Nile crocodile by 89k6m84A

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									Nile crocodile
Nile crocodile




Conservation status




Least Concern (IUCN 2.3)[1]
Scientific classification
Kingdom:            Animalia
Phylum:             Chordata
Class:              Reptilia
(unranked):         Archosauria
Order:              Crocodylia
Family:             Crocodylidae
Subfamily:          Crocodylinae
Genus:              Crocodylus
Species:            C. niloticus
Binomial name
Crocodylus                       niloticus
(Laurenti, 1768)
Nile crocodile range

The Nile crocodile or Common crocodile (Crocodylus niloticus) is an African crocodile which
is common in Somalia, Ethiopia, Uganda, Kenya, Egypt, Tanzania, Zambia and Zimbabwe.


Contents
       1 Distribution and habitat
       2 Biology and appearance
       3 Size
       4 Diet and eating behavior
       5 Mating and breeding
       6 Environmental status
       7 In myth
       8 In literature
       9 Etymology
       10 See also
       11 References
       12 External links



Distribution and habitat
In antiquity, Nile crocodiles occurred in the Nile delta and the Zarqa River (Jordan), and they are
recorded by Herodotus to have inhabited Lake Moeris. They are thought to have become extinct
in the Seychelles in the early 19th century. It is known from fossil remains that they once
inhabited Lake Edward.[2] The Nile crocodile's current range of distribution extends from the
Senegal River, Lake Chad, Wadai and the Sudan to the Cunene and the Okavango Delta. In
Madagascar, crocodiles occur in the western and southern parts from Sembirano to Port
Dauphin. They have occasionally been spotted in Zanzibar and the Comoros.[2] Until recently,
many permanent waters in the Sahara still housed relict populations.[3]

In West Africa, Nile crocodiles are found most frequently in coastal lagoons, estuaries, and in the
rivers bordering the equatorial forest belt. In East Africa, they are found mostly in rivers, lakes,
marshes, and dams. They have been known to enter the sea in some areas, with one specimen
having been seen 11 km off St Lucia Bay in 1917. In Madagascar, they have adapted to living in
caves.[2]

Biology and appearance




View of a Nile crocodile from the side

Nile crocodiles have a dark bronze colouration above, with black spots on the back and a dirty
purple on the belly. The flanks, which are yellowish green in colour, have dark patches arranged
in oblique stripes. There is some variation relative to environment; specimens from swift flowing
waters tend to be lighter in colour than those dwelling in lakes or swamps. They have green
eyes.[2]

Like all crocodiles, they are quadrupeds with four short, splayed legs; long, powerful tails; a
scaly hide with rows of ossified scutes running down their back and tail; and powerful jaws.
They have nictitating membranes to protect their eyes and have lachrymal glands, and can
cleanse their eyes with tears.

Nostrils, eyes, and ears are situated on the tops of their head, so the rest of the body can remain
concealed underwater. Their coloration also helps them hide: Juveniles are grey, multicoloured,
or brown; with darker cross-bands on their tail and body. As they mature they become darker and
the cross-bands fade, especially those on the body. The underbelly is yellowish, and makes high-
quality leather.

They normally crawl along on their bellies, but they can also "high walk" with their trunks raised
above the ground. Smaller specimens can gallop, and even larger crocodiles are capable of
surprising bursts of speeds, briefly reaching up to 12 to 14 km/h (7.5 to 8.5 mi/h). They can swim
much faster by moving their body and tail in a sinuous fashion, and they can sustain this form of
movement much longer at about 30 to 35 km/h (18 to 22 mi/h).

They have a three-chambered heart which is often mistaken as four-chambered due to an
elongated cardiac septum, which is physiologically similar to the four chambered heart of a bird,
which is especially efficient at oxygenating their blood. They normally dive for only a couple of
minutes, but will stay underwater for up to 30 minutes if threatened, and if they remain inactive
they can hold their breath for up to 2 hours. They have an ectothermic metabolism, so they can
survive a long time between meals — though when they do eat, they can eat up to half their body
weight at a time.

They have a rich vocal range, and good hearing. Their skin has a number of poorly understood
integumentary sense organs (ISOs), that may react to changes in water pressure.

