Crocodiles, Lizards & Chameleons

Transcription

1 Advanced Snakes & Reptiles 1 Module # 3 Component # 1 Crocodiles, Monitor Lizards & Chameleons Introduction to Crocodiles One of the simplest creatures to identify regardless of it's size. Throughout Africa there are no alligators, only Caimen & Crocodiles and within South Africa there are only Crocodiles. The main difference between crocodiles in the wild is size, ranging from 1.2m to 6.5 to 7m. There is a lot of debate as to what the largest species of crocodile is in the world. The largest crocodile species on average is the Salt Water Crocodile. All crocodile species are carnivorous as adults, but as hatchlings / juveniles they will eat nearly everything they can swallow, from fish to frogs to insects. The main diet of smaller crocodile species or sub-adult Nile Crocodiles is fish, terrapins, frogs and other aquatic species. Large species of crocodile feed mainly on game and 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)

2 Advanced Snakes & Reptiles 2 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 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.

3 Advanced Snakes & Reptiles 3 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 fresh water. 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 years of age. Diet: Crocodiles are carnivorous. As hatchlings though, they may eat various insects such as locusts, but they prefer fish & frogs. As they mature they will eat terrapins and eventually large game and man. Carrion is also eaten. Habits: On hot days the crocodiles will lie on the banks basking. 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 have to tear off pieces that they can easily swallow. At times they may bite over the animal to soften or tenderise 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 under water 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.

4 Advanced Snakes & Reptiles 4 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 dug out. 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, similar to tortoises, determines the sex of hatchlings. However, crocodiles are the reverse. The hotter the temperature the more males will hatch. Male are produced at incubation temperatures between 31 o C - 34 o C, females are between 26 o C - 30 o C. Distribution: Distribution of the Nile Crocodile in this region

5 Advanced Snakes & Reptiles 5 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 3m and preys on animals such as deer. Moving back to Africa there are 5 species that 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. Description: In appearance the monitors are prehistoric. They have powerful limbs and incredibly strong sharp claws. The tails are similar to chameleons in that the tail cannot be shed or regenerated and are usually laterally compressed, similar to the Nile Crocodile. The scales are bead like and do not overlap one another and shedding is done in bits, unlike snakes. Prey items are normally swallowed whole and head first 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 & egg laying is seldom observed in this family as they are extremely secretive. Even captive raised specimens of Rock Monitor were still shy and often stopped when they noticed they were being watched during copulation. Male combat is known within the family, but it is more of a wrestling match, seldom if ever, inflicting severe damage to each other. Both species of varanid in South Africa are protected and permits are required to be kept in captivity. There are 2 species that occur in the region:- 1. Nile Monitor - Varanus niloticus 2. Rock Monitor - Varanus albigularis albigularis

6 Advanced Snakes & Reptiles 6 Nile Monitor Varanus niloticus Other Names: Water monitor, Water Likkewaan, Water Leguaan or Leguaan. Description: This is the larger of the two indigenous species of varanid that are extremely powerful and normally more aggressive than the Rock Monitor. They have extremely strong legs and claws that are often used in defence, but aid in climbing and digging up nesting sites of other reptiles. They are not averse to trying to steal a few crocodile eggs. They have a more pointed, slim line head compared to the Rock Monitor and the nostrils are positioned between the eyes and the tip of the head. They do have external ears that are diagonally down from the eyes towards the neck. The tail is noticeably longer than the body, and it is laterally compressed and a very effective defence mechanism. The tail normally has a banded pattern of a dark dirty brown and a lighter cream-beige colouration. The belly is normally paler than the body with some black bars. There are some blotches of yellow on the body, but it may be plain and the legs are often speckled with yellow. Juveniles are of similar patterning to the adults, except it is normally a lot clearer and more vivid. The main difference in juvenile colouration is that they are black & yellow. Juveniles are as aggressive as the adults and are quite willing to bite any threat. The teeth of juveniles are re-curved but in adults they become rounded and straight. Size of the Nile monitor

