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Crocodiles & Alligators

12 Temmuz 2007

Crocodiles & Alligators

Prehistory To The Present : Alligators , caimans , crocodiles and gharials are jointly referred to as crocodilians . The crocodilians are holdovers , survivors of that long-ago time known as the Age of Reptiles , a time when the dinosaurs were ruling creatures on the earth , dating from 265 million years ago to roughly 66 million years ago . The dinosaurs , the pterosaurs , and the crocodillians were known as Archesaurians and , even today , the crocodilians are refered to as saurins .

At the end of the Triassic period , about 210 million years ago , a small , slim reptile appeared which has been named Terrestrisuchus and is thought to be the direct ancestor of our modernday crocodilians . The terrestrisuchus , as its name implies , was primarily a land-dwelling reptile , running about on either two or four legs and feeding upon smaller lizards .

The ankle joints of these early reptiles are similar to present-day crocodilians . It’s one of the main links between them that these creatures could also either crawl slowly , bellies close to the ground , with the legs bent outward away from the body , or the legs could be straightened , lifting the body away from the ground and allowing the creature to run very rapidly for short distances . A creature known as Desmotosuchus also evolved that was very crocodilian in appearance and had evolutionary adaptations to a life in water , such as a vertically flattened tail for propulsion and a secondary palate that allowed them to seal their throat to prevent water from entering their lungs when they opened their mouth underwater . Both of these adaptations are present in today’s crocodilians .

By the end of the Jurrassic period , about 146 million years ago , the ancestors of present-day crocodilians had evolved , and although the direct lineage from the era to the present is not precisely established , both form and function were . It was also during the Jurassic period that the huge single continent , known as Pangaea , split apart to form the continents we know today . This continental drift caused some forms of crocodilians to become separeted . It also caused the great divergence , through isolation , into the many different species that we have today as each species evolved and adapted to the conditions in which each was found .

There is great speculation about the events that brought about the extinction of the dinosaurs . The one most favoured is that a huge asteriod hit the earth , sending up clouds of dust that enveloped the planet , blocking the sun , which killed the plants that the dinosaurs lived on . A second theory , that the beginning of an ice age killed of the dinosaurs , is not generally accepted because most of the dinosaurs died at about the same time . Another theory is that neither of these things happened , but the cooling of the earth was somehow speeded up . Since the dinosaurs were poikilothermic , or cool-blooded , a sudden drop in the temperature would not only have devastated their vegetative food supply , but greatly reduced their body functions and their ability to move . The crocodilians survived in part because they spend large part of their time in the water , which is more temperature-stable than air . There is also the possibility that many fish , which are the crocodilians main food source , survived by eating each other . There is also the probability that the crocodilians would have been able to hibernate , as our modern alligators do , during the winter months in the colder portions of its range , thus reducing their need for food for an extended period of time . Research indicated that a large crocodilian may be able to live for up to two years without eating . Climatic changes , such as the ice ages , shrank the ranges and greatly reduced the number of the species of crocodilians . They are now found only in the tropic and subtropic regions of the world . The populations of the remaining species were greatly reduced by a burgeoning human population , which led to competition for habitat and increased confrontation . A demand for the reptiles as food and their skins for leather led to the market hunting of many species . Many species were pushed to the brink of extinction . Some species survive today primarily in captivity . A growing awareness of their place in the web of the life has spawned new laws and regulations that have allowed many of these ancient reptiles to replenish their numbers in the wild . The American alligator has increased its numbers so dramatically that it had to be removed from the endangered species list and be harvested on a regulated basis in some areas .

Head And Eyes : All four forms of the crocodilians-alligators , caimans crocodiles and gharials basically resemble each other . The alligator has a broad , rounded , shovel-like snout while the gharial’s snout is long and very narrow . The snouts of the caimans and the crocodiles are between these two extremes , although a long , tapered snout is most common . All crocodilians have both their nose and their eyes located on the top of the skull so that they can see and breathe while the rest of their body is submerged beneath the water . Their eyes are set close together , giving them the binocular vision needed by all predators so they can accurately gauge the distance between themselves , and the prey they must capture .

