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| Subspecies: | Unknown |
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| Est. World Population: | 50000-70000 |
| CITES Status: | NOT LISTED |
| IUCN Status: | Least Concern |
| U.S. ESA Status: | NOT LISTED |
| Body Length: | |
| Tail Length: | |
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| Jumping Ability: | (Horizontal) |
| Life Span: | in the Wild |
| Life Span: | in Captivity |
| Sexual Maturity: | (Females) |
| Sexual Maturity: | (Males) |
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The first modern monograph on the ecology of a crocodilian was by Cott (1961) on Nile Crocodiles (Crocodylus niloticus). Since then, a large number of studies on C. niloticus have been published on topics such as diet, thermoregulation, reproduction, social behaviour, habitat preference, and population dynamics (Fergusson 2010), making C. niloticus one of the most biologically well-studied crocodilians.
As with all crocodilians, size among C. niloticus is sexually dimorphic with the larger males reaching total lengths of up to 6 m in exceptional cases (Fergusson 2010). The size at which females become sexually mature is variable. Cott (1961) reported the smallest sexually mature female from northern Zambia was 238 cm total length (TL) and southern Zambia 259 cm TL. Pitman shot 855 confirmed nesting C. niloticus females (1940 - 1949) and found only 2% smaller than 244 cm TL, with the smallest nesting females (n = 4) 237.7 cm TL (Cott 1961). The smallest live nesting female ever recorded by Pitman over a 15 year period (n = 1500 examined) was 219 cm TL (Cott 1961). Graham (1968) found the onset of maturity in Lake Rudolf (Turkana) crocodiles even smaller, from 180 cm onwards. The largest mature female shot by Pitman was 4.62 m (Graham 1968). Nile crocodiles lay 35-50 eggs, although this varies considerably among populations. The nesting season varies with geographic areas but can be generally described as a dry season activity in the north, tending to an early wet season activity in the south. Female C. niloticus excavate hole nests in sandy banks, up to 50 cm deep, a few meters from the water’s edge and actively guard the nest during incubation. A high percentage of eggs are still lost to predation from monitor lizards (Varanus niloticus; Combrink et al. 2016, Calverley and Downs 2017), marsh mongoose (Atilax paludinosus; Combrink et al. 2016), hyenas and humans when the females leave to thermoregulate (cooling in the water) or feed. Those eggs that do survive hatch after 75-95 days, with females opening the nest and guarding the young for 6-8 weeks after hatching (Fergusson 2010, Combrink et al. 2016).
Being a widely distributed species, C. niloticus are found in a wide variety of habitat types, including large lakes, rivers, and freshwater swamps (Fergusson 2010). In some areas, they extend into brackish water environments (Pooley 1982, Pauwels et al. 2004) and sometimes occupy highly saline water. In the St Lucia estuarine system of South Africa, two adult males were recorded with satellite telemetry utilising areas of the estuarine lake for months at time, with mean salinity levels of 51.9 ± 2.5 psu, although there were nearby freshwater seepages (Combrink 2014). Habitat utilization differs between juveniles, sub-adults and adults with juveniles entering a dispersal phase at approximately 1.2 m length (Hutton 1989). Modha (1967) described some aspects of the social behaviour, including the establishment of breeding hierarchies. Combrink et al. (2017) reported that gravid females selected winter basking/breeding areas close to nest-sites with a significantly smaller home range (0.85 ha) than non-gravid females (108.4 ha), providing further evidence of maternal commitment. The highest reported nest fidelity recorded with satellite telemetry during incubation was 99.7% over 96 days (Combrink et al. 2017). Nile crocodiles display an ontogenetic shift in diet consuming insects and small aquatic invertebrates when young moving to predominantly vertebrate prey as they become larger (Cott 1961, Wallace and Leslie 2008, Lyet et al. 2016). This can also include humans, particularly when anthropogenic activities occur within crocodile habitats (Sideleau 2016).
The Nile Crocodile is found in a wide diversity of water bodies (rivers, lakes, swamps, and coastal estuaries) in 26 countries in eastern, central and southern Africa. Populations are also reported from desert oasis pools and subterranean streams in caves. The species, in its current restricted sense, is reported from Angola, Botswana, Burundi, Cameroon, Congo, Democratic Republic of Congo, Egypt, Eritrea, Ethiopia, Equatorial Guinea, Gabon, Kenya, Madagascar, Malawi, Mozambique, Namibia, Rwanda, Somalia, South Africa, South Sudan, Sudan, Swaziland, Tanzania, Uganda, Zambia and Zimbabwe.
1. Population survey data is urgently needed for most countries to quantify regional status and determine objectively whether management activities, be they restricted to protection or involving sustainable use, are achieving their conservation goals. Such assessments and survey data provide an evidence-base for developing conservation and management programs in some nations.
2. Innovative approaches to raise awareness of the intrinsic and non-consumptive value of crocodiles and their management, as perceived by national authorities, are needed to prioritize crocodile conservation particularly in light of the value given to more charismatic species such as elephant, large primates and the big cats.
3. Study of human-crocodile conflict impacts, mitigation and “problem crocodile” management programs is central to Crocodylus niloticus conservation in most countries. Conflict between rural communities and crocodiles is the primary concern in the management of the wild crocodile population in many African countries. The problems are poorly understood for many reasons, including the lack of systematic recording of incidents and their context, with CrocBITE (2013) providing a valuable pioneering role. Technologies to reduce the probability of crocodile attacks exist (www.iucncsg.org) but are limited in scope and livelihood context. In countries such as Madagascar, where mitigation nominally involves the removal of crocodiles and the commercial use of their skins, the efficacy of the program and impact on the depleted wild populations needs to be assessed objectively.
4. Impact of anthropogenic contaminants, with particular attention to the South African population. Much of the South African population appears to be at risk from contamination, with large-scale die-offs documented in prominent conservation areas (e.g. Loskop Dam Nature Reserve and Kruger National Park) since 2005. Populations in St. Lucia may not be secure, with agriculture, industry (sugarcane) and human settlements in the catchment on the increase.
5. Further delineation between the ranges of C. niloticus and C. suchus is required to ensure the action plans are specific for each species.
Moderate priority
6. Allocation/demarcation of locally protected areas. Shacks (2006) looked at nest site habitat suitability versus available habitat in the Okavango Delta, Botswana. These data were then overlaid to produce a map with priority areas for nesting that led to the establishment of a nesting sanctuary for C. niloticus. This process could be repeated in other national contexts.
7. Facilitation of management programs for countries planning or implementing sustainable utilization. A number of African nations lack the appropriate policy environment, management capability and technical expertise to plan and/or implement use programs, added to the often complex social, economic and biological variables involved. Another tier lies in a commitment to adaptive rather than strictly prescriptive management, Population surveys, monitoring, data assessment, technique training, reporting and incentives are needed to foster and sustain these programs. Hutton (1990) outlined some priority areas that need to be addressed for the development of sustainable use programs in the African context:
a. Pre-feasibility studies (e.g. harvest potential);b. Policy and legislation to provide a management framework;
c. Feasibility studies (identification of potential production sites, evaluation and quantification of factors inherent in sustainable use programs);
d. International requirements for trade (CITES submissions, documentation and tagging of hides);
e. Population census and monitoring (technical support and training);
f. Technical support for developing ranching/farming programs; and,
g. Marketing.