The Nile Crocodile is a large crocodilian native to freshwater habitats in Africa, where it is present in 26 countries.
The Binomial name Crocodylus niloticus is derived from the Greek, kroke ('pebble'), drilos ('worm'), referring to its rough skin; and niloticus, meaning 'from the Nile River'. It is also sometimes referred to as the African crocodile, Ethiopian crocodile, common crocodile, or the Black crocodile.
The Nile Crocodile is amongst Africa's most feared predators, and rightly so. It has one of the strongest bites in the animal kingdom and can take down a grown human being easily. According to experts, a Nile Crocodile's bite exerts a force that is 8 times more powerful than that of the fearsome Great White shark and 15 times greater than that of a Rottweiler.
The Nile Crocodile is the largest and most aggressive crocodilian in Africa, and is generally considered the second-largest crocodilian, after the saltwater crocodile.
Features and Characteristics
The Nile Crocodile is a quadruped with four short, splayed legs, a long, powerful tail, a scaly hide with rows of ossified scutes running down its back and tail, and powerful, elongated jaws.
Adult Nile Crocodiles have a dark bronze colouration above, with faded blackish spots and stripes appearing down the back and a dingy off-yellow on the belly, although mud can often obscure the crocodile's actual colour. The flanks, which are yellowish-green in colour, have dark patches arranged in oblique stripes in highly variable patterns.
Some variations occur relative to environment; crocodiles 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. Nile Crocodiles possess green eyes. The colouration also helps to camouflage it; juveniles are grey, multicolored or brown, with dark cross-bands on the tail and body. As it matures Nile Crocodiles become darker and the cross-bands fade especially those on the upper body.
The mouth of a Nile Crocodile is filled with 64 to 68 sharply pointed, cone-shaped teeth (about a dozen less than alligators have). For most of a crocodile's life, broken teeth can be replaced. Crocodile teeth are not used for tearing up flesh, but to sink deep into it and grasp on the prey item.
Like all crocodiles, sexual dimorphism is prevalent, 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 50cm longer on average at sexual maturity and grow more so than females after becoming sexually mature. Adult male Nile Crocodiles usually range in length from 3.3 to 5.0m long; weighing 150 to 700kg. Mature female Nile Crocodiles typically measure 2.2 to 3.8m in lengths and the average female weighs 40 to 250kg.
Hunting and Diet
Their reputation as vicious man-eaters is only certainly deserved. Due to its habitat on the banks of rivers, Nile Crocodiles have frequent encounters with humans, and they are not fussy about which meat they eat. Fish are the mainstay of these carnivores but will also kill and eat small hippos, porcupines, buffalos, zebras, other crocodiles and any other animal they can lock their jaws on (basically anything that moves), including the carcasses of already dead animals. A local washing his clothes in a river may look just as tasty as a herd of migrating wildebeest. Estimation has it that this species of crocodile is solely responsible for up to 200 human deaths a year.
Nile Crocodiles are opportunistic apex predators, a very aggressive species of crocodile, that are capable of taking almost any animal within their range. In the water, this animal 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 prey.
These predators can wait hours, days, and even weeks for the suitable moment to attack. They wait for the opportunity for a prey item to come well within attack range. Even swift prey are not immune to attack.
No matter where they attack prey, Nile Crocodile and other crocodilians take practically all of their food by ambush, needing to grab their prey in a matter of seconds to succeed.
They have an exothermic metabolism, so can survive for long periods between meals though when they do eat, they can eat up to half the weight of their body at a time. However, for such large animals, their stomachs are relatively small, not much larger than a basketball in an average-sized adult, so, we put it that, they are anything but voracious eaters. They can survive several months without food.
The Nile Crocodile mostly hunts within the confines of waterways, attacking aquatic prey or terrestrial animals when they came to the water to drink or to cross. They drag the prey into the water and drown them. Occasionally, a Nile Crocodile quietly surfaces so that only its eyes (to check positioning) and nostrils are visible, and swims quietly and stealthily towards its mark. The attack is unpredictable and sudden. The crocodile lunges its body out of water in practically the blink of an eye and grasps its prey. On some other occasions, more of its head and upper body is visible, especially when the terrestrial prey animal is on higher ground, to get a sense of the direction of the prey item.
These crocodiles eat rocks/stones, which may account for 1% of total body weight. Although, this is most common amongst adult Nile Crocodiles, so as to help maintain buoyancy in the water. Ingesting these stones is also useful when laying on the river bottom and also useful to lower the center of gravity and gain stability in the water. Added weight also helps to subdue struggling prey.
The youngest juveniles are insectivorous, they consume water-bugs, dragonfly nymphs, beetles, spiders, mole crickets, frogs, snails. Older juveniles take more small vertebrates and invertebrates; they eat freshwater crabs, snails, toads, frogs, turtles, small birds and rodents.
The Nile Crocodile are gregarious animals, they tolerate the nearness of other Nile Crocodiles. They are relatively social crocodiles. They share basking spots and large food sources, such as schools of fish and big carcasses.