By regulating the amount of air in the lungs , these saurians can float on the surface or sink below the surface with just their eyes and nose protruding above the water . The crocodilians have valvular , crescent-shaped nostrils that open when they breathe and close completely when they submerge . They have good hearing and their ears are covered with flaps to keep the water out .

Most of the species hunt prmarily at night and have vertical , cat-like pupils that open wide to allow more light to enter in low-light situations . Since they are night hunters , their eyes have a layer of tapetum at the rear of the eye which reflects whatever light is gathered back through the pupil , doubling their ability to see in the dark . Because of the tapetum , the eyes of crocodilians glows in the dark when a bright light is shined on them . The eyes each have a transparent nictitating membrane that covers it when they swim underwater .

Feeding : All of the crocodilians have powerful jaw muscles , to snap their jaws shut and to hold tightly to any struggling prey . The muscles to open the jaws are very weak and their mouth can easily be held shut . Their teeth are sharply conical , varying in lenght according to their placement , designed for grasping and tearing with small prey swallowed whole while larger prey is torn apart and the pieces swallowed . The teeth grow in sockets and are shed and replaced periodically . Some old alligators had as many as fifty sets of teeth .

Baby crocodilians feed heavily on insects and small fish , and then on larger prey as they become older , according to the species . In much the same way that birds use small stones in their gizzards to grind their food , large crocodilians swallow stones , called gastroliths , to help grind food in the stomach .

Like snakes , the crocodilians digestrive system is powerful enough to dissolve bones . When food is plentiful , these creatures store fat in their tails and body . This stored fat enables them to go for long periods without eating . As all crocodilians spend many hours each day immobile , their energy requirements are low .

Body Temperature : Alligators can live much farther north than any of the crocodiles because they have the ability to hibernate for periods of three to five months during extremely cold weather . They usually dig chambers in a river bank that are at least partly above the water , with underwater entrances . Some crocodiles will also dig such chambers , but they do so to escape from the heat of the summer . As mentioned , crocodilians are referred to as being ‘cold blooded’ when , in reality , their body temperature reflects the ambient air temperature or that of the nearby water .

These reptiles adjust their internal temperature by taking advantage of their surroundings . After hunting throughout the hours of darkness , the crocodilians crawl up on the sand bars or river banks as soon as the sun has dissipated the lower temperatures of the night . As the ait temperature is warmed by the sun , these reptiles will open their mouth in a wide gape . The evaporation of the moisture of the large mouth area lowers the temperature of the creature’s blood as it courses through the mouth . When the temperature becomes uncomfortably hot , the crocodilians will either seek the shade of nearby shrubbery or return to the water . Later in the day , when the heat has abated , they may crawl back up on the land until the cooling of the evening air sends them back to the water to seek prey of some sort .

In times of drought , crocodilians gather in whatever holes contain water . Alligators , too , are famous for the holes they dig , which teem with concentrated fish , birds , and gators during periods of low water . Usually , crocodilians get along well with each other , although smaller members will get out of the way of the larger ones . However , cannibalism does take place in some situations . Just recently , researchers saw larger alligators kill and eat two smaller 1.5 meter alligators in a pool near Gainesville , Florida . Over 212 alligators were concentrated in this pool because of drought .

Body And Movement : It was long believed that the crocodilians used their strong tails to sweep their prey off its feet and into the water . It is now known that most of the prey is caught after a silent , stealthy stalk and a startlingly swift attack . Mammalian prey is seized and pulled underwater to drown before being torn to pieces by the reptile . Some crocodilians can actually gallop for a short distance in pursuit of their prey on land . They have been known to jump as high as one meter horizontally and some larger ones can spring up vertically to a height of up to two meters .