7 Advanced Snakes & Reptiles 7 Habitat: They are found along the coastal plains, Lowveld, bushveld, Highveld and the Karoo, but are always near permanent water, such as lakes, large rivers or dams in these areas. Diet: These reptiles are not fussy. As hatchlings and juveniles they will eat various insects like millipedes, locusts, beetles and even snails. They will also take small eggs if encountered. As an adult there is very little they do not eat. The will kill just about anything that can be swallowed. They will eat hatchling tortoises, any small mammals or rodents, fish, frogs, eggs of terrestrial birds like Guinea Fowl or Francolin, crabs, terrapins, and crocodile eggs or from raided nests of tortoises. Gender: There are hardly any noticeable differences between the sexes from a distance. Other than probing the animal it can sometimes be evident by looking at the base of the tail just below the cloaca. In males it is possible to see the long bulge of the hemipenes, where as in females the bulge is shorter and less noticeable. Habits: Nile Monitors on the whole are solitary animals, but they will sometimes occur in quite high densities. Monitors live in disused animal burrows, holes in trees or they will dig tunnels under rock ledges. They also hibernate and sometimes communally. On warmer days they will come out to bask and maybe look for some food. Normally they hibernate from April through to August / September.

8 Advanced Snakes & Reptiles 8 Reproduction: Copulation usually takes place soon after coming out of hibernation in privacy. Around two months after mating she will lay the eggs. Usually the female will dig a hole and lay the eggs in a termite mound. After laying the eggs the termites will repair the damage, leaving the eggs at a constant temperature and humidity to optimise hatching. They usually hatch the following season. Hatchlings are normally around mm in length. Neither the male nor the female protect the nest site. Banded mongoose often raids the nest of monitors. Nile Monitors are good powerful swimmers, relatively agile and quick moving on land, and are quite at home climbing trees. Nile Crocodiles, Southern African Pythons and more than likely raptors are usually are their main predators. Their main line of defence is to dive into the deep water and emerge elsewhere. If threatened on land away from water they will turn their bodies to the side facing the threat, curling the tail back and head fixed on the threat. As soon as the threat moves within the range of the tail they will lash out with an extremely powerful and painful blow on the recipient. If they are captured they will readily bite, use the tail and scratch, often causing deep painful wounds. If they do bite, they hang on and it is extremely difficult to get them off. Distribution: Distribution of the Nile monitor

9 Advanced Snakes & Reptiles 9 Rock Monitor Varanus albigularis albigularis Other Names: White throated monitor, Likkewaan, Leguaan or Rock Leguaan. Description: This is the smaller of the two species of varanid, but they are still large lizards that are extremely powerful. They have very strong legs and claws that are often used in defence, but aid in climbing and digging up nesting sites of other reptiles. They are not averse to trying to steal a few crocodile eggs. They have a more rounded or short stocky head compared to the Nile Monitor and the nostrils are fairly close to the eyes. They do have external ears that are diagonally down from the eyes towards the neck. The tail is often longer than the body, and it is laterally compressed and a very effective defence mechanism. The tail normally has a banded pattern of a dark dirty brown and a lighter cream-beige colouration. The belly is normally dirty mustard yellow in colour while the upper body and limbs are normally patterned or speckled in yellow. As their other common name would imply, they have white throats, but this is restricted to adults. Size of the Rock monitor Juveniles are of similar colouration to the adults, except it is normally a lot clearer and more vivid. The main difference in juvenile colouration is that they have black throats. Juveniles are as aggressive as the adults and are quite willing to bite any threat.

10 Advanced Snakes & Reptiles 10 Habitat: They are widespread through savannah, thornveld and bushveld. They also occur in the more moist areas of the Karoo. Diet: These reptiles are not fussy eaters. As hatchlings and juveniles they will eat various insects like millipedes, locusts, beetles and even snails. They will also take small eggs if encountered. As an adult there is very little they do not eat. T They will kill just about anything that can be swallowed. They will eat hatchling tortoises, any small mammals or rodents, eggs of terrestrial birds like Guinea Fowl or Francolin or from raided nests of tortoises and have been recorded eating Puff Adder. They will also go from predator to scavenger and eat carrion. Gender: There are hardly any noticeable differences between the sexes from a distance. Other than probing the animal it can sometimes be evident by looking at the base of the tail just below the cloaca. In males it is possible to see the long bulge of the hemipenes, where as in females the bulge is shorter and less noticeable. Habits: Rock Monitors on the whole are solitary animals, but they will sometimes occur in quite high densities. Monitors live in disused animal burrows, holes in trees or they will dig tunnels under rock ledges. They also hibernate, but on warmer days they will come out to bask and maybe look for some food. Normally they hibernate from April through to August / September.