The bite force exerted by an adult Nile crocodile has been shown by Dr. Brady Barr to measure
5,000 lbf (22 kN). However, the muscles responsible for opening the mouth are exceptionally
weak, allowing a man to easily hold them shut with a small amount of force.[4] Their mouths are
filled with a total of 64 to 68 cone-shaped teeth. On each side of the mouth, there are 5 teeth in
the front of the upper jaw (the premaxilla), 13 or 14 in the rest of the upper jaw (the maxilla),
and 14 or 15 on either side of the lower jaw (the mandible). Hatchlings quickly lose a hardened
piece of skin on the top of their mouth called the egg tooth, which they use to break through their
egg's shell at birth.

Outside water crocodiles can meet concurrence with other dominant Savanna predators, notably
felines such as lions and leopards. Occasionally, both will hunt and prey on each other,
depending on size, if regular food becomes scarce.[5][6]

Size




Healthy mid-sized adult

The Nile crocodile is the largest crocodilian in Africa and is sometimes regarded as the second
largest crocodilian after the saltwater crocodile. The male crocodile usually measure from 11.5 to
16 feet long (3.5 to 5 meters), but very old, mature ones can grow to 18 ft (5.5 m) or more.[7]
Like all crocodiles they are sexually dimorphic, with the males up to 30% larger than the
females, though the difference is even more in some species, like the saltwater crocodile. Mature
female Nile crocodiles measure 8 to 13 ft (2.4 to 4.0 m)[8] Typical Nile crocodile weight is
225 kg (500 lb), though 730 kg (1,600 lb) is possible.[9] The largest accurately measured male
was shot near Mwanza, Tanzania and measured 6.45 m (21.2 ft) and weighed approximately
1,090 kg (2,400 lb).[10]
Average Nile crocodile size (green) along with size of Gustave (grey) compared to a human

7-metre (23 ft) specimens and larger have been reported, but since gross overestimation of size is
common these reports are suspect. The largest living specimen is purported to be a man-eater
from Burundi named Gustave; he is believed to be more than 20 ft (6.1 m) long. Such giants are
rare today; before the heavy hunting of the 1940s and 1950s, a larger population base and more
extensive wetland habitats meant more giants.

There is some evidence that Nile crocodiles from cooler climates like the southern tip of Africa
are smaller, and may reach lengths of only 4 m (13 ft). Dwarf Nile crocodiles also exist in Mali
and in the Sahara desert, which reach only 2 to 3 m (6.5 to 10 ft) in length. Their reduced size is
probably the result of the less than ideal environmental conditions, not genetics.[11]

Diet and eating behavior
The Nile crocodile possesses unique predation behavior characterized by the ability of preying
both within its natural habitat (where it is the apex predator) and out of its normal range, which
often results in unpredicted attacks on almost any other animal equal or smaller in size. In the
water, where the only possible threat the Nile crocodile can meet are species of its own kind, it 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.[12] Out of water, however, the
Nile crocodile can only rely on its limbs (as it gallops on solid ground) to chase the prey.[13] Most
hunting on land is done at night by lying in ambush near forest trails or roadsides, up to 50 m
(170 feet) from the water edge.[14]




A drawing depicting the mythical relationship between plovers and crocodiles. No reliable
observations exist of this purported symbiosis.
Young hatchlings generally feed on smaller prey, preferring insects and small aquatic
invertebrates before taking on fish, amphibians and small reptiles. Juveniles and subadults take a
wider variety of prey with additions such as birds and small to mid-sized mammals. Throughout
its life, both young and mature crocodiles can feed on fish and other small vertebrates on
separate occasions, when large food is absent, as a side diet. Adults are apex predators and prey
upon various birds, reptiles and mammals in addition to prey consumed also by the young and
juvenile specimens. Among the mammals, diet consists of gazelles, antelope, waterbuck,
sitatunga, lechwe, wildebeest, zebra, warthog, young hippos, giraffe,[15] Cape buffalos,[15] young
elephants, cheetah, and even big cats[16] such as leopards and lions. When given the chance, they
are known to prey upon domestic animals like chickens, goats, sheep and cattle. Nile crocodiles
also prey on humans frequently, far more often than other crocodilian species (although in parts
of the Philippines and New Guinea saltwater crocodile attacks can also be common). This is due
to the extensive use of Nile crocodile habitat by people who are unable to afford proper crocodile
safety equipment. Although not common, crocodiles can also hunt in packs of five or more
individuals while in the water, which can lead to the capture of much larger prey such as
hippopotamus and even the Black Rhinoceros.[2]