The hind feet of the crocodilians are partially webbed , but their main propulsion , while swimming , is provided by their heavily muscled , vertically flattened tail . The tail is moved in an undulating S-shaped motion , driving the body forward at a speed that allows them to overtake swimming prey . While swimming , the front teeth are held parallel to the body , pointed to the rear , When crawling about on land , the tail is dragged along the ground , leaving a well defined trail . When a crocodilian runs on land , the tail is moved in the same S-shaped configuration used in swimming .

Fish , snakes , turtles , and even birds show their relationship to crocodilians through the scales on their bodies . Many of the reptiles shed their entire skin periodically as they outgrow it . The crocodilians shed individual scales . The skin of the crocodilians is heavily armoured over the top of the head , back and tail . When a crocodilian is taken for its hide , only the skin from its underside is used for leather because that section does not have the projecting , ridges scales known as osteoderms .

Crocodilians communicate through four scent glands and through auditory grunting and calling . The American alligator is the most vocal of all , with the young gators grunting while the adults , both male and female , bellow . The bellowing can be heard at anytime of the year , most frequently in April and May during the breeding season . The bellowing can be heard for a long distance and individual gators can be recognised by their bellow . Crocodiles and caimans may breed at any time of the years .

Reproduction : Depending on their habitat , some crocodilians scoop out a hole in the sand or dirt using their hind feet to lay their eggs . Alligators pile up mounds of vegetation using both their mouth and their feet . Anywhere from thirty to fifty leathery-shelled eggs are deposited in the hole , which are then covered with sand , dirt or vegetation . The sun provides the heat need to incubate the eggs , with the rotting vegetation providing additional heat . The hatching time is greatly influenced by the ambient temperature , but most hatch within two to three months .

Alligators and some crocodiles stay in the vicinity of the nests to protect them from such predators as raccoons , bears , wild pigs , monitor lizards , and goannas . An interesting phenomenon was recently discovered in research on alligators . It was found that when the eggs were incubated bellow 32C (90F) mostly females developed . Above 33.5C (92F) more males were produced whereas , if the temperature was between 32C and 33.5C , both sexes would be produced about equally . This phenomenon is called temperature-dependent sex determination , or TSD . Research with other crocodilians as well as with sea turtles , shows that they are affected also , but at slightly different temperatures and with different results according to the species .

In order to escape from the leathery eggshell , baby crocodilians are equipped with a projection of skin known as an ‘egg tooth’ . This is similar to the egg tooth falls off on the third day while the crocodilians egg tooth is reabsorbed on about the fifth day . The young crocodilians are strong enough to dig their way through the protective layers of sand , dirt and vegetation .

In alligators there is evidence that the female is summoned by the babies grunting and that she assists them by digging open the top of the nest . Both crocodile and alligator mothers have been seen carrying their young to water in their mouth . The young crocodilians are preyed upon by all of the above mentioned predators as well as by snakes , fish , herons and vultures .

Upon hatching , the babies are 19 to 25 Cm (8-10inches) in length and grow at the rate of almost 30 Cm a year until the age of five . They will continue to grow all of their livs , but slow down progressively from then on . The lenght each species may attain is given in the account of that species .

Alligators And Caimans :

The American Alligators

The American alligator , Alligator mississippiensis , is found from South Carolina to north-eastern Mexico along the coastal regions and as far up the Mississippi River as Arkansas . Its range has been greatly diminished by the draining of both coastal and inland swamps and marshes when these areas were converted to farmland . Their numbers were decreased by market hunting and then further reduced by poaching in the 1950s and 1960s . The alligator was then considered endangered , but has recovered to the point where Louisiana estimates there are at least 380,000 of these big reptiles in that state alone . A hunting season had to be reinstated to prevent the overpopulation of alligators and the total destruction of the valued furbearers such as the muskrat , otter , and nutria .

