1 – WildlifeCampus Snakes and Reptiles of the Lowveld Course Module # 3 - Component # 1 Crocodiles, Monitor Lizards & Chameleons Introduction to Crocodiles One of the simplest creatures to identify, regardless of its size. Throughout Africa, there are no alligators, only Caiman and Crocodiles and within South Africa, there are only Crocodiles. The main difference between crocodiles in the wild is size, ranging from 1.2 m to 6.5 - 7 m. There is debate over what the largest species of crocodile is in the world. The largest crocodile species on average is the Saltwater Crocodile. All crocodile species are carnivorous as adults, but as hatchlings/juveniles, they will eat nearly everything they can swallow, from fish to frogs and insects. The main diet of smaller crocodile species or sub-adult Nile Crocodile is fish, terrapins, frogs and other aquatic species. Large species of crocodile feed mainly on game. Occasionally, humans have been known to be taken. The key difference between crocodiles and alligators is the fourth mandibular tooth. This tooth is only visible in crocodile species. There is only one species in the course region, that being the Nile Crocodile (Crocodylus niloticus). Crocodiles, Monitor Lizards & Chameleons © Copyright This course material is the copyrighted intellectual property of WildlifeCampus. It may not be copied, distributed or reproduced in any format whatsoever without the express written permission of WildlifeCampus 2 – WildlifeCampus Snakes and Reptiles of the Lowveld Course Nile Crocodile Classification Kingdom Animalia Phylum Chordata Class: Reptilia (Reptiles) Order: Crocodylia (Crocodylians) Family: Crocodylidae (Crocodiles) Genus: Crocodylus (Crocodile) Species: niloticus (Nile crocodile) Description: As this is the only species that occurs in this range, there is no chance for error. They are identifiable as crocodiles because of the exposed fourth mandibular tooth when the jaw is closed. The nostrils are situated on top of the jaw as well as the eyes. Crocodile size Crocodiles, Monitor Lizards & Chameleons © Copyright This course material is the copyrighted intellectual property of WildlifeCampus. It may not be copied, distributed or reproduced in any format whatsoever without the express written permission of WildlifeCampus 3 – WildlifeCampus Snakes and Reptiles of the Lowveld Course The body is covered in bony plates or scales, many of which are keeled. This allows them to move through water creating little waves as the next scale breaks up the wave created by the former scale. By having this they can ambush prey highly successfully. As hatchlings, they are green with some black blotches and a yellow to cream belly. As they mature into adults, they become darker and will eventually be a plain olive- brown to grey. The belly retains the yellow to cream colouration. The tail cannot be shed or regenerated and has two rows of dorsal scales to the end of the tail. The body is longer than the tail by around 10% of the overall body length. Crocodiles are measured from the tip of the nose to the end of the tail. Habitat: Crocodiles are present in permanent water bodies and will even be within mangrove swamps or river mouths. Despite this, they prefer to be in freshwater. Crocodiles, Monitor Lizards & Chameleons © Copyright This course material is the copyrighted intellectual property of WildlifeCampus. It may not be copied, distributed or reproduced in any format whatsoever without the express written permission of WildlifeCampus 4 – WildlifeCampus Snakes and Reptiles of the Lowveld Course Gender: As is the case in most “lizard” looking species, determining the sex is difficult. There is no real difference visually between the sexes at any age, and the only reliable method of sexing is via probing. If observing crocodiles, one could determine the sex based on behaviour. During the breeding season, the male will ‘vibrate’ his body, causing the water to “jump” around him. If a crocodile is protecting a nest, it is a female. Sexual maturity is only reached at around 12-15 years of age. Diet: Crocodiles are carnivorous. As hatchlings though, they may eat various insects such as locusts, but they prefer fish and frogs. As they mature, they will eat terrapins and eventually large game and man. Carrion is also eaten. Crocodiles, Monitor Lizards & Chameleons © Copyright This course material is the copyrighted intellectual property of WildlifeCampus. It may not be copied, distributed or reproduced in any format whatsoever without the express written permission of WildlifeCampus 5 – WildlifeCampus Snakes and Reptiles of the Lowveld Course Habits: On hot days, crocodiles will lie on the riverbanks to bask. If they get too hot, they will leave their mouths open to cool via evaporation. They do spend large amounts of time in the water. As juveniles, they will remain in the protection of the reeds and other vegetation, for fear of