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Nile Crocodile


Image (c) Adam Britton, crocodilian.com

Africa's largest crocodile


Order: Crocodylia

Family: Crocodylidae

Subfamily: Crocodylinae

Genus & Species: Crocodylus niloticus

APPEARANCE

The Nile crocodile is the largest of the four crocodile species found in Africa. They have a maximum length of 20 ft 5 in (6.2 m) from the head to the tip of the tail. They usually weigh 500 lbs (225 kg) but will reach weights of up to 1650 lbs (730 kg). The Nile crocodile is the best known of all of the crocodile species. It is feared as a great man-killer, and its large, stocky body doesn't help its reputation. The snout is long and broad and ends in nostrils which can close underwater. The eyes have a third eyelid which protect them while underwater. The eyes, ears, and nostrils are found on the same plane on the top of the head, allowing the crocodile to be completely submerged underwater while still being able to see, smell, and hear. The teeth are long and conical. The teeth on the top jaw are in line with the bottom jaw, a feature which distinguishes all crocodiles from alligators. The fourth lower tooth is larger than the others and can be seen when the mouth is closed. Nile crocodiles have 66 teeth.

The Nile crocodile has short, squat legs which end in sharp claws. The tail is very long. Old crocodiles are a dark uniform green in colour, with darker crossbands on the tail. The skin is rough, scaly, and waterproof. It prevents dehydration and loss of body salt. The back and tail are covered in rows of knobs. The skin is classic: it has no osteoderms (bony plates) under the skin. For this reason the skin is highly valued. Nile crocodiles have a four-chambered heart like a bird, but they are still cold-blooded and rely on the sun for heat. They have a special throat pouch which allows them to eat underwater. They have great vision; the pupils are vertical slits which widen at night. The Nile crocodile has an average life span of 45 years in the wild, 80 in captivity.

HABITAT

The Nile crocodile is found throughout most of Africa, from Egypt to South Africa. As its name suggests, it is present in the Nile River. It is absent from the Sahara Desert and in 1900 was exterminated from Seychelles. It is even found in Madagascar. Nile crocodiles can be found in rivers, lakes, waterholes, mangrove swamps, estuaries, and freshwater marshes. They are mostly aquatic, but travel easily on land. During the wet season they travel long distances on land, returning when the floodwaters subside. During the day they can be found basking along riverbanks with their mouths open. While they bask, Egyptian plovers enter their mouths and clean their teeth. They are social animals, and will work together to dig tunnels and cool down.

FOOD

Nile crocodiles have voracious appetites. They feed on animals which come to the water to drink. These include zebras, hippos, wildebeest, porcupines, pangolins, and birds. They feed mainly on fish, including the barbel catfish. They will also eat other crocodiles and carrion. They sometimes team up to hunt. When an animal comes to the riverbank, the Nil crocodile attacks, seizing the animal and dragging it underwater until it drowns. It cannot chew, so the prey is stuck underneath a log to rot. Nile crocodiles eat the entire animal, including bones, antlers, etc. Pebbles are sometimes swallowed to aide in digestion. They have been known to attack man. They have a slow metabolism.

ENEMIES

Few animals are willing to prey on the Nile crocodile except for other Nile crocodiles and humans. They have been overhunted by humans for their skin, which is good for tanning, and their meat. Habitat destruction also dwindles their numbers. The young are preyed upon by Nile monitor lizards, marabou storks, herons, ibises, turtles, and catfish. Nile crocodiles are not endangered.

BREEDING

Males become sexually mature at 10 ft (3 m 10 years of age) and females at 6.5 ft (2 m 10 years of age). The breeding season is July, where they mate in shallow water. The female lays 30-80 eggs in a nest of rotting vegetation near the water's edge. The eggs hatch after an incubation of 2-3 months. If the nest was below 85 F during this period, then all the hatchlings are female. Above 95 F male. Between 85 F and 95 F both male and female. When it is time to hatch, either parent helps to open the eggs by cracking them in its mouth. They are then carried to the water. They remain in the water for several weeks. Hatchlings are 12 in (30 cm) long and are dark olive green with darker crossbandings on the body and tail.

RELATIVES

There are 23 species of crocodilians found worldwide. There are at least seven proposed subspecies: C. n. africanus, C. n. chamses, C. n. corviei, C. n. madagascariensis, C. n. niloticus, C. n. pauciscutatus, and C. n. suchus.

RESOURCES CITED

1. "Nile Crocodile" Animal Fact File, USA, IM Pub
2. "Nile Crocodile" Animal Card, 1975, Italy
3. "Crocodile" Funk & Wagnall's Wildlife Encyclopedia, vol 5, pg 553, 1974, NY
4. "Alligator" Funk & Wagnall's Wildlife Encyclopedia, vol 1, pg 29, 1974, NY
5. www.seaworld.org/animal_bytes/crocfc.html
6. www.seaworld.org/animal_bytes/crocodileab.html
7. bvsd.k12.co.us/schools/BHS/science/zoo/areas/reptilia/Nile_crocodile.html
8. www.phillyzoo.org/pz0178.htm
9. www.libra-mmsystemh.demon.nl/Html/pg_nile_croc_att.htm
10. www.flmnh.ufl.edu/natsci/herpetology/brittoncrocs/csp_cnil.htm

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