Nile Crocodile - Crocodylus niloticus

Geographic range

Ethiopian: The Nile crocodile is found in Africa and on some islands, including Madagascar. The Nile crocodile was eradicated long ago in Palestine and Egypt and now cannot be found below the second cataract of the Nile. They are widespread throughout southern Africa but are absent in the northwest and Sahara regions as well as in the extreme southern portions of South Africa.

Physical characteristics

The Nile crocodile, like all crocodilians, is characterized by a lizardlike shape and a scaly hide (which is highly sought after by poachers). Their skin, unlike that of most reptiles, grows with them and is not shed. It ranges from drab green or brownish to a blackish tone on the dorsal side and is much lighter, and softer, on the ventral surface. There is virtually no way to distinguish the gender of a crocodile at a glance. The male has a penis, but it portrudes from a slit in the skin only during mating. Crocodiles can be distinguished from alligators by their long narrow snout and their fourth mandibular tooth, which portrudes from their lower jaw rather than fitting in to their upper jaw. The eyes and nostrils of crocodiles are situated on the top of the head so they can see and breathe while the rest of their body remains almost totally submerged. Unlike other reptiles, crocodiles have external ears that close, along with the nostrils, when they dive. Another feature that helps the crocodile survive in the water is its third eyelid, the nictating membrane. When a crocodile dives, it closes its transparent nictating membrane to keep water out of its eyes without sacrificing its vision. Crocodiles swim using their enormous, oar-like tail. Only their rear feet are webbed, and they are rarely used in movement underwater. On land, the crocodile walks on its short, seemingly weak legs. They bring their legs in close to their bodies and lift themselves high off the ground when walking. They have even been observed "galloping," as a rabbit does. They plant their front feet, bring their hind legs around the outsides of the front legs, plant them, and then lunge forward with their front legs. Nile crocodiles have been known to reach speeds of up to 29 miles per hour.

Mass: 272 to 910 kg.

Food Habits

The Nile crocodile will eat almost anything. Hatchlings eat insects and minnows and, as they grow, move on to consume crustaceans and large fish. Mature Nile crocodiles eat anything from fish and turtles, which they crack open with their powerful jaws, to larger mammals including baboons, hyenas, impalas, and wildebeest. It is not uncommon for these predators to kill and devour large and surprising prey such as young hippopotamuses, buffalo, giraffes, and even lions and porcupines. Although it is not a common event, Nile crocodiles will kill and eat humans. Nile crocodiles are strictly carnivorous, but there are unverified reports that they have been spotted eating vegetation. They certainly ingest vegetation accidentally when foraging among water plants for other prey.

Nile crocodiles have a variety of hunting techniques, ranging from simple, savage rushes to complex entrapment behaviors. For example, Nile crocodiles have been observed using their long tails to corral a small school of fish. This disorients the fish and the crocodile has an easy time catching them. They also use their powerful tails to knock larger prey into the water where the crocodile has the advantage. One of their most common hunting techniques is surprise. A crocodile waits for its prey to come down the water's edge for a drink, and then it slowly swims to the shore and lies in wait, with just its eyes above the water, a few feet from the animals head. Then it suddenly lunges out of the water and latches onto the animal's head with its powerful jaws. If it can get a firm grip with its teeth, the crocodile pulls the animal into deeper water, where it drowns its prey. Crocodiles have no way to anchor their prey once it is dead, so to get a mouthfull of meat, they bite the animal and roll over and over on their long axis until they twist off a hunk of meat. Then they bring their heads above water, flip their food into the air and grab it again, each time getting it further and further down the gullet. They usually need to rest for a few minutes before taking another bite. Sometimes, in an effort to anchor their prey, crocodiles wedge an animal between rocks or tree roots, which act to hold the prey firmly so the crocodile can tear off a chunk. This is an amazing, intelligent behavior which some say borders on a primitive form of tool use. If the skin of the prey animal is too tough for the crocodile to penetrate, it stores the dead animal in an underwater hollow until it rots enough for the crocodile to bite into it. All crocodilians have a flap of skin at the back of their throat which closes off their respiratory system when they are underwater. This allows them to open their mouths underwater without choking. They also have gizzards in which ingested stones help grind their food. Some say the stones act as a diving ballast as well.

Reproduction

Nile crocodiles mate late in the year. The male crocodile performs elaborate mating displays, much like birds do, and then approaches any receptive females. During copulation, which only lasts a minute or two, the pair usually sinks to the bottom of the lake or river. The female is usually ready to lay her eggs about two months later. At this time she comes onto land and digs a nest hole far enough away from the water to avoid any potential flooding. Then she lays a few dozen heavily calcified, chicken-sized eggs in the hole. It is said that she lays each egg on her hind foot and carefully lowers it into the hole. After laying the eggs, she covers them with organic debris and goes back to the water. During the incubation period of 2.5 to 3 months, the mother makes frequent trips to her nest, watching it carefully for the many creatures which prey on crocodile eggs. The eggs stay in the nest, with its rotting debris creating a constant temperature of over 95 degrees, until they hatch, at which time the hatchlings call for their mother. She comes and carries the young in her mouth to the water, where they follow her closely. Mother Nile crocodiles often take their young to out-of-the-way, backwater areas of their lake or river and protect them for up to two years. This is an extraordinary amount of parental care. At two years of age, the young move off to be independent, but they still must avoid the larger crocodiles, which may try to eat them. They reach sexual maturity around 8 to 12 years old.

