Nile crocodile

Details of the skull from a juvenile Nile crocodile

The mouths of Nile crocodiles are filled with 64 to 68 sharply pointed, cone-shaped teeth (about a dozen less than alligators have). For most of a crocodile's life, broken teeth can be replaced. On each side of the mouth, five teeth are in the front of the upper jaw (premaxilla), 13 or 14 are in the rest of the upper jaw (maxilla), and 14 or 15 are on either side of the lower jaw (mandible). The enlarged fourth lower tooth fits into the notch on the upper jaw and is visible when the jaws are closed, as is the case with all true crocodiles.[8][29] Hatchlings quickly lose a hardened piece of skin on the top of their mouths called the egg tooth, which they use to break through their eggshells at hatching. Among crocodilians, the Nile crocodile possesses a relatively long snout, which is about 1.6 to 2.0 times as long as broad at the level of the front corners of the eyes.[35] As is the saltwater crocodile, the Nile crocodile is considered a species with medium-width snout relative to other extant crocodilian species.[36]

In a search for the largest crocodilian skulls in museums, the largest verifiable Nile crocodile skulls found were several housed in Arba Minch, Ethiopia, sourced from nearby Lake Chamo, which apparently included several specimens with a skull length more than 65 cm (26 in), with the largest one being 68.6 cm (27.0 in) in length with a mandibular length of 87 cm (34 in). Nile crocodiles with skulls this size are likely to measure in the range of 5.4 to 5.6 m (17 ft 9 in to 18 ft 4 in), which is also the length of the animals according to the museum where they were found. However, larger skulls may exist, as this study largely focused on crocodilians from Asia.[7][37] The detached head of an exceptionally large Nile crocodile (killed in 1968 and measuring 5.87 m (19 ft 3 in) in length) was found to have weighed 166 kg (366 lb), including the large tendons used to shut the jaw.[6]

The bite force exerted by an adult Nile crocodile has been shown by Brady Barr to measure 22 kN (5,000 lbf). However, the muscles responsible for opening the mouth are exceptionally weak, allowing a person to easily hold them shut, and even larger crocodiles can be brought under control by the use of duct tape to bind the jaws together.[38] The broadest snouted modern crocodilians are alligators and larger caimans. For example, a 3.9 m (12 ft 10 in) black caiman (Melanosuchus niger) was found to have a notably broader and heavier skull than that of a Nile crocodile measuring 4.8 m (15 ft 9 in).[39] However, despite their robust skulls, alligators and caimans appear to be proportionately equal in biting force to true crocodiles, as the muscular tendons used to shut the jaws are similar in proportional size. Only the gharial (Gavialis gangeticus) (and perhaps some of the few very thin-snouted crocodilians) is likely to have noticeably diminished bite force compared to other living species due to its exceptionally narrow, fragile snout. More or less, the size of the tendons used to impart bite force increases with body size and the larger the crocodilian gets, the stronger its bite is likely to be. Therefore, a male saltwater crocodile, which had attained a length around 4.59 m (15 ft 1 in), was found to have the most powerful biting force ever tested in a lab setting for any type of animal.[40][41]

Healthy subadult

The Nile crocodile is the largest crocodilian in Africa, and is generally considered the second-largest crocodilian after the saltwater crocodile.[7] Typical size has been reported to be as much as 4.5 to 5.5 m (14 ft 9 in to 18 ft 1 in), but this is excessive for actual average size per most studies and represents the upper limit of sizes attained by the largest animals in a majority of populations.[3][27][28] According to the Guinness Book of World Records, the typical mature size is between 3.4 and 3.7 m (11 ft 2 in and 12 ft 2 in), while Alexander and Marais (2007) state it is 2.8 to 3.5 m (9 ft 2 in to 11 ft 6 in) and Garrick and Lang (1977) claim from 3.0 to 4.5 m (9 ft 10 in to 14 ft 9 in).[4][6][9] According to Cott (1961), the average length and weight of Nile crocodiles from Uganda and Zambia in breeding maturity was 3.16 m (10 ft 4 in) and 137.5 kg (303 lb).[3] Per Graham (1968), the average length and weight of a large sample of adult crocodiles from Lake Turkana (formerly known as Lake Rudolf), Kenya was 3.66 m (12 ft 0 in) and body mass of 201.6 kg (444 lb).[42] Similarly, adult crocodiles from Kruger National Park reportedly average 3.65 m (12 ft 0 in) in length.[7] In comparison, the saltwater crocodile and gharial reportedly both average around 4 m (13 ft 1 in), so are about 30 cm (12 in) longer on average and the false gharial (Tomistoma schlegelii) may average about 3.75 m (12 ft 4 in), so may be slightly longer, as well. However, compared to the narrow-snouted, streamlined gharial and false gharial, the Nile crocodile is rather more robust and ranks second to the saltwater crocodile in total average body mass among living crocodilians and third among all living reptiles - the massive leatherback turtle (Dermochelys coriacea) has a mean body mass slightly less than that of an average mature male saltwater crocodiles.[6][42][7][28] The largest accurately measured male, shot near Mwanza, Tanzania, measured 6.45 m (21 ft 2 in) and weighed about 1,043–1,089 kg (2,300–2,400 lb).[6]

Groupings of crocodiles like this can include crocodiles of various sizes, but seldom of less than 2 m (6 ft 7 in), lest a cannibalistic large specimen launch an attack.

