Nile crocodile

Historically, the Nile crocodile was present in almost all of Africa. Nowadays, this reptile only inhabits certain regions of the African continent. Its habitat is not limited to the Nile, as it is also found in slow-moving waterways such as rivers and streams, as well as lakes, swamps, and along the coasts. Its geographical range extends from South Africa up to Egypt, passing through the Sahel belt. Thanks to its ability to swim in open sea, it colonized Madagascar, where it is still present today.

Males can weigh between 250 and 750 kg and measure 4 to 6 meters long. Some very old individuals can measure nearly 7 meters and weigh up to 1,200 kg. The smaller females weigh only between 50 and 250 kg with a size of 2 to 4 meters. The dorsal part of the body is covered with thick scales supported by bony plates serving as protective armor, the color of which ranges from black to green to brown. Those on the ventral side are white.

Its legs are short but allow it to move quickly on land, up to 17 km/h.

The front paws have 5 toes, while the hind ones have 4 webbed toes. It has a long tail flattened vertically and equipped with two rows of ridges that it uses for swimming. It is a reptile adapted to aquatic life since its eyes and nostrils are on top of its head so that they stick out of the water when it is submerged. This allows it to breathe and see its surroundings. Its eyes have a third eyelid called a nictitating membrane. This eyelid is transparent and moves horizontally, from the nasal part to the temporal part of the eye. It provides additional protection when the animal dives.

The Nile crocodile has one of the most powerful jaws in the animal kingdom. Indeed, the pressure is estimated at more than 2,000 kg/m². It has 22 conical-shaped teeth on each side of the jaw, both upper and lower. The 4th tooth is the most developed. Moreover, when a tooth breaks, it grows back automatically; this is called a polyphyodont species.

Like all reptiles, the Nile crocodile is an ectothermic animal. This means that it does not produce heat and is unable to regulate it without help from the external environment. To warm up, it exposes itself to the sun’s rays, and conversely, to avoid overheating, it immerses itself in water. This little habit allows it to maintain a body temperature between 19 and 29°C. These animals are not very active and spend more than a quarter of the day with their mouths open, warming up on the riverbanks.

If the summer conditions no longer allow temperature regulation, the Nile crocodile estivates. It digs a tunnel 3 meters long and 2 meters deep, in which it buries itself to enter a physiological state of semi-lethargy allowing for survival.

Although it usually stays underwater for only a few minutes, the Nile crocodile is an excellent freediver, able to stay underwater without breathing for up to 30 minutes. If it remains completely still, it can even stay submerged for 2 hours! This is possible thanks to the organism’s high tolerance to high concentrations of lactic acids, a chemical compound produced by the body during exertion or apnea.

They are solitary reptiles but can nevertheless coexist on the same banks. They communicate with each other using many sounds, such as bellowing, for example. There is a mutualistic relationship between the Nile crocodile and the Egyptian plover, a small bird about 20 cm long with gray feathers on its back, white on its belly, and black on its head. This means it is an interaction that is beneficial to both individuals, but not mandatory. Either one can do without this relationship. In fact, these birds peck at leftover food stuck in the crocodile’s mouth as well as leeches attached to its body. This relationship thus provides food for the bird and care for the reptile. Moreover, some Egyptian plovers are content to nest close to the crocodiles in order to benefit from their presence to scare away potential predators. These birds also serve to warn of danger, such as the approach of a human or a lion, for example.

The Nile crocodile is one of the largest and most ferocious African predators. They are super predators at the top of the hierarchy and have no predators as adults. They are opportunistic carnivores that consume a wide variety of prey. Many species are on the menu: fish, reptiles, birds, and mammals such as zebras, wildebeest, or antelopes. The young eat small prey such as amphibians and insects. The hunting technique is quite simple since they use ambush. Hidden in the water along the banks, with only the eyes and nostrils protruding, it patiently waits for a prey to come close. Then, it rushes upon it with incredible speed, grabs it firmly using its powerful jaws to drag it into the water in order to drown it. A second hunting technique consists of whipping the prey with its powerful tail to stun it. Its slow metabolism allows for long periods of fasting, which can last up to a year.

The Nile crocodile does not chew its food; it tears off large chunks of flesh violently and swallows them whole. The stomach of the Nile crocodile contains gastroliths (small swallowed stones). The current role of these gastroliths is not yet understood, and two hypotheses exist. The first suggests that these stones are swallowed to help digest food, while the second states they are used to help with diving.

The breeding season takes place during the rainy season between November and April. During this period, the males fight each other for access to the females. After that, the victorious males try to attract the females with bellowing, blowing in the water, or head movements in the water. One or two months after mating, the female lays between 25 and 85 eggs, which are buried in the soil or sand. Decomposing leaves help create the heat vital for embryo development, since a warmth of at least 28°Celsius is necessary. Additionally, the incubation temperature of each egg determines the sex of the hatchling. Indeed, a temperature between 31.7°C and 34.5°C will produce only males. In contrast, a lower or higher temperature will produce only females. The young are born after 90 days of incubation, weighing 70 grams at 30 cm long, and are generally yellow in color, although some individuals are dark green. There is parental care in Nile crocodiles because even though the female does not seem to protect the nest, the young stay with the mother for 2 years. In fact, at birth the young’s squeaks attract the mother’s attention, who then protects them from potential predators such as wading birds, pythons, hyenas, or even panthers. However, only 5% of the young will survive… Sexual maturity only occurs between 12 and 16 years of age. The lifespan ranges between 70 and 100 years.

The Nile crocodile is unfortunately among the endangered species. That’s why many clutches are collected and incubated in a lab, safe from predators. The main threat they face is poaching for their skin, which is used in luxury leather goods…

Discover other species from the African continent: rhinoceros