The Nile Crocodile (Crocodylus niloticus) is an African crocodile which is common in Somalia, Ethiopia, Kenya, and Zambia.
In antiquity, Nile crocodiles occurred in the Nile delta and the Zarqa River, 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. 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. In West Africa, Nile crocodiles occur 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 Santa Lucia Bay in 1917. In Madagascar, they have adapted to living in caves.
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. Their eyes are green. 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. They have a four-chambered heart, like 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 Doctor 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.The Nile crocodile is an opportunistic apex predator capable of taking almost any animal that is within attacking range. They start life very small however, therefore the diet of hatchlings consists of smaller prey. Hatchlings eat insects and small aquatic invertebrates, and quickly graduate to amphibians, reptiles, and birds. But even as an adult, a significant portion of a Nile crocodile's diet is fish and other small vertebrates. However, adult crocodiles prefer to consume larger prey to conserve energy. In the absence of large prey, they gradually have to move onto smaller prey. Nile crocodiles have a very broad diet and can potentially eat nearly any animal that comes to take a drink at the edge of the water. The most frequently recorded mammalian prey taken by Nile crocodiles are waterbuck, sitatunga, lechwe, wildebeest, zebra, warthog, goats, sheep and cattle. Larger herbivores such as Cape buffalo and giraffes are also preyed upon. In addition, there is at least one record of a group of crocodiles killing a female Black Rhinoceros in the Tana river. Predators like hyenas, leopards and other crocodiles, including their own species have been recorded to be eaten. The African Big Cats have occasionally been observed preying on young crocodiles and in contrast large adult crocodiles have been observed attacking both leopards and lions when food is scarce. Generally large predators avoid other large predators given the "high risk" of injury (although crocodiles are much better equipped to deal with infection and limb loss than other predators, with many crocodiles living to old age with missing arms, legs or portions of the jaw.) Adults are the apex predators of their environment and are not preyed on.
A Spur-winged Plover picking the teeth of a Nile crocodile 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. Nile crocodiles are reputed to have a symbiotic relationship with certain birds like the spur-winged plover. According to reports, the crocodile opens its mouth widely, and then the bird picks leeches that have been feeding on the crocodile's blood. This has proven to be a symbiotic relationship.