Nile crocodile

The binomial name Crocodylus niloticus is derived from the Greek κρόκη, kroke ("pebble"), δρῖλος, drilos ("worm"), referring to its rough skin; and niloticus, meaning "from the Nile River". The Nile crocodile is called timsah al-nil in Arabic, mamba in Swahili, yaxaas in Somali, garwe in Shona, ngwenya in Ndebele, ngwena in Venda, kwena in Sotho and Tswana, and tanin ha-yeor in Hebrew. It also sometimes referred to as the African crocodile, Ethiopian crocodile, and common crocodile. ==Taxonomy==

Although no subspecies are currently formally recognized, as many as seven have been proposed, mostly due to variations in appearance and size noted in various populations throughout Africa. These have consisted of C. n. africanus (informally named the East African Nile crocodile), C. n. chamses (the West African Nile crocodile), C. n. cowiei (the South African Nile crocodile), C. n. madagascariensis (the Malagasy or Madagascar Nile crocodile, regionally also known as the croco Mada, which translates to Malagasy crocodile), C. n. niloticus (the Ethiopian Nile crocodile; this would be the nominate subspecies), C. n. pauciscutatus (the Kenyan Nile crocodile) and C. (n.) suchus (now widely considered a separate species). For example, a study on Lake Turkana in Kenya (informally this population would be placed in C. n. pauciscutatus) found that the local crocodiles have more osteoderms in their ventral surface than other known populations, and thus are of lesser value in leather trading, accounting for an exceptionally large (possibly overpopulated) local population there in the late 20th century. The separation of the two is not recognized by the IUCN as their last evaluations of the group was in 2008 and 2009, years before the primary publications supporting the distinctiveness of the West African crocodiles. ==Evolution==

Although originally thought to be the same species as the West African crocodile, genetic studies using DNA sequencing have revealed that the Nile crocodile is actually more closely related to the crocodiles of the Americas, namely the American (C. acutus), Cuban (C. rhombifer), Morelet's (C. moreletii), and Orinoco crocodiles (C. intermedius). The extant Nile crocodiles first appeared during the Late Miocene-Early Pliocene in Kenya based on fossil remains dated to approximately , and the related fossil species C. checchiai from the same strata was similar in size and shared similar physical characteristics to this specific species. At one time, the fossil species Rimasuchus lloydi was thought to be the closest relative of the Nile crocodile, but more recent research has indicated that Rimasuchus, despite its very large size (about 20–30% bigger than a Nile crocodile with a skull length estimated up to ), is more closely related to the dwarf crocodile (Osteolaemus tetraspis) among living species. Two other fossil species from Africa retained in the genus Crocodylus appear to be closely related to the Nile crocodile: C. anthropophagus from Plio-Pleistocene Tanzania and C. thorbjarnarsoni from Plio-Pleistocene Kenya. C. anthropophagus and C. thorbjarnarsoni were both somewhat larger, with projected total lengths up to . }} ==Characteristics and physiology==

