Nile crocodile
Nile crocodile | |
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At Le Bonheur Crocodile Farm near Stellenbosch, South Africa | |
Scientific classification | |
Domain: | Eukaryota |
Kingdom: | Animalia |
Phylum: | Chordata |
Class: | Reptilia |
Clade: | Archosauromorpha |
Clade: | Archosauriformes |
Order: | Crocodilia |
Family: | Crocodylidae |
Genus: | Crocodylus |
Species: | C. niloticus
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Binomial name | |
Crocodylus niloticus Laurenti , 1768 | |
Approximate range of the Nile crocodile sensu lato (true area of occupancy considerably smaller and western African populations now considered to belong to the West African crocodile)[2]
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Synonyms | |
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The Nile crocodile (Crocodylus niloticus) is a large
Nile crocodiles are opportunistic
Nile crocodiles are relatively social.
The Nile crocodile is one of the most dangerous species of crocodile and is responsible for hundreds of human deaths every year.[15] It is common and is not endangered, despite some regional declines or extirpations in Maghreb.
Etymology and naming
The
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).[19][20]
In a study of the
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).[23][26][27][28][29][30] The fossil species C. checchiai from the Miocene in Kenya was about the same size as the extant African Nile crocodiles and shared similar physical characteristics to this specific species.[26][27][31]
At one time, the fossil species
Below is a
Crocodylinae |
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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.[18] The flanks, which are yellowish-green in colour, have dark patches arranged in oblique stripes in highly variable patterns. Some variation occurs relative to environment; specimens from swift-flowing waters tend to be lighter in colour than those dwelling in murkier lakes or swamps, which provides camouflage that suits their environment, an example of clinal variation. Nile crocodiles have green eyes.[9] The colouration also helps to camouflage them; juveniles are grey, multicoloured, or brown, with dark cross-bands on the tail and body.[32] The underbelly of young crocodiles is yellowish green. As they mature, Nile crocodiles become darker and the cross-bands fade, especially those on the upper-body. A similar tendency in coloration change during maturation has been noted in most crocodile species.[19][33]
Most morphological attributes of Nile crocodiles are typical of crocodilians as a whole. Like all crocodilians, for example, the Nile crocodile is a
Skull and head morphology
The mouths of Nile crocodiles are filled with 64 to 68 sharply pointed, cone-shaped
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.[9][42] 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.[8]
Biting force
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.[43] 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).[44] 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.[45][46]
Size
The Nile crocodile is the largest crocodilian in Africa, and is generally considered the second-largest crocodilian after the saltwater crocodile.[9] 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.[10][32][33] Alexander and Marais (2007) give the typical mature size as 2.8 to 3.5 m (9 ft 2 in to 11 ft 6 in); Garrick and Lang (1977) put it at from 3.0 to 4.5 m (9 ft 10 in to 14 ft 9 in).[47][8][12] 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).[10] 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).[48] Similarly, adult crocodiles from Kruger National Park reportedly average 3.65 m (12 ft 0 in) in length.[9] 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 more robust and ranks second to the saltwater crocodile in total average body mass among living crocodilians, and is considered to be the second-largest extant reptile.[8][48][9][33] 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).[8] Another large male measuring 5.8 m (19 ft 0 in) in total length (Cott 1961) was among the largest Nile crocodiles ever recorded. It was estimated to weigh 1,082 kg (2,385 lb).[49]
Size and sexual dimorphism
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.[32][50] 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 750 kg (330 to 1,650 lb).[10][48][51][52][53] 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).[8][9][54] Large mature males can reach 1,000 kg (2,200 lb) or more in weight.[55] 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).[10][48][32][56]