Like all crocodiles, they are sexually dimorphic, with the males up to 30% larger than the females, though the difference is considerably less compared to some species, like the saltwater crocodile. Male Nile crocodiles are about 30 to 50 cm (12 to 20 in) longer on average at sexual maturity and grow more so than females after becoming sexually mature, especially expanding in bulk after exceeding 4 m (13 ft 1 in) in length.[27][43] Adult male Nile crocodiles usually range in length from 3.3 to 5.0 m (10 ft 10 in to 16 ft 5 in) long; at these lengths, an average sized male may weigh from 150 to 700 kg (330 to 1,540 lb).[3][42][44][45][46] In Limpopo, South Africa, males reportedly average 527 kg (1,162 lb).[5] Very old, mature ones can grow to 5.5 m (18 ft 1 in) or more in length (all specimens over 5.5 m (18 ft 1 in) from 1900 onward are cataloged later).[6][7][47] Mature female Nile crocodiles typically measure 2.2 to 3.8 m (7 ft 3 in to 12 ft 6 in), at which lengths the average female specimen would weigh 40 to 250 kg (88 to 551 lb).[3][42][27][48]

The bulk and mass of individual crocodiles can be fairly variable, some animals being relatively slender, while others being very robust; females are often bulkier than males of a similar length.[3][7] As an example of the body mass increase undergone by mature crocodiles, one of the larger crocodiles handled firsthand by Cott (1961) was 4.4 m (14 ft 5 in) and weighed 414.5 kg (914 lb), while the largest specimen measured by Graham and Beard (1973) was 4.8 m (15 ft 9 in) and weighed more than 680 kg (1,500 lb).[3][6][49] In attempts to parse the mean male and female lengths across the species, the mean adult length was estimated to be reportedly 4 m (13 ft 1 in) in males, at which males would average about 280 kg (620 lb) in weight, while that of the female is 3.05 m (10 ft 0 in), at which females would average about 116 kg (256 lb).[3][42][50][51] This gives the Nile crocodile somewhat of a size advantage over the next largest non-marine predator on the African continent, the lion (Panthera leo), which averages 188 kg (414 lb) in males and 124 kg (273 lb) in females, and attains a maximum known weight of 313 kg (690 lb), far less than that of large male crocodiles.[6][52]

Evidence exists of Nile crocodiles from cooler climates, like the southern tip of Africa, being smaller, and may reach maximum lengths of only 4 m (13 ft 1 in). A smaller population from Mali, the Sahara Desert, and elsewhere in West Africa reaches only 2 to 3 m (6 ft 7 in to 9 ft 10 in) in length,[53] but it is now largely recognized as a separate species, the West African crocodile.[19]

Nile crocodiles are an invasive species in North America, and several specimens have been recently captured in South Florida, though no signs that the population is reproducing in the wild have been found.[69] Genetic studies of Nile crocodiles captured in the wild in Florida have revealed that the specimens are all closely related to each other, suggesting a single source of the introduction. This source remains unclear, as their genetics do not match samples collected from captives at various zoos and theme parks in Florida. When compared to Nile crocodiles from their native Africa, the Florida wild specimens are most closely related to South African Nile crocodiles.[70] It is unknown how many Nile crocodiles are currently at large in Florida.[71][72] The animals likely were either brought there to be released, or are escapees.[73]

The type and size of the prey depends mostly on the size of the crocodile.[51] The diet of young crocodiles is made up largely of insects and other invertebrates, since this is the only prey the same animals can easily take. More than 100 species and genera of insects were identified among the food of crocodiles of this age. Of the insects taken there, beetles made up 58% of the diet, including Hydrophilus and Cybister. giant water bugs but also crickets and dragonflies. Arachnids such as Dolomedes water spiders are taken, but always secondarily to insects in Uganda and Zambia.[3][85]

Crabs are also largely taken by crocodiles under 1.5 m (4 ft 11 in), especially the genus Potamonautes, with different species being the primary crustacean food in different areas. Mollusks may occasionally be taken by young crocodiles (they are taken in larger numbers later in life in parts of Uganda and Zambia).[3] In the Okavango Delta, Botswana, the diet was similar but young crocodiles ate a broader range of insects and invertebrates, with beetles taken in similar numbers to other, similar prey, both aquatic and terrestrial. In Botswana, arachnids were more often found in young crocodiles than in Uganda and Zambia.[85] In Zimbabwe, the dietary composition was broadly similar to that in other areas.[51] However, in the Ugandan portion of Lake Victoria, true bugs and dragonflies both seem to outnumber beetles notably and up to a length of 1 to 2 m (3 ft 3 in to 6 ft 7 in) crocodiles had stomach contents that were made up 70–75% of insects.[86][87]