Adult Nile crocodiles have a dark bronze colouration above, with faded blackish spots and stripes variably appearing across the back and a dingy off-yellow on the belly, although mud can often obscure the crocodile's actual colour. Their skin has a number of poorly understood integumentary sense organs that may react to changes in water pressure, presumably allowing them to track prey movements in the water. The Nile crocodile has fewer osteoderms on the belly, which are much more conspicuous on some of the more modestly sized crocodilians. The species, however, also has small, oval osteoderms on the sides of the body, as well as the throat. The Nile crocodile shares with all crocodilians a nictitating membrane to protect the eyes and lachrymal glands to cleanse its eyes with tears. The nostrils, eyes, and ears are situated on the top of the head, so the rest of the body can remain concealed under water. They have a four-chambered heart, although modified for their ectothermic nature due to an elongated cardiac septum, physiologically similar to the heart of a bird, which is especially efficient at oxygenating their blood. As in all crocodilians, Nile crocodiles have exceptionally high levels of lactic acid in their blood, which allows them to sit motionless in water for up to 2 hours. Levels of lactic acid as high as they are in a crocodile would kill most vertebrates. As is the saltwater crocodile, the Nile crocodile is considered a species with medium-width snout relative to other extant crocodilian species. 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 , with the largest one being in length with a mandibular length of . Nile crocodiles with skulls this size are likely to measure in the range of , 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. The detached head of an exceptionally large Nile crocodile (killed in 1968 and measuring in length) was found to have weighed , including the large tendons used to shut the jaw. The broadest snouted modern crocodilians are alligators and larger caimans. For example, a black caiman (Melanosuchus niger) was found to have a notably broader and heavier skull than that of a Nile crocodile measuring . 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 , was found to have the most powerful biting force ever tested in a lab setting for any type of animal. Size |170x170px The Nile crocodile is the largest crocodilian in Africa, and is generally considered the second-largest crocodilian after the saltwater crocodile. Alexander and Marais (2007) give the typical mature size as ; Garrick and Lang (1977) put it at from . Similarly, adult crocodiles from Kruger National Park reportedly average in length. Adult male Nile crocodiles usually range in length from long; at these lengths, an average sized male may weigh from . Very old, mature ones can grow to or more in length (all specimens over from 1900 onward are cataloged later). Large mature males can reach or more in weight. Mature female Nile crocodiles typically measure , at which lengths the average female specimen would weigh . An old male individual, named "Big Daddy", housed at Mamba Village Centre, Mombasa, Kenya, is considered to be one of the largest living Nile crocodiles in captivity. It measures in length and weighs . Another one in Burundi, "Gustave", has been estimated at long and close to ; it is believed to have killed hundreds of people. In 2007, at Katavi National Park, Brady Barr captured a specimen measuring in total length (with a considerable portion of its tail tip missing). The weight of this specimen was estimated to be , making it one of the largest crocodiles ever to be captured and released alive. 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. One of the largest known specimens from South Africa, caught by J. G. Kuhlmann in Venda, which was long weighed . In attempts to parse the mean male and female lengths across the species, the mean adult length was estimated to be reportedly in males, at which males would average about in weight, while that of the female is , at which females would average about . 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 in males and in females, and attains a maximum known weight of , far less than that of large male crocodiles. Nile crocodiles from cooler climates, like the southern tip of Africa, may be smaller, reaching maximum lengths of only . A crocodile population from Mali, the Sahara Desert, and elsewhere in West Africa reaches only in length, but it is now largely recognized as a separate species, the West African crocodile. ==Distribution and habitat==

, Zambia The Nile crocodile's current distribution extends from the regional tributaries of the Nile in Sudan and Lake Nasser in Egypt to the Cunene River in Angola, the Okavango Delta of Botswana, and the Olifants River in South Africa. It is the most common crocodilian in Africa and occurs in Somalia, Ethiopia, Uganda, Kenya, Central African Republic, the Democratic Republic of the Congo, Equatorial Guinea, Tanzania, Rwanda, Burundi, Zambia, Zimbabwe, Gabon, Malawi, Mozambique, Namibia, Sudan, South Sudan and Cameroon. In 2022, a skull of Crocodylus from Madagascar was found to be around 7,500 years old based on radiocarbon dating, suggesting that the extinction of Voay post-dates the arrival of Nile crocodiles on Madagascar. The Nile crocodile was previously thought to also occur in West and Central Africa, but these populations are now typically recognized as a distinct species, the West African (or desert) crocodile. The West African crocodile occurs throughout much of West and Central Africa, ranging east to South Sudan and Uganda where it may come into contact with the Nile crocodile. The Nile crocodile is absent from most of West and Central Africa, but range into the latter region in eastern and southern Democratic Republic of Congo, and along the Central African coastal Atlantic region north to Cameroon. Likely a level of habitat segregation occurs between the two species, but this remains to be confirmed. Nile crocodiles may be able to tolerate an extremely broad range of habitat types, including small brackish streams, fast-flowing rivers, swamps, dams, and tidal lakes and estuaries. In Madagascar, the remnant population of Nile crocodiles has adapted to living within caves. The Nile crocodile possesses salt glands like all true crocodiles and does on occasion enter coastal and even marine waters. They have been known to enter the sea in some areas, with one specimen having been recorded off St. Lucia Bay in 1917. Invasive potential Nile crocodiles have been recently captured in South Florida, though no signs that the population is reproducing in the wild have been found. 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. It is unknown how many Nile crocodiles are currently at large in Florida. The animals likely were either brought there to be released or are escapees. ==Behaviour==