being eaten by larger crocodiles. Hatchlings and specimens up to 4 or 5 years of age spend more time out of the water, for the same reason. It has been recorded that crocodiles will communally hunt for fish, forcing them to shallower waters. If large game is captured, they pull the food into the water to drown. Crocodiles are unable to chew the food, so they must tear off pieces that they can easily swallow. At times, they may bite over the animal to soften or tenderize it. It has also been recorded where one crocodile will hold the prey firm, whilst others bite a chunk and then spin to tear it off. Most commonly caught wild game are antelopes, but some buffalo and zebras have not escaped and been eaten. They have a gular flap and valved nostrils that close off while feeding underwater to ensure they do not drown or take any water into the lungs. While swimming, the tail provides the propulsion and the rear webbed feet are like rudders. They swim effortlessly and almost undetected. In wait of prey, they will just keep the nostrils and eyes above water and remain motionless waiting for herds to come and drink. Only the dominant male will mate with the females in his territory. Mating occurs in July and August and is always done in water. In around November, she will lay the eggs in a nest she dugout. They will usually keep re-using the same nest year after year. The nest is situated above the floodwaters and in well-drained soil. It will be relatively close to the water’s edge, as the entire time she will guard the eggs. Sometimes Nile Monitors will attempt to raid the nest, but it is a very risky affair. After about three months, in which the females have not eaten and only gone to the river to drink, the hatchlings emerge. They make a squeaking noise to call the female to the nest. She will slowly excavate the nest and remove the babies. She takes them down to the water into a restricted area. They will remain in this area for up to 2 months under the guard of the female. After this the hatchlings are to fend for themselves and the protection is radically reduced. The incubation temperature, like tortoises, determines the sex of hatchlings. However, crocodiles are the reverse. The hotter the temperature the more males will hatch. Males are produced at incubation temperatures between 31 oC - 34 oC, females are between 26 oC - 30oC. Crocodiles, Monitor Lizards & Chameleons © Copyright This course material is the copyrighted intellectual property of WildlifeCampus. It may not be copied, distributed or reproduced in any format whatsoever without the express written permission of WildlifeCampus 6 – WildlifeCampus Snakes and Reptiles of the Lowveld Course Distribution: Distribution of the Nile Crocodile in this region Crocodiles, Monitor Lizards & Chameleons © Copyright This course material is the copyrighted intellectual property of WildlifeCampus. It may not be copied, distributed or reproduced in any format whatsoever without the express written permission of WildlifeCampus 7 – WildlifeCampus Snakes and Reptiles of the Lowveld Course Monitor Lizards Family Varanidae: Monitor Lizards are of the Order Squamata and the Sub-Order Sauria and fall under the family Varanidae. We have 2 species of Varanid in South Africa and both occur in all the regions covered. It is a relatively small family having only 46 Species. Some of the largest and more famous lizards such as the Komodo Dragon (Varanus komodoensis) are included in this family. The Komodo dragon, from Java, reaches a length of approximately 3 m and preys on animals such as deer. Moving back to Africa, 5 species occur on the continent and only 2 reach the sub- continent. Most of the species are semi-aquatic, and most are predators. The size range of this family is from 200mm to 3m+. The smaller monitors are mainly insectivorous, while the rest are carnivorous. Crocodiles, Monitor Lizards & Chameleons © Copyright This course material is the copyrighted intellectual property of WildlifeCampus. It may not be copied, distributed or reproduced in any format whatsoever without the express written permission of WildlifeCampus 8 – WildlifeCampus Snakes and Reptiles of the Lowveld Course Description: In appearance, the monitors are prehistoric looking. They have powerful limbs and incredibly strong, sharp claws. The tails are similar to chameleons in that the tail cannot be shed or regenerated. They are usually laterally compressed, similar to the Nile Crocodile. The scales are bead-like and do not overlap one another. Shedding is done in bits, unlike snakes. Prey items are normally swallowed whole and headfirst as in the case of snakes. If eggs are eaten, they will normally crack them in their mouths, swallowing the lower half of the shell and discarding the upper half held by extremely powerful jaws. Reproduction: Copulation and egg-laying are seldom observed in this family as they are extremely secretive.