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|CROCODYLUS NILOTICUS (The Nile Crocodile)|
Considerable variation exists throughout the range of the Nile crocodile. Generally, it is a large crocodilian, averaging 5 m in length but reportedly reaching 6 m in rare instances. There are dubious reports of 7 m animals having existed, but these are hard to verify. There is some evidence that Nile crocodiles in cooler countries (eg. South Africa) reach slightly smaller adult sizes (4 m). There are two known population of dwarf Nile crocodiles living on the extreme limits of the species' range, in Mali and even the Sahara Desert! Due to suboptimal conditions, adults average between 2 and 3 metres. Juveniles are dark olive brown with black cross-banding on the tail and body. This banding becomes fainter in adults.
This species digs hole nests up to 50cm deep in sandy banks, several metres from the water. These may be in close proximity to other nests. Timing of nesting behaviour varies with geographic location - it takes place during the dry season in the north, but at the start of the rainy season further south, usually from November through to the end of December. Females reach sexual maturity around 2.6 m, males at around 3.1 m. Females lay around 40 to 60 eggs in the nest, although this number is quite variable between different populations. Females remain near the nest at all times. Incubation time averages 80 to 90 days (ranges from 70 to 100 days), after which females open the nest and carry the juveniles to the water. Both males and females have been reported to assist hatching by gently cracking open eggs between their tongue and upper palate. Hatchlings remain close to the juveniles for up to two years after hatching, often forming a creche with other females. As with many crocodilians, older juveniles tend to stay away from older, more territorial animals.
Despite the vigilance of the female during the incubation period, a high percentage of nests are raided by a variety of animals, from hyaenas and monitor lizards to humans. This predation usually occurs when the female is forced to leave the nest temporarily in order to thermoregulate by cooling off in the water.
Diet and eating behavior
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 (yards) 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 pieces of meat from between the crocodile's teeth. This has proven hard to verify, and may not be a true symbiotic relationship.
Differentiating between Crocodiles and Alligators
Shape of the Jaw
The easiest way of telling apart crocodiles from alligators, is to look at their noses. Alligators (and caimans) have a wide "U"-shaped, rounded snout (like a shovel), whereas crocodiles tend to have longer and more pointed "V"-shaped noses. The broad snout of alligators is designed for strength, capable of withstanding the stress caused to bone when massive force is applied to crack open turtles and hard-shelled invertebrates which form part of their diet. Conversely, the pointed snout of a crocodile isn't quite as strong as the alligatorine shape, but the crocodile is still capable of exerting massive biting power. Crocodile jaws can be thought of as being more generalised - ideal for a wide variety of prey. The full extent of the way jaw shape influences diet isn't particularly well studied in crocodilians, but it's obvious that a very thin nose like a gharial's is much better at dealing with a fish than a turtle! There are 23 species of crocodilians though, and this simple broad vs. narrow rule doesn't always work.
Placement of Teeth
In alligators, the upper jaw is wider than the lower jaw and completely overlaps it. Therefore, the teeth in the lower jaw are almost completely hidden when the mouth closes, fitting neatly into small depressions or sockets in the upper jaw. This is particularly apparent with the large fourth tooth in the lower jaw. In crocodiles, the upper jaw and lower jaw are approximately the same width, and so teeth in the lower jaw fit along the margin of the upper jaw when the mouth is closed. Therefore, the upper teeth interlock (and "interdigitate") with the lower teeth when the mouth shuts. As the large fourth tooth in the lower jaw also fits outside the upper jaw, there is a well-defined constriction in the upper jaw behind the nostrils to accommodate it when the mouth is closed.
There are other another few methods that may enable you to do a correct identification however those require considerable proximity to the reptile :)
This shot of a juvenile Nile Crocodile was taken in the Wroclaw Zoo, Poland. There is some glare of lighting on the croc's shiny nasal bridge and the snout is not completely in focus. The reason I posted this picture is because of the interesting POV.
Thanks for Looking!!
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