After Nile crocodiles reach 2 m (6 ft 7 in), the significance of most invertebrates in the diet decreases precipitously.[3][85] An exception to this is in Uganda and Zambia, where subadults and adults of even large sizes, up to 3.84 m (12 ft 7 in), may eat very large numbers of snails. Nearly 70% of the crocodiles examined by Cott (1961) had some remains of snails inside their stomachs. Predation on amuplariid water snails was especially heavy in Bangweulu Swamp, Lake Mweru Wantipa, and the Kafue Flats, where mollusks representing 89.1, 87, and 84.7% of all prey in these locations, respectively. Gastropoda (4126 records per Cott) were taken much more than Lamellibranchiata (six records). Notable favorites include Pila ovata, which lives just under water on rocky surfaces (mainly found in crocodiles from Uganda) and Lanistes ovum, which is found submerged among water plants and on detritus (mainly from stomachs in Zambia).[3]

Subadult with tilapia as its prey

During the time from when they are roughly 1.5 to 2.2 m (4 ft 11 in to 7 ft 3 in) long (roughly 5 to 9 years old), Nile crocodiles seem to have the broadest diet of any age range. They take more or less much the same small prey as smaller crocodiles, including insects and arachnids, but also take many small to medium-sized vertebrates and quickly become capable taking down prey up to their own weight. Fish become especially significant around this age and size. However, Cott (1961) found that the only size range where fish were numerically dominant over other types of food was from 2 to 3.05 m (6 ft 7 in to 10 ft 0 in). This size range consists of subadult males and a mixture of subadult and adult females.[3] In Lake Turkana, fish were the only food in the stomachs of 45.4% of the crocodiles that did not have empty stomachs, in total 87.8% of the crocodiles that did not have empty stomachs there had fish in their stomachs. Graham (1968) noted that throughout East Africa, crocodile diets are driven by the regional availability of prey. The arid land surrounding Lake Turkana is a relatively barren region for diverse or numerous prey other than fish, so fish are an exceptionally important food source to crocodiles there.[42][49] In Lake Kyoga and Lake Kwana, 73.1% of the crocodiles that did not have empty stomachs had fish in their stomachs.[88] At Lake St. Lucia in South Africa, many Nile crocodile congregate to feed on striped mullet (Mugil cephalus) as they make their seaward migration for spawning. Here, the crocodiles may line up in dozens across narrow straits of the estuary to effectively force the mullet into easy striking distance, with no observed in-fighting among these crocodile feeding congregations. At this time of plenty (before irrigation operations by humans led St. Lucia to have dangerously high saline levels), a 2.5 m (8 ft 2 in) crocodile could expect to eat 1.1 kg (2.4 lb) of mullet daily, an exceptionally large daily amount for a crocodile.[89]

Larger fish, like catfish and freshwater bass, are preferred by adults more than 2.2 m (7 ft 3 in) in length. Particularly small fish are likely to be eaten only in case of sudden encounter, mostly in shallow, dry-season ponds where not much effort is needed to catch the small, agile prey.[14] Most observed fishing by crocodiles takes place in waters less than 1.5 m (4 ft 11 in) deep and fish are often caught when they swim into contact with the crocodile's head, even literally right into the reptile's mouth.[42] Across much of their range, they take any fish they encounter, but largish and relatively sluggish mesopredator fish such as lungfish and Barbus carp seem to be most widely reported. Many other genera are taken widely and relatively regularly, including Tilapia (which was the most significant prey genus in Lake Turkana), Clarias, Haplochromis, and Mormyrus.[3][42][90] In Uganda and Zambia, lungfish comprised nearly two-thirds of the piscivorian diet for crocodiles.[3] Similarly, in Lake Baringo, the lungfish is the crocodile's main prey and the crocodile is the lungfish's primary predator.[91] In the Okavango Delta, the African pikes (Hepsetus spp.) were the leading prey group for subadults, comprising more than a fourth of the diet.[92] Extremely large fish, such as Nile perch (Lates niloticus), goliath tigerfish (Hydrocynus goliath), and even sharks, are taken on occasion, in addition to big catfish, such as Bagrus spp. and Clarias gariepinus, which are preyed upon quite regularly in areas where they are common. In the Zambezi River and Lake St. Lucia, Nile crocodiles have been known to prey on bull sharks (Carcharhinus leucas) and sand tiger sharks (Carcharias taurus).[93][94][95] The largest fishes attacked in such cases may potentially weigh more than 45 kg (99 lb).[96][97]

