Lords of the Waterways: Studying Nile Crocodiles

Very few visual examples of a time when giant reptiles walked the earth can be seen today apart from fossils. However, there do exist animals that reflect the power and majesty of those ancient creatures. The order Crocodilia makes up a good portion of these prehistorically detailed animals. They are successful animals, with a population present in every continent except for Antarctica (a land much too cold for any reptile). They are superb predators, designed to ambush and overpower their prey. They have few enemies, and most of the species reside at the top of the food chain. However, like many other apex predators, they have come into negative contact with humans. Some large species have gained a notorious reputation for being man-eaters, and humans themselves have become a major enemy to crocodiles as they hunt the species down for their skin and sometimes also for food. There consist 3 families within the order; Crocodylidae, Alligatoridae, and Gavialidae. The crocodiles, Crocodylidae, are the most aggressive as well as generally the largest. In Africa, one such species has gained fame for its aggressive behavior; the species which will be studied in this article, the Nile crocodile.

The Nile crocodile (Crocodylus niloticus) is found throughout Africa, from the Nile river delta, the Mediterranean coast, Tunisia and Syria, to isolated populations found in the interior of Mauritania, Southeastern Algeria, and Northeastern Chad.[1] They are also found in West Madagascar. Lakes, marshes, rivers, lagoons, and estuaries are all common homes for the species, although the population in Madagascar is known for living in caves. The species is not known to adopt a marine lifestyle, though there have been reports of the Nile species swimming rather far away from land in coastal areas.

They are among the largest of all modern crocodiles, attaining an average length of 16 ft and weight of around 500 pounds. However, older males can reach extremes of 20 ft in length and nearly a ton in weight.[2]Males are larger than females, as seen in all other crocodilians. One individual shot in Mwanza, Tanzania, was 21.3 feet long and weighed 2,400 pounds.[3]Similarly large individuals are reported but few as large as the record holder are observed.

Although agile and deadly in water, crocodiles tend to be slow on land. They can reach fast speeds for very short distances but quickly run out of energy as their small legs cannot support their great weight for long. These bursts of speed can still be effective, though, as crocodiles can catch nearby prey off guard in this way. However, this is a tactic that would prove more useful for younger individuals. Crocodiles possess by far the strongest jaws in the animal kingdom. Nile crocodiles can bite down with a pressure of 3000 pounds per square inch (and sometimes more). Like other crocodilians, however, the muscles they use to open their mouths are very weak. The crocodile heart has three chambers, including a relatively elongated cardiac septum. There are valves made of connective tissue within the heart which control the blood flow. They are controlled by the amount of adrenaline in the bloodstream so that when the animal is relaxed, the valves close. This results in more blood flow to the lungs, allowing the animal to hold its breath for up to 2 hours when underwater.[4]

Nile crocodiles are apex predators. They have few enemies and prey on a great variety of animals. Nearly any animal which comes to drink at the water’s edge is a potential prey item for an adult crocodile, except for very large animals like elephants or rhinoceros, although there was a case where a pack of Nile crocodiles hunted and killed an adult female black rhinoceros.[5] This same pack behavior (a trait few crocodilians possess) allows for the hunting of similarly large animals like the hippopotamus. More common prey would include antelope, gazelles, waterbuck, zebra, wildebeest, Cape buffalo, and other mammals. In times of prey shortage, crocodiles are known to attack and kill other predators such as cheetahs, leopards, and even lions (lions are also known to prey on crocodiles during these shortages of food).[6]Crocodiles usually hunt land animals by waiting for prey to come to the water’s edge for a drink. They then approach their selected prey underwater and strike from as close as possible, clamping their powerful jaws onto the prey item and dragging it underwater to be drowned.

