Nile crocodile

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Nile crocodile
The Nile crocodile or Common crocodile (Crocodylus niloticus) is an African Crocodile which is common in Somalia, Ethiopia, Uganda, Kenya, Egypt, Tanzania, Zambia, Zimbabwe, Gabon, South Africa, Malawi, Sudan, Botswana, and Cameroon. Isolated populations also exist in Madagascar, Senegal.

Contents

Distribution and habitat

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.

Biology and appearance

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.

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.

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, multicolored, 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. 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 competition from 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.

Size

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 metres), but very old, mature ones can grow to 18 ft (5.5 m) or more. Mature female Nile crocodiles measure 8 to 13 ft (2.4 to 4.0 m)[8] Typical Nile crocodile weight is around 225 kg (500 lb), though large specimens can range up to 730 kg (1,600 lb) in mass.[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).

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, as well as adult hippos, 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. 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, Cape buffalos, young elephants, cheetah, and even big cats 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.

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.

Population

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, is 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. Some estimates put the number of annual victims in the thousands.

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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