of Murchison Falls National Park, Uganda Generally, Nile crocodiles are relatively inert creatures, as are most crocodilians and other large, cold-blooded creatures. More than half of the crocodiles observed by Cott (1961), if not disturbed, spent the hours from 9:00 a.m. to 4:00 p.m. continuously basking with their jaws open if conditions were sunny. If their jaws are bound together in the extreme midday heat, Nile crocodiles may easily die from overheating. Although they can remain practically motionless for hours on end, whether basking or sitting in shallows, Nile crocodiles are said to be constantly aware of their surroundings and aware of the presence of other animals. In the southern reaches of their range, as a response to dry, cool conditions that they cannot survive externally, crocodiles may dig and take refuge in tunnels and engage in aestivation. They can swim much faster, moving their bodies and tails in a sinuous fashion, and they can sustain this form of movement much longer than on land, with a maximum known swimming speed of . bird and the crocodile. Nile crocodiles have been widely known to have gastroliths in their stomachs, which are stones swallowed by animals for various purposes. Although this is clearly a deliberate behaviour for the species, the purpose is not definitively known. Gastroliths are not present in hatchlings, but increase quickly in presence within most crocodiles examined at and yet normally become extremely rare again in very large specimens, meaning that some animals may eventually expel them. Guggisberg (1972) had seen examples of birds picking scraps of meat from the teeth of basking crocodiles (without entering the mouth) and prey from soil very near basking crocodiles, so felt it was not impossible that a bold, hungry bird may occasionally nearly enter a crocodile's mouth, but not likely as a habitual behaviour. ==Hunting and diet==

in Kruger National Park, South Africa Nile crocodiles are apex predators throughout their range. In the water, this species is an agile and rapid hunter relying on both movement and pressure sensors to catch any prey unfortunate enough to present itself inside or near the waterfront. Out of water, however, the Nile crocodile can only rely on its limbs, as it gallops on solid ground, to chase prey. No matter where they attack prey, this and other crocodilians take practically all of their food by ambush, needing to grab their prey in a matter of seconds to succeed. Prey taken is often much smaller than the crocodile itself, and such prey can be overpowered and swallowed with ease. When it comes to larger prey, success depends on the crocodile's body power and weight to pull the prey item back into the water, where it is either drowned or killed by sudden thrashes of the head or by tearing it into pieces with the help of other crocodiles. Since their speed and agility on land is rather outmatched by most terrestrial animals, they must use obscuring vegetation or terrain to have a chance of succeeding during land-based hunts. Two subadult crocodiles were once seen carrying the carcass of a nyala (Tragelaphus angasii) across land in unison. Small carnivores are readily taken opportunistically, including African clawless otters (Aonyx capensis). Interspecific predatory relationships Living in the rich biosphere of Africa south of the Sahara, the Nile crocodile may come into contact with other large predators. Its place in the ecosystems it inhabits is 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 land. 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. Intimidation displays may also resolve these conflicts. However, when size differences are prominent, the predators may prey on each other. ==Reproduction==

at Disney's Animal Kingdom On average, sexual maturity is obtained from 12 to 16 years of age. On the other hand, that for females is rather more variable, and may be indicative of the health of a regional population based on size at sexual maturity. On average, according to Cott (1961), female sexual maturity occurs when they reach in length. However, stunted sexual maturity appears to occur in populations at opposite extremes, both where crocodiles are thought to be overpopulated and where they are overly reduced to heavy hunting, sometimes with females laying eggs when they measure as small as although it is questionable whether such clutches would bear healthy hatchlings. In the Olifants River in South Africa, rainfall influenced the size of nesting females as only larger females (greater than ) nested during the driest years. Breeding females along the Olifants were overall larger than those in Zimbabwe. Once a female has been attracted, the pair warble and rub the undersides of their jaws together. Compared to the tender behaviour of the female accepting the male, copulation is rather rough (even described as "rape"-like by Graham & Beard (1968)) in which the male often roars and pins the female underwater. The female may urinate sporadically on the soil to keep it moist, which prevents soil from hardening excessively. When Nile crocodiles have been entirely free from disturbance in the past, they may nest gregariously with the nest lying so close together that after hatching time the rims of craters are almost contiguous. These communal nesting sites are not known to exist today, perhaps being most recently recorded at Ntoroko peninsula, Uganda where two such sites remaining until 1952. In one area, 17 craters were found in an area of , in another 24 in an area of . Communal nesting areas also reported from Lake Victoria (up until the 1930s) and also in the 20th century at Rahad River, Lake Turkana and Malawi. The behaviour of the female Nile crocodile is considered unpredictable and may be driven by the regional extent of prior human disturbance and human persecution rather than natural variability. In some areas, the mother crocodiles will only leave the nest if she needs to cool off (thermoregulation) by taking a quick dip or seeking out a patch of shade. In other areas, the nesting female may disappear upon potential disturbance which may allow the presence of both the female and her buried nest to escape unwanted detection by predators. At a reported incubation period of about 90 days, the stage is notably shorter than that of the American alligator (110–120 days) but slightly longer than that of the mugger crocodile. The hatchlings start to make a high-pitched chirping noise before hatching, which is the signal for the mother to rip open the nest. It is thought to be either difficult or impossible for hatchlings to escape the nest burrow without assistance, as the surface may become very heavy and packed above them. The new mother will protect her offspring for up to two years, and if there are multiple nests in the same area, the mothers may form a crèche. During this time, the mothers may pick up their offspring either in their mouths or gular fold (throat pouch) to keep the babies safe. The mother will sometimes carry her young on her back to avoid natural predators of the small crocodiles, which can be surprisingly bold even with the mother around. Nile crocodiles of under two years are much more rarely observed than larger specimens, and more seldom seen than the same age young in several other types of crocodilian. Young crocodiles are shy and evasive due to the formidable array of predators that they must face in sub-Saharan Africa, spending little time sunning and moving about nocturnally whenever possible. Crocodiles two years old and younger may spend a surprising amount of time on land, as evidenced by the range of terrestrial insects found in their stomachs, and their lifestyle may resemble that of a semi-aquatic mid-sized lizard more so than the very aquatic lives of older crocodiles. 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. 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, large Southern African rock pythons and big cats remain as the only predatory threat to young crocodiles. 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 their aggressive dispositions. 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. ==Environmental status==