Crocodiles have few natural competitors due to their large size, bite strength, and scaly armor. However, their enemies tend to be just as dangerous as they are. The hippopotamus is a threat due to its large size and dangerous bite; a hippo’s sharp teeth can easily slice up most animals daring enough to attack one. However, aggression between the two species is not very common, as the two tend to live in their own areas of a lake or river. On occasions, the two populations may be forced to live together due to prolonged heat drying up their water and not show much aggression to each other. Still, there are cases of hippos killing crocodiles and crocodiles preying on younger hippos. As stated before, crocodiles hunting in packs can attack and kill hippos, though this is exceedingly rare. Another species crocodiles compete with is the lion. Unlike the relationship mugger crocodiles and Bengal tigers have in India (where the tiger tends to be the more dominant predator), the Nile’s larger and more aggressive species does not seem to show much fear for the native big cat. Given the opportunity, Nile crocodiles will attempt to steal kills from lions which make the mistake of keeping their kill too close to bodies of water. The usual result is a nonviolent confrontation, with the larger and/or healthier animal winning the meal. However, the two species can certainly take the confrontation to a more aggressive level. Much like before, the winner is usually determined by which individual is healthier or larger, although the number of crocodiles and lions present at the site can also be a determining factor. As stated previously, lions and crocodiles prey on each other when they face food shortages with more common prey. Nile crocodiles may also find threats within their own species, as crocodiles are known to be cannibalistic. Also, although Nile crocodiles are fairly social compared to other crocodilians, they may also face competition from larger individuals who do not feel the need to share their food. Generally, however, adult Nile crocodiles have no common threats. Anything which nears or enters their waters puts itself in great risk.

The social life of Nile crocodiles is a little more complex than that of other species. As a result of their pack behavior when hunting, they also tend to share their meals. The larger, more powerful crocodiles tend to eat first, though at times it may seem that several differently-sized individuals will eat together without any problems. Mating season takes place in the months of June and July.[7]The males slap their snouts on the water and make a variety of sounds to attract females. Females tend to go for the bigger, stronger males. After pairing up, they rub their jaws together (possibly as a form of expression). About two months later, the female lays eggs and the parents protect the eggs until the end of the incubation period. The eggs are kept in sand to incubate them.The determiner of the sex of the offspring is temperature, with temperatures of 31-33 degrees Celsius or so producing males and anything below or above that range producing females.[8]When the offspring are close to hatching, they make sounds which alert the mother. She then digs open the nest and carries the babies into the water. She may occasionally have to break open the shells for the babies by rolling the egg around in her mouth. Mothers will protect the young for up to 2 years or so. If other females made their nests nearby, the mothers may protect each other’s offspring, forming a protective colony for the young.

Like many other crocodilians, Nile crocodiles have suffered as a result of the excessive hunting humans carried out. They came close to extinction from the 1940’s through the 1960’s. Thankfully, local and international protections helped the species make a comeback and the populations are well-established once more (though not to the same extent as they originally were). Pollution, habitat loss, and continuous hunting are still problems for the species in some areas, though.

Crocodiles are superb survivors. They lived through the past events which wiped out many animal species and continue to be successful today. Their power and aggression sometimes get them into trouble with humans, but their ancient details and survival tactics also make them very interesting to us. They are strong, and tend to dominate in regions where they live. With our continued protection, these survivors will live on for many more years to come, continuing the legacy they began long ago.

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[1] “The Nile Crocodile.” Reptiles.net. N.p., 01/25/2007. Web. 21 Nov 2010.

 

[2] “Nile Crocodile.” National Geographic.com. National Geographic Society, 2010. Web. 21 Nov 2010.

[3] Wood, The Guinness Book of Animal Facts and Feats. Sterling Pub Co Inc (1983)

[4] Thomas, Abbie. “Secret of the Crocodile Heart.” abc.net.au. N.p., 2010. Web. 22 Nov 2010.

[5] Guggisberg, C.A.W. (1972). Crocodiles: Their Natural History, Folklore, and Conservation. p. 195.

[6] “The Lion.” DesertUSA.com. N.p., 2010. Web. 21 Nov 2010.

[7] Sharp, Mary. “Life Cycle of a Nile Crocodile.” eHow.com. N.p., 24/05/2010. Web. 22 Nov 2010.

[8] Coupe, Sheena. Encyclopedia of Reptiles and Amphibians. San Diego, CA: Academic Press, 1998.