When capturing large fish, they often drag the fish onto shore and swing their heads around to smash the fish onto the ground until it is dead or incapacitated. More modestly sized fish are generally swallowed whole.[42] The Nile crocodile has a reputation as a voracious and destructive feeder on freshwater fish, many of which are essential to the livelihoods of local fisherman and the industry of sport fishing. However, this is very much an unearned reputation. As cold-blooded creatures, Nile crocodiles need to eat far less compared to an equivalent-weighted warm-blooded animal. The crocodile of 2 to 3.05 m (6 ft 7 in to 10 ft 0 in) consumes an average 286 g (10.1 oz) of fish per day. In comparison, piscivorous water birds from Africa eat far more per day despite being a fraction of the body size of a crocodile, for example a cormorant eats up to 1.4 kg (3.1 lb) per day (about 70% of its own body weight), while a pelican consumes up to 3.1 kg (6.8 lb) per day (about 35% of its own weight).[3][7] The taking of commercially important fish, such as Tilapia, has been mentioned as a source of conflict between humans and crocodiles, and used as justification for crocodile-culling operations; however, even a primarily piscivorous crocodile needs relatively so little fish that it cannot deplete fish populations on its own without other (often anthropogenic) influences.[98] Additionally, crocodiles readily take dead or dying fish given the opportunity, thus are likely to incidentally improve the health of some fish species’ populations as this lessens their exposure to diseases and infection.[7]

Captive adult Nile crocodiles feeding

Frogs are regionally significant prey for small, young crocodiles in many regions, mainly those in the 0.5 to 1.5 m (1 ft 8 in to 4 ft 11 in) size range. The main amphibian prey species from Uganda and Zambia was the African common toad (Amietophrynus regularis) while in Botswana, the main amphibian prey was the reed frog (Hyperolius viridiflavus).[3][85] Even the largest frog in the world, the goliath frog (Conraua goliath), has reportedly been preyed on by young Nile crocodiles.[99]

In general, reptiles become relatively common only in the diet in larger juvenile specimens and subadults. Large reptiles, or armoured reptiles such as turtles, were almost negligible in crocodiles under 2.5 m (8 ft 2 in) and most common in the stomachs of crocodiles over 3.5 m (11 ft 6 in) in length from Uganda and Zambia. Small species of reptiles are largely ignored as prey at this size. Freshwater turtles are often the most frequently recorded reptilian prey, unsurprisingly perhaps because most other reptiles other than a small handful of Lycodonomorphus water snakes are more terrestrial than water-based.[3]

In a study, the serrated hinged terrapin (Pelusios sinuatus) (also sometimes referred to as the "water tortoise") was more commonly reported in the stomach contents of adult crocodiles from Kruger National Park than any single mammal species.[100] Other turtle species commonly recorded among Nile crocodile prey include the Speke's hinge-back tortoise (Kinixys spekii) and East African black mud turtle (Pelusios subniger). Beyond their ready availability and respectable size, turtles are favored by big crocodiles due to their slowness, which allows the cumbersome crocodiles to capture them more easily than swifter vertebrates.[7][101][102] While adults have a sufficient bite force to crush turtle shells, younger crocodiles sometimes are overly ambitious, and will choke to death attempting to swallow whole large river turtles.[18] A variety of snakes has been preyed on from relatively small, innocuous species such as the common egg-eating snake (Dasypeltis scabra) to the largest African snakes species, the African rock python (Python sebae), which can exceed 6.1 m (20 ft 0 in) in length and weigh over 91 kg (201 lb). Venomous species, including the puff adder (Bitis arietans), the forest cobra (Naja melanoleuca), and the black mamba (Dendroaspis polylepis) have been recorded as Nile crocodile prey.[3][7] The only frequently recorded lizard prey is the large Nile monitor (Varanus niloticus), although this mesopredator may be eaten fairly regularly, as they often share similar habitat preferences, whenever a crocodile is able to ambush the stealthy monitor, which is more agile on land than the bulkier crocodile.[3][7]

Pelicans have little to fear from crocodiles on land, but are quite vulnerable while swimming to crocodiles lurking under water.

Numerous birds, including storks, small wading birds, waterfowl, eagles, and even small, swift-flying birds, may be snatched. As a whole, birds are quite secondary prey, rarely comprising more than 10–15% of crocodiles' diets, although are taken fairly evenly across all crocodile size ranges, excluding juveniles less than 1 m (3 ft 3 in).[3][7][27] Birds most often taken are African darters (Anhinga rufa) and reed (Microcarbo africanus) and white-breasted cormorants (Phalacrocorax lucidus), followed by various waterfowl, including most breeding geese and ducks in Africa. Slow-swimming pelicans are also frequently vulnerable to crocodiles.[103] Nile crocodiles apparently frequently station themselves underneath breeding colonies of darters and cormorants and presumably snatch up fledgling birds as they drop to the water before they can competently escape the saurian, as has been recorded with several other crocodilians.[3][7]

Wading birds, even large and relatively slow-moving types such as the goliath heron (Ardea goliath), tend to be highly cautious in avoiding deep water in crocodile-occupied wetlands, whereas cormorants and waterfowl forage over deeper water and are easier for crocodiles to ambush, with Egyptian geese (Alopochen aegyptiaca) and spur-winged geese (Plectropterus gambensis) recorded as being taken largely while flightless due to molting their flight feathers.[104][105][106][107][108] On the contrary, several records exist of them capturing wading birds. Guggisberg (1972) saw multiple cases of predation on marabou storks (Leptoptilos crumenifer) and around Lake Turkana several may frequent heronries to pick off fledglings.[42][7] In one case, a crocodile was filmed capturing a striated heron (Butorides striata) in mid-flight.[109] Ospreys (Pandion haliaetus) are known to be grabbed while they dive for fish[110] as are possibly African fish eagles (Haliaeetus vocifer), while crowned eagles (Stephanoaetus coronatus) have reportedly been ambushed on land at carrion.[7][111] Crocodiles are occasionally successful in grabbing passerines such as weaver birds, including the abundant red-billed quelea (Quelea quelea), and swallows, having been observed to breach the water and in a matter of seconds sweep off a branch full of birds with remarkable success.[7][112][113][114] Larger land birds, such as bustards, guineafowl, ground hornbills (Bucorvus spp.) and ostriches (Struthio camelus), may be taken when they come to water to drink, but like most birds, are seldom harassed and a minor part of the diet.[7][115]