Conservation organizations have determined that the main threats to Nile crocodiles, in turn, are loss of habitat, pollution, hunting, and human activities such as accidental entanglement in fishing nets. the advent of the readily available firearm made it much easier to kill these potentially dangerous reptiles. However, as is the case for many large animal species whether they are protected or not, persecution and poaching have continued apace and between the 1950s and 1980s, an estimated 3 million Nile crocodiles were slaughtered by humans for the leather trade. Recovery for the species appears quite gradual and few areas have recovered to bear crocodile populations, i.e. largely insufficient to produce sustainable populations of young crocodiles, on par with times prior to the peak of leather trading. Crocodile 'protection programs' are artificial environments where crocodiles exist safely and without the threat of extermination from hunters. , Tunisia An estimated 250,000 to 500,000 individuals occur in the wild today. The IUCN Red List assesses the Nile crocodile as "Least Concern (LR/lc)". Crocodile farming is one of the few burgeoning industries in Zimbabwe. Unlike American alligator flesh, Nile crocodile meat is generally considered unappetizing although edible as tribes such as the Turkana may opportunistically feed on them. According to Graham and Beard (1968), Nile crocodile meat has an "indescribable" and unpleasant taste, greasy texture and a "repellent" smell. The conservation situation is more grim in Central and West Africa presumably for both the Nile and West African crocodiles. The crocodile population in this area is much more sparse, and has not been adequately surveyed. While the natural population in these areas may be lower due to a less-than-ideal environment and competition with sympatric slender-snouted and dwarf crocodiles, extirpation may be a serious threat in some of these areas. At some point in the 20th century, the Nile crocodile appeared to have been extirpated as a breeding species from Egypt, but has locally re-established in some areas such as the Aswan Dam. Retraction of wetlands due both to direct habitat destruction by humans and environmental factor possibly related to global warming is perhaps linked to the extinction of Nile crocodiles in the last few centuries in Syria, Israel and Tunisia. In yet another historic crocodile stronghold, the Olifants River, which flows through Kruger National Park, numerous crocodile deaths have been reported. These are officially due to unknown causes but analysis has indicated that environmental pollutants caused by humans, particularly the burgeoning coal industry, are the primary cause. Much of the contamination of crocodiles occurs when they consume fish themselves killed by pollutants. Additional ecological surveys and establishing management programs are necessary to resolve these questions. The Nile crocodile is the top predator in its environment, and is responsible for checking the population of mesopredator species, such as the barbel catfish and lungfish, that could overeat fish populations on which other species, including birds, rely. One of the fish predators seriously affected by the unchecked mesopredator fish populations (due again to crocodile declines) is humans, particularly with respect to tilapia, an important commercial fish that has declined due to excessive predation. 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. 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 creates a higher risk of attack. 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 as opposed to a reported range of or larger for crocodiles responsible for fatal attacks. The average estimated size of Nile crocodiles involved in fatal attacks is . 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. 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. Other wild animals responsible for more annual human mortalities either attack humans in self-defense, as do venomous snakes, or are deadly only as vectors of disease or infection, such as snails, rats and mosquitos. 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. Despite historic claims that the victims of Nile crocodile attacks are usually women and children, 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. 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 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 need to be taken with a "grain of salt". ==Notes==