Adult Nile crocodiles use their bodies and tail to herd groups of fish toward a bank, and eat them
with quick sideways jerks of their heads. They also cooperate, blocking migrating fish by
forming a semicircle across the river. The most dominant crocodile eats first. Their ability to lie
concealed with most of their body underwater, 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 will also scavenge kills,
although they avoid rotting meat. Groups of Nile crocodiles may travel hundreds of meters from
a waterway to feast on a carcass. Once their prey is dead, they rip off and swallow chunks of
flesh. When groups of Nile crocodiles are sharing a kill, they use each other for leverage, biting
down hard and then twisting their body to tear off large pieces of meat. This is called the death
roll. They may also get the necessary leverage by lodging their prey under branches or stones,
before rolling and ripping.

Herodotus claimed that Nile crocodiles have a symbiotic relationship with certain birds like the
Egyptian plover, which enter the crocodile's mouth and pick leeches that have been feeding on
the crocodile's blood, but there is no evidence of this interaction actually occurring in any
crocodile species, and it is most likely mythical or allegorical fiction.[17]

Mating and breeding




A float of crocodiles at Disney's Animal Kingdom
For males, the onset of sexual maturity occurs when they are about 3 metres (10 ft) long while
for females, it occurs when they reach 2 to 2.5 m (6.5 to 8 ft) in length. This takes about 10 years
for either sex, under normal conditions.

During the mating season, males attract females by bellowing, slapping their snouts in the water,
blowing water out of their noses, and making a variety of other noises. The larger males of a
population tend to be more successful. Once a female has been attracted, the pair warble and rub
the underside of their jaws together. Females lay their eggs about two months after mating.

Nesting is in November or December, which is the dry season in the north of Africa, and the
rainy season in the south. Preferred nesting locations are sandy shores, dry stream beds, or
riverbanks. The female then digs a hole a couple of meters from the bank and up to 500 mm
(20 in) deep, and lays between 25 and 80 eggs. The number of eggs varies between different
populations, but averages around 50. Multiple females may nest close together.

The eggs resemble hen eggs, but have a much thinner shell.

Unlike most other crocodilians, female Nile crocodiles will bury their eggs in sand rather than
incubate them in rotting vegetation.[2] After burying the eggs, the female then guards them for
the 3 month incubation period. The father-to-be will often stay nearby, and both parents will
fiercely attack anything that approaches their eggs. The impending mother will only leave the
nest if she needs to cool off (thermoregulation), by taking a quick dip or seeking out a patch of
shade. Despite the attentive care of both parents, the nests are often raided by humans, monitor
lizards, and other animals while the mother is temporarily absent.

The hatchlings start to make a high-pitched chirping noise before hatching, which is the signal
for the mother to rip open the nest. Both the mother and father may pick up the eggs in their
mouths, and roll them between their tongue and the upper palate of their mouth to help crack the
shell, and release their offspring. Once they are hatched, the female may lead the hatchlings to
water, or even carry them there, in her mouth.




Nile crocodile eggs

Nile crocodiles have Temperature-dependent sex determination (TSD), which means the sex of
their hatchlings is determined not by genetics, 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 5-degree range.

Hatchlings are about 300 mm (12 in) long at birth, and grow that much each year. 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
to protect them, either in their mouth or in her gular or throat pouch, to keep the babies safe. The
mother will sometimes carry her young on her back to avoid them getting eaten by turtles or
water snakes. At the end of the two years, the hatchlings will be about 1.2 m (4 ft) long, and will
naturally depart the nest area, avoiding the territories of older and larger crocodiles.

Crocodile longevity is not well established, but larger species like the Nile crocodile live longer,
and may have an average life span of 70–100 years.