Generally, Nile Crocodiles are relatively inert creatures, as are most crocodilians and other large, cold-blooded creatures. They spend their time continuously basking with their jaws open, if it were a sunny day. If their jaws are bound together in the extreme midday heat, Nile Crocodiles may easily die from overheating. Although, they can remain motionless for hours on end, Nile Crocodiles are said to be constantly aware of their immediate surrounding and aware of the presence of other animals.
They are known to usually dive for only a few minutes at a time, but can swim under water for up to 30 minutes if threatened; and if they remain fully inactive, they can hold their breath for up to 2 hours (which is due to the high levels of lactic acid in their blood).
These reptiles are mainly nocturnal. Male Nile Crocodiles are highly territorial, they patrol and defend their territories, which often include parts of the shoreline, extending about 50 meters into the water. Their strict hierarchy is determined by size.
They are exceptionally fast runners, and in general, these crocodiles have very quick reflexes, but unfortunately, tire quickly.
What is fascinating about these cold-blooded predators is that they possess extraordinary parental instincts. Most other crocodiles will simply lay their eggs and move on, but the female and male Nile Crocodiles assist their hatchlings by gently cracking the eggs in their mouths. The females also use their enormous jaws to transport their hatchlings safely to 'nursery pools', where they fiercely guard them against other predators.
Nile Crocodiles exhibit polygynous mating habits, where one male mates with a number of females. Male Nile Crocodiles usually attract receptive females, making a wide variety of noises through bellowing, slapping their snouts in the water or blowing water out of their noses. Meanwhile, larger males are usually more successful in finding mates.
The nesting season in this species is between November to December. During this period, a female Nile Crocodile digs a nest, which is a hole in a riverbank or sandy river bed. Then, 25-80 eggs are laid and incubated for 80-90 days. When the hatching time approaches, the female opens the nest, carrying her offspring to the water. After a while, the young join a creche of juveniles, which is catered after by females. The hatchlings can remain in this creche for the first 2 years of their lives. Nile Crocodiles are sexually mature at 12-16 years old.
Distribution and Habitat
The Nile Crocodile is widely distributed throughout Sub-Saharan Africa, occuring mostly in the central, eastern and southern regions of the continent, and lives in different types of aquatic habitats such as lakes, swamps, rivers, and marshlands. Although capable of living in saline environments, this species is rarely found in saltwater, but occasionally inhabits deltas and brackish lakes.
They are presently the most common crocodilian in Africa, and is distributed throughout much of the continent. This specie's historic range was however even wider. They were found as far north as the Mediterranean coast in the Nile Delta and across the Red Sea in Palestine and Syria. The Nile Crocodile has historically been recorded in areas where they are now regionally extinct.
Today, they are widely found in Somalia, Ethiopia, the Democratic Republic of Congo, the Central African Republic, Equatorial Guinea, Tanzania, Rwanda, Burundi, Zambia, Gabon, Zimbabwe, Angola, South Africa, Malawi, Mozambique, Namibia, Sudan, South Sudan, Botswana, and Cameroon. Nile Crocodiles are absent from most of West and Central Africa.
Threats to Survival
The primary threats to this species have to do with humans, as expected. Thus, the reptile attracts hunters for its skin, which is used in the production of high quality leather.
On the other hand, being large and dangerous predators, the Nile Crocodiles face aggression from humans, who destroy their nests and frequently kill the crocodiles. Attempting to remove caught fish from fishing nets, these animals occasionally damage the nets, causing conflict between the crocodiles and fishermen.
In some parts of Africa, the animals are threatened by invasion of exotic plants that shade and supplant their nesting sites, cooling their eggs, which can potentially bring to an all-female population (the sex of the crocodiles is largely determined by the temperature).
These creatures were nearly hunted to extinction in the 1940s to 1960s but have since seen a healthy rise in their population. Classified as Least Concern (LC) on the IUCN Red List, this reptile is currently not endangered. By estimation, the population of the Nile Crocodile varies from 250,000 to 500,000 individuals.
Average lifespan of the Nile Crocodile is approximately 45 years in the wild, may live up to 80 years in captivity.
Ecology and Preservation
Nile Crocodiles are ecologically important as predators. They help the environment by keeping barbel catfish, which are predators themselves, in check. Barbels eat other fishes which are the diet of more than 40 species of birds. If birds leave an area because there are no edible fish, the amount of bird droppings, which provides nutrients for the fish, declines and the food chain is disrupted.
Unfortunately, the Nile Crocodile population suffers from pollution, hunting, and entanglement in gill nets.
Nile Crocodile Fun Facts
- Crocodiles have the strongest bite in the animal kingdom. And the Nile Crocodile is no different, with a powerful bite force as high as 5,000 lbf (22,000 N).
- The sex of Nile Crocodile hatchlings is determined by the temperature at which the eggs incubate. At 30°C or less, they will be mostly female; at 31°C they will be mixed; at 32°C and more, they will be mostly male.
- They are the most vocal of reptiles. Among more than five different calls are the deep, vibrating bellow of courting males and the 'peeping' of babies inside the egg, encouraging the female to excavate the nest.
- Large Nile Crocodiles swallow stones, known as gasthroliths. These act as ballast, helping them to balance their body underwater.