Determining the percentage of any specific food item in a crocodile's diet is difficult because their defecation in water makes scat analysis impossible, and capturing individual animals to analyze their stomach contents is painstaking. In addition, as an animal that feeds rarely, sometimes only a few times in a year, even the individual stomach content examinations sometimes prove to be unsuccessful. However, as crocodiles grow, relying solely on small and agile food items such as fish becomes difficult, this causes a shift in the diet as the animal matures, for energy conservation purposes, as in other predators.[3][42] Nonetheless, starting around 1.5 m (4 ft 11 in), they can become capable mammalian hunters and their ability to overpower a wide range of mammals increases along with their size. Crocodiles less than 3 m (9 ft 10 in) may take a variety of medium–sized mammals up to equal their own mass, including various monkeys, duikers,[116] rodents, hares, pangolins,[3] bats, dik-dik, suni (Neotragus moschatus),[117] oribi (Ourebia ourebi)[118] and other small ungulates up to the size of a Thomson's gazelle (Eudorcas thomsonii).[49]

Rodents and shrews may enter the diet of juvenile crocodiles, i.e. 1.0 to 1.5 m (3 ft 3 in to 4 ft 11 in), and become commonplace in subadult and small adult crocodiles. Species recorded include the Natal multimammate mouse (Mastomys natalensis), African marsh rat (Dasymys incomtus), common rufous-nosed rat (Oenomys hypoxanthus), and savanna swamp shrew (Crocidura longipes).[3][85] In many areas, the cane rats are a particular favorite mammalian food for crocodiles, particularly the relatively large greater cane rat (Thryonomys swinderianus). In Uganda and Zambia, the latter species are the leading overall mammalian prey type for crocodiles and one Kenyan crocodile of 2.7 m (8 ft 10 in) in length had 40 greater cane rats in its stomach.[3][7][119] Cape porcupines (Hystrix africaeaustralis) are known to have been preyed on several times in Kruger National Park, their quills apparently being an insufficient defense against the tough jaws and digestive systems of crocodiles.[84][100] Small carnivores are readily taken opportunistically, including both African clawless otters (Aonyx capensis)[120] and spotted-necked otters (Hydrictis maculicollis),[7] as well as water mongoose (Atilax paludinosus),[3] African wildcats (Felis silvestris lybica)[3] and servals (Leptailurus serval).[121]

Adult Nile crocodiles, i.e. at least 3.05 m (10 ft 0 in), are apex predators. While adults can and will consume nearly all types of prey consumed by the younger specimens, as adult crocodiles gain bulk, they lose much of the necessary maneuverability to capture agile prey such as fish and are not likely to meet their dietary needs by consuming small prey and may expel unnecessary amounts of energy, so take them secondarily to larger prey.[7][100] Primates of various sizes may be taken by subadult or adult crocodiles. In some areas, some number of baboons is taken, such as in Okavango Delta, where chacma baboons (Papio ursinus) are eaten and Uganda, where olive baboons (Papio anubis) are taken.[122][123] No records of them hunting apes (other than humans) have been made, but based on a strong reluctance to cross waters with crocodiles and a violent reaction to the visual stimuli of crocodiles, chimpanzees (Pan troglodytes) and gorillas (Gorilla beringei) are thought to consider Nile crocodiles a serious threat.[124] Few details are known about the dietary habits of Nile crocodiles living in Madagascar, although they are considered potential predators of several lemur species.[125][126] Other nonungulate prey known to be attacked by Nile crocodiles includes aardvarks (Orycteropus afer)[127] and African manatees (Trichechus senegalensis).[128]