11 Advanced Snakes & Reptiles 11 Reproduction: Copulation usually takes place soon after coming out of hibernation in privacy. Around two months after mating she will lay the eggs. Usually the female will dig a hole and lay the eggs, but they may occasionally lay them in termite mounds or hollows in trees. Incubation in captivity takes approximately 4 months at 27 o C - 28 o C, but is expected to take longer in the wild. Hatchlings are normally around 250mm in length. Neither the male nor the female protect the nest site. The banded mongoose often raids the nests of monitors. Rock monitors are good powerful swimmers, relatively agile and quick moving on land, and are quite at home climbing trees. They are preyed upon by large raptors such as the Black Eagle, but hatchlings will be preyed on by smaller raptors. In defence they will turn their bodies so the side faces the threat, curling the tail back and head fixed on the threat. As soon as the threat moves within the range of the tail they will lash out with an extremely powerful and painful blow on the recipient. If they are captured they will readily bite, use the tail and scratch, often causing deep painful wounds. If they do bite, they hang on and it is extremely difficult to get them off. In captivity it is normally quicker to submerge the animal under water, than to try and pry the jaws apart. As a last resort they will also sham death and hang limp. As soon as the grip is released they will flee. Distribution: Distribution of the Rock monitor

12 Advanced Snakes & Reptiles 12 Chameleons Order Squamata, Family Chameleonidae There are two species of chameleon that occur in this region. It is near to impossible to incorrectly identify a chameleon from any other lizard or confuse the two species. They are unique from lizards in that they have small, non-overlapping scales over the entire body, likewise the eyes move independently from each other. Lastly the four toes are opposite each other, almost giving an appearance of 2 fingers that grab or clasp onto branches. Unlike lizards the these species do not display autotomy and tail cannot be dropped or regenerated if injured and is quite often used when climbing in trees as a 5 th hand. These animals are almost strictly arboreal (tree dwelling), and will only move on land to get to other trees or the females to lay their eggs. The tongues are unique to the species in that they are long and used for hunting prey. As a rule of thumb the tongue can grab prey the same distance as the body length or more in some species. Most species are oviparous, and they lay soft-shelled eggs, similar to that of snakes. Chameleons are also solitary creatures and territorial. They do not accept the same or other sex within their range. Should any conflict arise between two chameleons they will often resolve disputes visually. They will change colours, inflate the throat poach, hiss and similar to look bigger and more aggressive than they actually are. Often this will resolve the conflict and very rarely will they engage in any combat. Chameleons have the ability to change their colouration to a degree to blend into their environment. As a rule of thumb the darker the chameleons colour the more stressed or aggressive it is. Alternatively the brighter they are, the more relaxed or aroused to a potential mate. Chameleons do not drink from ponds or streams. They will only "lick" dew, mist or rain off leaves. Chameleons are only insectivorous. There are two types of chameleons on the sub-continent. The main difference between Dwarf Chameleons and Common Chameleons is size and also common chameleons have diverticulate lungs, as opposed to simple lungs. There are 2 species that occur in the region: 1. Flap-Neck Chameleon - Chamaleo dilepis 2. Transvaal Dwarf Chameleon - Bradypodion transvaalensis