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 5 m (16 ft 5 in) in length and weighs 800 kg (1,800 lb). In 2007, at the Katavi National Park, Brady Barr captured a specimen measuring 5.36 m (17 ft 7 in) in total length (with a considerable portion of its tail tip missing). The weight of this specimen was estimated to be 838 kg (1,847 lb), making it one of the largest crocodiles ever to be captured and released alive.[49] 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.[10][9] 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).[10][8][57] One of the largest known specimens from South Africa, caught by J.G Kuhlmann in Venda, which was 5.5 m (18 ft 1 in) long weighed 905.7 kg (1,997 lb).[58] On the other hand, another individual measuring 5.87 m (19 ft 3 in) in length was estimated to weigh between 770–820 kg (1,700–1,800 lb).[59] 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).[10][48][60][61] 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.[8][62]
Nile crocodiles from cooler climates, like the southern tip of Africa, may be smaller, reaching maximum lengths of only 4 m (13 ft 1 in). A crocodile population from
Distribution and habitat
The Nile crocodile is presently the most common crocodilian in Africa. Among crocodilians today, only the saltwater crocodile occurs over a broader geographic area,
Isolated populations also exist in
The species was previously thought to extend in range into the whole of
Nile crocodiles may be able to tolerate an extremely broad range of habitat types, including small brackish streams, fast-flowing rivers,
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.[81] 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.[82] It is unknown how many Nile crocodiles are currently at large in Florida.[83][84] The animals likely were either brought there to be released or are escapees.[85]
Behaviour
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.[10][86] 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.[9] However, mouth-gaping (while essential to thermoregulation) may also serve as a threat display to other crocodiles. For example, some specimens have been observed mouth-gaping at night, when overheating is not a risk.[14] In Lake Turkana, crocodiles rarely bask at all through the day, unlike crocodiles from most other areas, for unknown reasons, usually sitting motionless partially exposed at the surface in shallows, with no apparent ill effects from the lack of basking on land.[57]
In South Africa, Nile crocodiles are more easily observed in winter because of the extensive amount of time they spend basking at this time of year. More time is spent in water on overcast, rainy, or misty days.
Nile crocodiles usually dive for only a few minutes at a time, but can swim under water up to 30 minutes if threatened. If they remain fully inactive, they can hold their breath for up to 2 hours (which, as aforementioned, is due to the high levels of lactic acid in their blood).
Nile crocodiles have been widely known to have
Hunting and diet
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.
The Nile crocodile mostly hunts within the confines of waterways, attacking aquatic prey or terrestrial animals when they come to the water to drink or to cross.
Subadult and smaller adult Nile crocodiles use their bodies and tails to herd groups of fish toward a bank, and eat them with quick sideways jerks of their heads. Some crocodiles of the species may habitually use their tails to sweep terrestrial prey off balance, sometimes forcing the prey specimen into the water, where it can be more easily drowned.[9] They also cooperate, blocking migrating fish by forming a semicircle across the river.[32] The most dominant crocodile eats first. Their ability to lie concealed with most of their bodies under water, combined with their speed over short distances, makes them effective opportunistic hunters of larger prey. They grab such prey in their powerful jaws, drag it into the water, and hold it underneath until it drowns. They also scavenge or steal kills from other predators, such as lions and leopards (Panthera pardus).[10] Groups of Nile crocodiles may travel hundreds of meters from a waterway to feast on a carcass.[32] They also feed on dead hippopotamuses (Hippopotamus amphibius) as a group (sometimes including three or four dozen crocodiles), tolerating each other. Much of the food from crocodile stomachs may come from scavenging carrion, and the crocodiles could be viewed as performing a similar function at times as do vultures or hyenas on land.[9] Once their prey is dead, they rip off and swallow chunks of flesh. When groups are sharing a kill, they use each other for leverage, biting down hard and then twisting their bodies to tear off large pieces of meat in a "death roll". They may also get the necessary leverage by lodging their prey under branches or stones, before rolling and ripping.[9]
The Nile crocodile possesses unique predation behavior characterized by the ability of preying both within water, where it is best adapted, and out of it, which often results in unpredictable attacks on almost any other animal up to twice its size. Most hunting on land is done at night by lying in ambush near forest trails or roadsides, up to 50 m (170 ft) from the water's edge.
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.[17][98] 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.[100] 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.[10] Intimidation displays may also resolve these conflicts. However, when size differences are prominent, the predators may prey on each other.