Wildebeest crossing the Mara River, attacked by crocodiles

Among the mammals, the bulk of the prey for adults is antelopes. In particular, the genus Kobus is often among the most vulnerable because it forages primarily in wetland areas and seeks to evade more prolific mammalian predators (such as hyenas, lions, etc.) by traveling along waterways.[7][100] In some cases in Kruger National Park, antelope have been driven into water while being pursued by packs of African wild dogs (Lycaon pictus), which hunt by endurance, engaging prey in a grueling chase until it is exhausted (a very successful hunting style), only to be killed by opportunistic crocodiles.[14] While not as extensively aquatic as the genus Kobus, the reedbucks and the impala (Aepyceros melampus) have both shown a partiality for grasslands adjoining wetlands and riparian zones, so are also very commonly recorded prey items. In Kruger National Park, over the course of 22 years of discontinuous observation, 60% of the large-game kills observed as perpetrated by crocodiles consisted of impala, while more than 15% of observed kills were made up of waterbuck (Kobus ellipsiprymnus), the largest of the genus Kobus at more than 200 kg (440 lb) in weight.[84][100] Elsewhere, the waterbuck appears to be the most significant mammalian prey for large adult crocodiles, such as in Uganda and Zambia (although due to more sporadic general ungulate populations in those countries, ungulates are less common as prey than in some other countries), as well as in Hluhluwe–iMfolozi Park, South Africa.[3][129] Other antelopes recorded as prey including gazelles,[84] bushbuck (Tragelaphus scriptus),[100] sitatunga (Tragelaphus spekii),[7] kudu (Tragelaphus strepsiceros),[130] steenbok (Raphicerus campestris),[131] eland (Taurotragus oryx),[84] gemsbok (Oryx gazella),[132] sable (Hippotragus niger) and roan antelopes (Hippotragus equinus),[132] up to a half dozen types of duiker,[117] topi (Damaliscus lunatus),[133] hartebeest (Alcelaphus buselaphus)[7] and both species of wildebeest (Connochaetes sp.).[134]

Other ungulates are taken by Nile crocodile more or less opportunistically. These may include Grévy's (Equus grevyi)[135] and plains zebras (Equus quagga),[136] pygmy hippopotamus (Choeropsis liberiensis),[137] warthogs (Phacochoerus africanus),[7] bushpigs (Potamochoerus larvatus)[100] and red river hogs (Potamochoerus porcus).[3] In Maasai Mara, Tanzania, large crocodiles congregate at river crossings utilized by migrating herds of Burchell's zebras and blue wildebeests (Connochaetes taurinus), picking off hundreds of these large ungulates annually.[138] All domesticated ungulates and pet animals will on occasion be hunted by Nile crocodiles, up to the size of dromedary camels (Camelus dromedarius)[139] and cattle (Bos taurus)[65] In Tanzania, up to 54 head of cattle may be lost to crocodiles annually, increasing the human-crocodile conflict level. Goats (Capra aegagrus hircus), donkeys (Equus africanus asinus) and dogs (Canis lupus familiaris) may also rank among the most regularly recorded domesticated animals to be taken by Nile crocodiles.[7][140]

Particularly large adults, on occasion, take on even larger prey, such as giraffe (Giraffa camelopardalis),[100][141] Cape buffalo (Syncerus caffer),[100][141] and young African bush elephants (Loxodonta africana).[142][143] Even heavier prey, such as black rhinoceros (Diceros bicornis), have been killed by crocodiles. In one case in the Tana River of Kenya, as observed by Max Fleishmann (communicated via letter to Theodore Roosevelt), a crocodile was able to bring down one of these huge herbivores by the help of muddy bank terrain, the adult female rhino's poor decision to enter deeper water rather than retreat to land and finally having been joined in drowning the animal by one to two other crocodiles.[7][144] An additional case of predation on an adult black rhino was reportedly observed in northern Zambia.[7] A bull giraffe that lost his footing on a river bank in Kruger National Park was seen to be killed by a large crocodile, while in another case there, a healthy bull buffalo was seen to be overpowered and killed by an average-sized adult male crocodile measuring 4.25 m (13 ft 11 in) after a massive struggle, an incident less commonly seen at this size.[42][100] Since crocodiles are solitary hunters, the Nile crocodile is the only predator in Africa known to attack full-grown buffaloes alone, compared to the preferred pride attack method of lions.[145]

Although crocodiles occasionally prey on hippopotamus calves, even large adult crocodiles rarely attack them because of the aggressive defense by mother hippos and the close protection of the herd, which pose a serious threat. Hippopotamus calves have been observed to at times act brazenly around crocodiles, foraging without apparent concern and even bumping into the reptiles.[7] However, some large crocodiles have been recorded as predators of subadult hippos; anecdotally, the infamous giant crocodile Gustave was reported to have been seen killing adult female hippos.[84][100][146] A 5 m (16 ft 5 in) specimen from Zambia was found to have eaten a "half-grown hippo".[3] At the no-longer-existent Ripon Falls in Uganda, one adult male hippopotamus was seen to be badly injured in a mating battle with a rival bull hippo, and was then subsequently attacked by several crocodiles, causing it to retreat to a reedbed. When the male hippo returned to the water, it was drowned and killed by the group of crocodiles amid "a truly terrifying commotion".[7] However, other than rare instances, adults of megafauna species such as hippopotamuses, rhinoceroses, and elephants are not regular prey and are not typically attacked, with the exception of giraffes, since their anatomy makes them vulnerable to attack while taking a drink.