Behaviour

The Nile crocodile lives in large communities ranging from a few dozen to a few hundred individuals, depending on their habitat. Although they live together, they engage in no group behaviors other than large feeding frenzies where all the crocodiles near a large prey animal converge on it and eat together with surprisingly little fighting. During one of these feeding frenzies, it is reported that there may be no other crocodiles within three kilometers of the event.

Crocodiles rarely venture far from the water. Only if their pool is drying up will a Nile crocodile leave in search of a new home, and when this happens the individual usually dies en route. There is a social hierarchy in the crocodile community, and the larger crocodiles are dominant. Usually male, these crocodiles drive other smaller males from potential mates and prey.

A typical Nile crocodile's day primarily consists of resting, swimming and eating. Just before dawn, they often leave the water to bask in the sun with their mouths open, so they can dissipate excess heat from the inside of their mouths in the same way a dog pants. Near midday the crocodile returns to the water, where it will feed if hungry. Crocodiles prefer to eat often, though they can go without food for many days, perhaps even a year or more. If the crocodile is not hungry, it swims the perimeter of its domain, patrolling, or rests near the shore.

The most amazing behaviors of Nile crocodiles are reproductive and feeding behaviors (see Reproduction and Food Habits).

Habitat

The Nile crocodile inhabits any wet area in tropical zones of Africa. In lakes, rivers, marshes, and ponds, the Nile crocodile is the most common and widespread crocodile.

Biomes: freshwater lake, freshwater rivers

Conservation

Status:

  • IUCN: No special status
  • CITES: Appendix I

 

Most wild populations listed by CITES on Appendix I. Ranched populations and some wild populations on CITES Appendix II.

Although not endangered and perhaps not even threatened, the Nile crocodile is very vulnerable to human intrusion. Unlike many animals, crocodiles cannot adapt to a change in habitat type. The Nile crocodile needs the water humans are polluting, the land humans are developing, and the lives poachers are taking. The Nile crocodile's currently healthy numbers could suddenly fall given too much human intrusion.

Comments

One amazing feature of crocodiles is their huge difference from other "reptiles." These distinguishing features are mostly internal. For example, they have more advanced hearts that any other reptile, controlling temperature and oxygen content in the blood stream much more efficiently. Most interesting, however, is the fact that their brains have a true cerebral cortex, allowing them to exhibit more learned, as opposed to instinctive, behaviors than most other reptiles.

Another interesting fact concerns the muscles in a crocodile's jaws. Crocodilians are capable of applying many tons of pressure with their bite, but the muscles that open the crocodile's jaws are relatively weak. Many natives of areas with crocodiles have amazed tourists by "wrestling" a live crocodile or alligator. They simply hold the crocodiles's mouth shut with their hands and the crocodile's jaw muscles aren't strong enough to open its mouth!

There are three families of Crocodylia, with 23 species total, listed below.

Family Alligatoridae

  • Genus Alligator [True Alligators]
    • A. sinensis [Chinese Alligator]
    • A. mississippiensis [American Alligator]
  • Genus Caiman [Caimans]
    • C. latirostris [Broad-snouted Caiman]
    • C. crocodilus [Common Caiman]
    • C. yacare [Caiman Yacare]
  • Genus Paleosuchus [Dwarf Caimans]
    • P. palpebrosus [Cuvier's Dwarf Caiman]
    • P. trigonatus [Schneider's Dwarf Caiman]
  • Genus Melanosuchus
    • M. niger [Black Caiman]

Family Crocodylidae

  • Genus Crocodylus
    • C. rhombifer [Cuban Crocodile]
    • C. acutus [American crocodile]
    • C. moreletii [Morelet's Crocodile]
    • C. cataphractus [African Slender-snouted Crocodile]
    • C. niloticus [Nile Crocodile]
    • C. intermedius [Orinoco Crocodile]
    • C. porosus [Indopacific Crocodile]
    • C. johnsoni [Johnston's Crocodile]
    • C. palustris[mugger or marsh crocodile]
    • C. siamensis [Siamese Crocodile]
    • C. mindorensis [Phillippine Crocodile]
    • C. novaguineae [New Guinea Crocodile]
  • Genus Osteolaemus
    • O. tetraspis [Dwarf Crocodile]

Family Gavialidae

  • Genus Gavialis
    • G. gangeticus [Gharial]
  • Genus Tomistoma
    • T. schlegelii [False Gharial]


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