Reproduction
On average, sexual maturity is obtained from 12 to 16 years of age.[50] For males, the onset of sexual maturity occurs when they are about 3.3 m (10 ft 10 in) long and mass of 155 kg (342 lb), being fairly consistent.[101] 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 2.2 to 3 m (7 ft 3 in to 9 ft 10 in) in length.[10] Similarly, a wide range of studies from southern Africa found that the average length for females at the onset of sexual maturity was 2.33 m (7 ft 8 in).[102] 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 1.5 m (4 ft 11 in) although it is questionable whether such clutches would bear healthy hatchlings.[57][103]
According to Bourquin (2008), the average breeding female in southern Africa is between 3 and 3.6 m (9 ft 10 in and 11 ft 10 in).[102] Earlier studies support that breeding is often inconsistent in females less than 3 m (9 ft 10 in) and clutch size is smaller, a female at 2.75 m (9 ft 0 in) reportedly never lays more than 35 eggs, while a female measuring 3.64 m (11 ft 11 in) can expect a clutch of up to 95 eggs.[10][9] In "stunted" newly mature females from Lake Turkana measuring 1.83 m (6 ft 0 in), the average clutch size was only 15.[48][57] Graham and Beard (1968) hypothesized that, while females do continue to grow as do males throughout life, that past a certain age and size that females much over 3.2 m (10 ft 6 in) in length in Lake Turkana no longer breed (supported by the physiology of the females examined here); however, subsequent studies in Botswana and South Africa have found evidence of nesting females at least 4.1 m (13 ft 5 in) in length.[57][102][104] In the Olifants River in South Africa, rainfall influenced the size of nesting females as only larger females (greater than 3 m (9 ft 10 in)) nested during the driest years. Breeding females along the Olifants were overall larger than those in Zimbabwe.[104] Most females nest only every two to three years while mature males may breed every year.[14][102]
During the
Females lay their
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 25 yd × 22 yd (75 ft × 66 ft), in another 24 in an area of 26 yd × 24 yd (78 ft × 72 ft). 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.[10][109][110][111] 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.[9] Females will not leave nest site even if rocks are thrown at her back and several authors note her trance-like state while standing near nest, similar to that of crocodiles in aestivation but not like any other stage in their life-cycle. In such a trance, some mother Nile crocodiles may show no discernable reaction even if pelted with stones.[10][9] At other times, the female will fiercely attack anything approaching their eggs, sometimes joined by another crocodile which may be the sire of the young.[9][112] 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.[14][57] Despite the attentive care of both parents, the nests are often raided by humans and monitor lizards or other animals while she is temporarily absent.[113]
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.[10][105] Nile crocodiles have temperature-dependent sex determination (TSD), which means the sex of their hatchlings is determined not by genetics as is the case in mammals and birds, but by the average temperature during the middle third of their incubation period. If the temperature inside the nest is below 31.7 °C (89.1 °F), or above 34.5 °C (94.1 °F), the offspring will be female. Males can only be born if the temperature is within that narrow range.[114] The hatchlings start to make a high-pitched chirping noise before hatching, which is the signal for the mother to rip open the nest.[115][116] 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.[10][57] The mother crocodile may pick up the eggs in her mouth, and roll them between their tongue and the upper palate to help crack the shell and release her offspring. Once the eggs hatch, the female may lead the hatchlings to water, or even carry them there in her mouth, as female American alligators have been observed doing.[10][9]
Hatchling Nile crocodiles are between 280 and 300 mm (11 and 12 in) long at first and weigh around 70 g (2.5 oz). The hatchlings grow approximately that length each year for the first several years.
Natural mortality of young Nile crocodiles
An estimated 10% of eggs will survive to hatch and a mere 1% of young that hatch will successfully reach adulthood.
Predators of Nile crocodiles eggs have ranged from insects such as the
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.
An estimated 250,000 to 500,000 individuals occur in the wild today. The
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
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.[9] The Nile crocodile also consumes dead animals that would otherwise pollute the waters.
Attacks on humans
Much of the hunting of and general animosity toward Nile crocodiles stems from their reputation as a man-eater, which is not entirely unjustified.[135] 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.[8][19][136][137] 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.[8][15] 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.[15]
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.[9][138] 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.[139] 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.[139][140][141] Other wild animals responsible for more annual human mortalities either attack humans in self-defense, as do venomous snakes,[142] or are deadly only as vectors of disease or infection, such as snails,[143] rats[144] and mosquitos.[145]
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
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.[10][9][57] 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".[9][57]
Notes
- ^ Except the populations of Botswana, Egypt, Ethiopia, Kenya, Madagascar, Malawi, Mozambique, Namibia, South Africa, Uganda, Tanzania, Zambia and Zimbabwe which are included in CITES Appendix II.
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External links
- Media related to Crocodylus niloticus at Wikimedia Commons
- "Nile crocodile" at the Encyclopedia of Life
- Multimedia information from National Geographic Kids site