Nile crocodiles on occasion prey on big cats including lions and leopards.[100][116][134][147] However, in order to save energy, crocodiles do not prefer such agile animals, as most attacks will end before they can strike. Thus they usually attack agile prey in the absence of regular prey items.[3][7] Other large carnivores that dwell in Africa near the top of the food chain can also on occasion fall prey to crocodiles. Such predators that can find themselves victim to crocodiles include hyenas (3 out of 4 species reported as prey for Nile crocodiles, only the desert-dwelling brown (Hyaena brunnea) being excluded),[116][148] African wild dogs, jackals,[84][100] and cheetahs (Acinonyx jubatus).[49]

In the Nile crocodile as well as in at least 13 other species of crocodilian, a variety of fruit (mostly fleshy) has been found in stomach content. While these are probably sometimes used as gastroliths, they are likely often ingested for their nutritional value. Based on these findings, it has also been suggested that crocodiles may act as seed dispersers.[149]

Living in the rich biosphere of Africa south of the Sahara, the Nile crocodile may come into contact with multiple other large predators. Its place in the ecosystems it inhabits is largely unique, as it is the only large tetrapod carnivore that spends the majority of its life in water and hunting prey associated with aquatic zones. Large mammalian predators in Africa are often social animals and obligated to feed almost exclusively on terrestrial zones.[14][100] The Nile crocodile is a strong example of an apex predator. Outside water, crocodiles can meet competition from other dominant savannah predators, notably big cats, which in Africa are represented by lions, cheetahs, and leopards. In general, big cats and crocodiles have a relationship of mutual avoidance. Occasionally, if regular food becomes scarce, both lions and the crocodile will steal kills on land from each other and, depending on size, will be dominant over one another. Both species may be attracted to carrion, and may occasionally fight over both kills or carrion.[150] Most conflicts over food occur near the water and can literally lead to a tug-of-war over a carcass that can end either way, although seldom is there any serious fighting or bloodshed between the large carnivores.[3] Intimidation displays may also resolve these conflicts. However, when size differences are prominent, the predators may prey on each other. 2 cases of Leopards preying on Crocodiles were reported.[151]

An estimated 10% of eggs will survive to hatch and a mere 1% of young that hatch will successfully reach adulthood.[3][49] The full range of causes for mortality of young Nile crocodiles is not well understood, as very young and small Nile crocodiles or well-concealed nests are only sporadically observed. Unseasonable flooding (during nesting which corresponds with the regional dry season) is not uncommon and has probably destroyed several nests, although statistical likelihood of such an event is not known.[7][49] The only aspect of mortality in this age range that is well studied is predation and this is most likely the primary cause of death while the saurians are still diminutive.[169] The single most virulent predator of nests is almost certainly the Nile monitor. This predator can destroy about 50% of studied Nile crocodile eggs on its own, often being successful (as are other nest predators) in light of the trance-like state that the mother crocodile enters while brooding or taking advantage of moments where she is distracted or needs to leave the nest. In comparison, perenties (Varanus giganteus) (the Australian ecological equivalent of the Nile monitor) succeeds in depredating about 90% of freshwater crocodile (Crocodylus johnsoni) eggs and about 25% of saltwater crocodile nests.[169] Mammalian predators can take nearly as heavy of a toll, especially large mongooses such the Egyptian mongoose (Herpestes ichneumon) in the north and the water mongoose in the south of crocodile's range. Opportunistic mammals who attack Nile crocodile nests have included wild pigs, medium-sized wild cats and baboon troops. Like Nile monitors, mammalian predators probably locate crocodile nests by scent as the padded-down mound is easy to miss visually.[14][169] Marabou storks sometimes follow monitors to pirate crocodile eggs for themselves to consume, although can also dig out nests on their own with their massive, awl-like bills if they can visually discern the nest mound.[7][169]

Predators of Nile crocodiles eggs have ranged from insects such as the red flour beetle (Tribolium castaneum) to predators as large and formidable as spotted hyenas (Crocuta crocuta).[169] Unsurprisingly, once exposed to the elements as hatchlings, the young, small Nile crocodiles are even more vulnerable. Most of the predators of eggs also opportunistically eat young crocodiles, including monitors and marabous, plus almost all co-existing raptorial birds, including vultures, eagles, and large owls and buzzards. Many "large waders" are virulent predators of crocodile hatchlings, from dainty little egrets (Egretta garzetta) and compact hamerkops (Scopus umbretta) to towering saddle-billed storks (Ephippiorhynchus senegalensis), goliath herons and shoebills (Balaeniceps rex). Larger corvids and some non-wading water birds (i.e. pelicans) can also take some young Nile crocodiles. Mammalian carnivores take many hatchlings as well as large turtles and snakes, large predatory freshwater fish, such as the African tigerfish, the introduced largemouth bass, and possibly bull sharks, when they enter river systems. When crocodile nests are dug out and the young placed in water by the mother, in areas such as Royal Natal National Park predators can essentially enter a feeding frenzy.[169][170][171][172] It may take a few years before predation is no longer a major cause of mortality for young crocodiles. African fish eagles can take crocodile hatchlings up to a few months of age and honey badgers can prey on yearlings. Once they reach their juvenile stage, very large African rock pythons and big cats remain as the only predatory threat to young crocodiles.[6][7][173] Perhaps no predator is more deadly to young Nile crocodiles than larger crocodiles of their own species, as, like most crocodilians, they are cannibalistic. This species may be particularly dangerous to their own kind considering the aggressive disposition they tend to bear.[7][76][174] While the mother crocodile will react aggressively toward potential predators and has been recorded chasing and occasionally catching and killing such interlopers into her range, due to the sheer number of animals who feed on baby crocodiles and the large number of hatchlings, she is more often unsuccessful at deflecting such predators.[3][7][169]