Environmental status
From the 1940s to the 1960s, the Nile crocodile was hunted, primarily for high-quality leather,
though also for meat and purported curative properties. The population was severely depleted,
and the species faced extinction. National laws, and international trade regulations have resulted
in a resurgence in many areas, and the species as a whole is no longer threatened with extinction.
Crocodile 'protection programs' are artificial environments where crocodiles exist safely and
without the threat of extermination from hunters.

There are an estimated 250,000 to 500,000 individuals in the wild. The Nile crocodile is also
widely distributed, with strong, documented populations in many countries in east and southern
Africa, including Somalia, Ethiopia, Kenya, Zambia and Zimbabwe. Successful sustainable-yield
programs focused on ranching crocodiles for their skins have been successfully implemented in
this area, and even countries with quotas are moving toward ranching. In 1993, 80,000 Nile
crocodile skins were produced, the majority from ranches in Zimbabwe and South Africa.

The situation is more grim in central and west Africa, which make up about two-thirds of the
Nile crocodile's habitat. The crocodile population in this area is much more sparse, and has not
been adequately surveyed. While the natural population of Nile crocodiles 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. Additional factors
are a loss of wetland habitats, and hunting in the 1970s. Additional ecological surveys and
establishing management programs are necessary to resolve this.

The Nile crocodile is the top predator in its environment, and is responsible for checking the
population of species like the barbel catfish, a predator that can overeat fish populations that
other species, like birds, depend on. The Nile crocodile also consumes dead animals that would
otherwise pollute the waters. The primary threat to Nile crocodiles, in turn, are humans. While
illegal poaching is no longer a problem, they are threatened by pollution, hunting, and accidental
entanglement in fishing nets.
Much of the hunting stems from their reputation as a man-eater, which is not entirely unjustified.
Unlike other "man-eating" crocodiles, like the Saltwater Crocodile, the Nile crocodile lives in
close proximity to human populations, so contact is more frequent. While there are no solid
numbers, the Nile crocodile probably kills a couple of hundred people a year, which is more than
all the other crocodiles combined.[18] Some estimates put the number of annual victims in the
thousands.[10]

The Conservation Status of the Nile crocodile under the 1996 World Conservation Union
(IUCN) Red List is "Lower Risk" (Lrlc). The Convention on International Trade in Endangered
Species of Wild Fauna and Flora (CITES) lists the Nile crocodile under Appendix I (threatened
with extinction) in most of its range; and under Appendix II (not threatened, but trade must be
controlled) in the remainder, which either allows ranching or sets an annual quota of skins taken
from the wild.

In myth




Sobek

The people of Ancient Egypt worshiped Sobek, a crocodile-god associated with fertility,
protection, and the power of the pharaoh.[19] They had an ambivalent relationship with Sobek, as
they did (and do) with the Nile crocodile; sometimes they hunted crocodiles and reviled Sobek,
and sometimes they saw him as a protector and source of pharonic power.
Sobek was depicted as a crocodile, as a mummified crocodile, or as a man with the head of a
crocodile. The center of his worship was in the Middle Kingdom city of Arsinoe in the Faiyum
Oasis (now Al Fayyum), known as "Crocodilopolis" by the Greeks. Another major temple to
Sobek is in Kom-Ombo, and other temples were scattered across the country.

According to Herodotus in the 5th century BC, some Egyptians kept crocodiles as pampered
pets. In Sobek's temple in Arsinoe, a crocodile was kept in the pool of the temple, where it was
fed, covered with jewelry, and worshipped. When the crocodiles died, they were embalmed,
mummified, placed in sarcophagi, and then buried in a sacred tomb. Many mummified
crocodiles and even crocodile eggs have been found in Egyptian tombs.

Spells were used to appease crocodiles in Ancient Egypt, and even in modern times Nubian
fishermen stuff and mount crocodiles over their doorsteps to ward against evil.

In literature
Some propose the Bible's Leviathan was a Nile crocodile.[citation needed] Like the Leviathan, the
Nile crocodile is aquatic, scaly, and possesses fierce teeth. Job 41:18 states that Leviathan's eyes
"are like the eyelids of the morning".

Etymology
The binomial name Crocodylus niloticus is derived from the Greek kroko ("pebble"), deilos
("worm", or "man"), 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, Garwe in Shona,
Ngwenya in Ndebele, Ngwena in Venda, Kwena in Sotho and Tswana.

								
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