into the water (4). Co-operative feeding behaviour has also been reported. For example, several animals may cordon off an area of water to concentrate fish within it, and dominance hierarchies determine the order in which individuals feed (3).

Conflict with humans presents perhaps the greatest threat to the Nile crocodile. As large and potentially dangerous predators, people are often, understandably, intolerant of crocodiles, and deliberate destruction of nests and killing of adults is common (6). Crocodiles may also come into conflict with fishermen, damaging nets when trying to remove fish from them (10).

In addition, the Nile crocodile is popular for its skins, used to make high-quality leather, and hide hunting between the 1940s and 1960s resulted in large population declines throughout its range (3) (6).

Although now relatively secure and abundant in southern and eastern Africa, Nile crocodile populations may be greatly depleted in the central and western parts of its range (6), due partly to heavy hunting in the past, and partly to ongoing habitat loss. Other threats to the species include, for example, invasion of its habitat by non-native plants, such as Chromolaena odorata, which may be shading and crowding out Nile crocodile nesting sites in Greater St Lucia Wetland Park in South Africa, cooling eggs and possibly leading to an all-female population (11).

Ironically, exploitation for skins and meat has proved to be a valuable tool in Nile crocodile conservation, providing an incentive for people to protect the species and its habitat (6) (10). Although listed on Appendix I of the Convention on International Trade in Endangered Species (CITES), meaning most international trade in this species is banned, it has been downgraded to Appendix II in a number of countries (5), allowing a certain level of commercial utilisation and trade, mainly in the form of ranching (3) (6). In this system, eggs or hatchlings are taken from the wild and reared in captivity (6). As well as providing an incentive to protect the wild population, this practice may even help boost Nile crocodile numbers as it improves the survival rate of the young, a proportion of which may be returned to the wild (10). These sustainable-use initiatives are also thought to be responsible for the lack of illegal trade in this species (3).

As a result of successful management in many areas, the Nile crocodile is still widely distributed and generally has healthy populations (3) (6). It also occurs in a number of protected areas, such as Lake Turkana National Park in Kenya (12) and iSamangaliso Wetland Park in South Africa, where the population of Nile crocodiles is one of the largest in Africa (13).

However, there is still a need for population surveys and ecological studies in many central and western African countries, as well as development and implementation of management programmes in these areas, and educational programmes to teach local people about the importance of this impressive reptile while reducing the incidence of human-crocodile conflict (3) (6).

For more information on the Nile crocodile and on crocodilian conservation and research, visit:

Authenticated (13/07/09) by Adam Britton, Crocodilian.com.
http://crocodilian.com/

  1. IUCN Red List (December, 2008)
    http://www.iucnredlist.org/
  2. Alden, P.C., Estes, R.D., Schlitter, D. and McBride, B. (1996) Collins Guide to African Wildlife. HarperCollins Publishers, London.
  3. Crocodilian Species List: Crocodylus niloticus (December, 2008)
    http://www.flmnh.ufl.edu/cnhc/csp_cnil.htm
  4. Modha, M.L. (1967) The ecology of the Nile crocodile (Crocodylus niloticus Laurenti) on Central Island, Lake Rudolf. African Journal of Ecology, 5(1): 74-95.
  5. CITES (December, 2008)
    http://www.cites.org/
  6. Ross, R.P. (1998) Crocodiles: Status Survey and Conservation Action Plan. Second Edition. IUCN/SSC Crocodile Specialist Group, IUCN, Gland, Switzerland and Cambridge, UK. Available at:
    http://www.iucncsg.org/ph1/modules/Publications/action_plan1998/plan1998a.htm
  7. IUCN Species Survival Commission - Crocodile Specialist Group (December, 2008)
    http://iucncsg.org/
  8. Hutton, J.M. (1987) Incubation temperatures, sex ratios and sex determination in a population of Nile crocodiles (Crocodylus niloticus). Journal of Zoology, 211(1): 143-155.
  9. Kofron, C.P. (1990) The reproductive cycle of the Nile crocodile (Crocodylus niloticus). Journal of Zoology, 221(3): 477-488.
  10. Revol, B. (1995) Crocodile farming and conservation, the example of Zimbabwe. Biodiversity and Conservation, 4:299-305.
  11. Leslie, A.J. and Spotila, J.R. (2001) Alien plant threatens Nile crocodile (Crocodylus niloticus) breeding in Lake St. Lucia, South Africa. Biological Conservation, 98: 347-355.
  12. UNEP-WCMC: Lake Turkana National Parks, Kenya (December, 2008)
    http://www.unep-wcmc.org/medialibrary/2011/06/28/408be0a0/Lake%20Turkana.pdf
  13. UNEP-WCMC: iSamangaliso Wetland Park, KwaZulu-Natal, South Africa (December, 2008)
    http://www.unep-wcmc.org/medialibrary/2011/06/29/0efed969/iSimangaliso.pdf