Makeshift barrier in Uganda to lessen the risk of crocodile attacks

Much of the hunting of and general animosity toward Nile crocodiles stems from their reputation as a man-eater, which is not entirely unjustified.[186] Despite most attacks going unreported, the Nile crocodile along with the saltwater crocodile is estimated to kill hundreds (possibly thousands) of people each year, which is more than all other crocodilian species combined.[6][15][187][188] While these species are much more aggressive toward people than other living crocodilians (as is statistically supported by estimated numbers of crocodile attacks), Nile crocodiles are not particularly more likely to behave aggressively to humans or regard humans as potential prey than saltwater crocodiles. However, unlike other "man-eating" crocodile species, including the saltwater crocodile, the Nile crocodile lives in close proximity to human populations through most of its range, so contact is more frequent. This combined with the species’ large size renders a higher risk of attack.[6][11] Crocodiles as small as 2.1 m (6 ft 11 in) are capable of overpowering and successfully preying on small apes and hominids, presumably including children and smaller adult humans, but a majority of fatal attacks on humans are by crocodiles reportedly exceeding 3 m (9 ft 10 in) in length.[11]

In studies preceding the slaughter of crocodiles for the leather trade, when there were believed to be many more Nile crocodiles, a roughly estimated 1,000 human fatalities per annum by Nile crocodiles were posited with a roughly equal number of aborted attacks.[7][189] A more contemporary study claimed the number of attacks by Nile crocodiles per year as 275 to 745, of which 63% are fatal, as opposed to an estimated 30 attacks per year by saltwater crocodiles, of which 50% are fatal. With the Nile crocodile and the saltwater crocodile, the mean size of crocodiles involved in non-fatal attacks was about 3 m (9 ft 10 in) as opposed to a reported range of 2.5–5 m (8 ft 2 in–16 ft 5 in) or larger for crocodiles responsible for fatal attacks. The average estimated size of Nile crocodiles involved in fatal attacks is 3.5 m (11 ft 6 in). Since a majority of fatal attacks are believed to be predatory in nature, the Nile crocodile can be considered the most prolific predator of humans among wild animals.[190] In comparison, lions, in the years from 1990 to 2006, were responsible for an estimated one-eighth as many fatal attacks on humans in Africa as were Nile crocodiles. Although Nile crocodiles are more than a dozen times more numerous than lions in the wild, probably fewer than a quarter of living Nile crocodiles are old and large enough to pose a danger to humans.[190][191][192] Other wild animals responsible for more annual human mortalities either attack humans in self-defense, as do venomous snakes,[193] or are deadly only as vectors of disease or infection, such as snails,[194] rats[195] and mosquitos.[196]

Regional reportage from numerous areas with large crocodile populations nearby indicate, per district or large village, that crocodiles often annually claim about a dozen or more lives per year. Miscellaneous examples of areas in the last few decades with a dozen or more fatal crocodile attacks annually include Korogwe District, Tanzania, Niassa Reserve, Mozambique and the area around Lower Zambezi National Park, Zambia.[197][198] Despite historic claims that the victims of Nile crocodile attacks are usually "women and children",[6] there is no detectable trends in this regard and any human, regardless of age, gender, or size is potentially vulnerable. Incautious human behavior is the primary drive behind crocodile attacks.[11] Most fatal attacks occur when a person is standing a few feet away from water on a non-steep bank, is wading in shallow waters, actively swimming or have limbs dangling over a boat or pier. Many victims are caught while crouching and people in jobs that might require heavy usage of water including laundry workers, fisherman, game wardens and regional guides are more likely to be attacked. Many fisherman and other workers who are not poverty-stricken will go out of their way to avoid waterways known to harbor large crocodile populations.[7][49][199]

Most biologists who have engaged in months or even years of field work with Nile crocodiles, including Cott (1961), Graham and Beard (1968) and Guggisberg (1972), have found that with sufficient precautions, their own lives and the lives of their local guides were rarely, if ever, at risk in areas with many crocodiles.[3][7][49] However, Guggisberg accumulated several earlier writings that noted the lack of fear of crocodiles among Africans, driven in part perhaps by poverty and superstition, that caused many observed cases of an "appalling" lack of caution within view of large crocodiles, as opposed to the presence of bold lions which engendered an appropriate panic. Per Guggisberg, this disregard (essentially regarding the crocodile as a lowly creature and thus non-threatening to humans) may account for the seemingly higher frequency of deadly attacks by crocodiles than by large mammalian carnivores. Most locals are well aware of how to behave in crocodile-occupied areas and some of the writings quoted by Guggisberg from the 19th and 20th century may require being taken with a "grain of salt".[7][49]