13 Advanced Snakes & Reptiles 13 Flap-neck Chameleon Chamaleo dilepis Description: Colouration of this species is varied. Not only because of their ability to change colours, but their colouration in a relaxed state. They can be green to brown to pale yellow. The flaps are more noticeable in the western populations. On the eastern extents they are very small and almost unnoticeable. The feet of the Flap Neck Chameleon are the same as all chameleons with the toes opposed allowing them to clasp onto branches. On the side of the chameleon are areas of white, normally a line but may be spots. They have a prehensile tail that cannot be shed or regenerated. The tail is often used as a 5 th hand when climbing. When sleeping, the tail is rolled up to form a coil. At night they are very easy to spot as they turn a pale white or yellow. Habitat: It prefers savannah, bushveld & thornveld, but does occur to the edges of coastal forests. Gender: Sexing of Chameleons is not the easiest task to undertake visually, especially as they are able to change from the normal relaxed colouration when agitated. Females have white interstitial skin on the throat, whereas males have orange skin. Other than this there is very little difference between the sexes. Diet: This species is only insectivorous, preferring beetles & grasshoppers but will also take crickets and other insects. Habits: This chameleon is arboreal and territorial.

14 Advanced Snakes & Reptiles 14 Reproduction: Combat between the same sexes and opposite sexes is common as they are extremely territorial. When the female permits approach of the male, there is very little foreplay. Despite this, copulation is fairly lengthy, lasting up to an hour. Soon as copulation is complete he moves off. The female lays between eggs at the base of a tree or damp soil about 3 months after copulation. Eggs will incubate for approximately a year before 4-5cm hatchlings emerge. Predation: Snakes such as the Boomslang, birds like the Fiscal Shrikes and Hornbills and even monkeys are predators of chameleons. When approached they normally turn dark in colour to almost black and inflate their bodies. Often they will hiss and inflate the throat pouch, displaying the interstitial skin. When highly agitated they raise the neck flaps and stand with the mouth open showing the white lining and will bite when in this position. They are needlessly feared even though some beliefs are that they are poisonous, they are in fact totally harmless. Distribution: Distribution of the Flap-necked chameleon

15 Advanced Snakes & Reptiles 15 Transvaal Dwarf Chameleon Bradypodion transvaalense Description: It is a relatively large Dwarf Chameleon, and it is the only Dwarf Chameleon in this area. The species is very distinctive from the Flap-Neck Chameleon by the tubercles present on the sides often in two rows. They have a fairly prominent cranial crest and a gular (throat) crest. The gular crest normally has 13 scaly flaps that get wider / broader towards the body, and begin to overlap each other. There can be between scaly flaps. The dorsal / spinal crest is also noticeable and extends down into the tail for about a third of the length. Adult colouration is varied and is described below. Hatchling and juveniles are of the same colouration as the females. This Dwarf Chameleon is endemic to Southern Africa and occurs along the escarpment. However in the future this one species may become a variety of subspecies or additional species. They are researching most of the species of Dwarf Chameleons to gain clarity on the species. It is possible that this Chameleon species could be divided into 7 or more new species or sub-species, as the research develops. For now though, there is only the Transvaal Dwarf Chameleon. Habitat: They are restricted to the escarpment forest or the forest fringes.

16 Advanced Snakes & Reptiles 16 Gender: Sexing of Chameleons is not the easiest task to undertake visually, especially as they are able to change from the normal relaxed colouration when agitated or aroused. Males have a pale yellow to mustard coloured band that goes from the side of the head to the side of the body, that can be edged in a maroon colour when they are in an aroused state. The throat region is cream in colour and their underside is rust or bronze coloured. Females are larger and are normally brown and cream in a mottled or speckled appearance. Vertical bars or blotches are common which extend from the back or spine towards the belly. The back or spinal region is often dark in colour and the sides have the cream coloured tubercles. The cranial crest is edged in a yellow to mustard yellow. Diet: This species is exclusively insectivorous. Habits: This chameleon is arboreal and territorial. They are normally restricted to small pockets in the distribution area and are not necessarily that common and certainly not easily spotted. Reproduction: Combat between the same sexes and opposite sexes is common as they are extremely territorial. During the breeding season the female may reject the males advances by facing him mouth agape and puffing herself up, also showing the colouration of her throat. Should he not retreat he will get bitten. The female has between 7-17 young during late winter or early spring. Snakes such as the Boomslang & birds like the Fiscal Shrike are the main predators of chameleons. The Transvaal Dwarf Chameleon is strictly diurnal.

17 Advanced Snakes & Reptiles 17 Distribution: Distribution of the Transvaal Dwarf Chameleon