The alligator feeds mainly upon fish and it has decided preferences as to which kind of fish it will eat . It feeds heavily upon many species of garfish , but will not eat the long-nosed garfish . It has very broad tastes , though , and will readily feed upon any birds , snakes , frogs , turtles , crabs , or small mammals that it can catch . They have been known to catch and eat animals as large as a deer . The largest alligator there is an authentic record of was the giant called “Old Monsurat” , killed by E. A. McIlheny of Tabasco fame on his Avery Island , Louisiana , estate in 1890 . The huge gator measured 5.6 meters (19 feet 2 inches) , but it was not weighed . It could conceivably have weighed in the 202 to 225 kilograms (450-500 pounds) range . There are a number of records of alligators in the 4.8 to 5.1 metre (16-17 foot) class .

I estimated that the largest alligator that I have personally seen was 4.5 meters (15 feet) in length with a probable weight of 160 kilograms (350 pounds) . I saw this alligator in the Aransas Wildlife Refuge on the Texas coast and the refuge biologist said he thought my estimate was about right . Alligators have been accredited with great longevity , but research has found that most of those over fifty years old have lost most or all of their teeth , so they would have great difficulty in obtaining prey species and would gradually die of malnutrition . In fact , McIlhenny was convinced that the huge gator he shot in 1890 was dying as it was practically toothless .

As the American alligator population has grown since the 1970s , and the areas the gators live in have been invaded by a burgeoning human population , conflict was inevitable . What has made the problem worse is that many people began to feed the gators , which not only attracted them but kept them in the area . Rather than shy and retiring , as a truly wild alligator is , the ones that are fed become very aggressive . Attacks on people are now fairly commonplace . Many pet dogs are eaten by the gators . The gators have to be removed from boat docks and from swimming pools . The ponds and lakes on golf courses are known as “water hazards” and many of them are now truly hazardous because alligators have taken up residence there .

The Chinese Alligators

The Chinese alligator , Alligator Sinensis , is believed to be the progenitor of the mythical dragon of Chinese art , literature , and religion . The alligator was first mentioned in Chinese literature in the third century AD . In his book on his travels , published in 1299 , Marco Polo describes an encounter with what surely must have been this alligator while he was in China .

No one is sure just how extensive the range of this alligator was in the years gone by . Although it is mentioned in Korean literature , the waters are too cold and the rivers too swift and turbulent for this reptile . The range of this alligator today is along the banks and marshes of the Yangtze River in the area of Yueyang , Wuhan , and Nanchang . This area is on the 30th parallel , giving the Chinese alligator about the same range northward as the American alligator .

Like the American alligator , its Chinese counterpart will hibernate during the cold winter months by submerging itself in a tunnel in the riverbank . Made lethargic by the cold , many of these alligators drowned in their burrows in 1987 when the Yangtze flooded in the winter . It is estimated that there are perhaps no more than three hundred Chinese alligators alive in the wild . Captive breeding programs in zoos and research stations throughout the world are helping to keep the species alive . Although there are reports of these alligators growing to a length of 3 meters (10 feet) , a really one today is 2 meters (6.6 feet) .

One favorable point for this alligator is that its hide is not desired for leather because of osteoderms on its belly . However , the Chinese attribute medical cures to different parts of its body , such as its gall bladder , and they also relish its meat .

This is a very shy , retiring species and there are no records of it ever attacking a person . It has been known to take villagersÂ’ dogs and chickens . It feeds primarily upon fish , frogs , and turtles .

The Common Caiman

The common caiman , Caiman crocodilus , is perhaps better known as the spectacled caiman , a name suggested by the bony ridges and light coloration encircling its eyes . It has a large range , being found from southern Mexico through Central America and on down through the heartland of South AmericaÂ’s Amazon basin . There are no accurate figures on its total population , but it is estimated that there are at least four million of this species in just Venezuela . Years ago , baby spectacled caimans were a hot selling item in pet stores . Records of some 3-metre (10-foot) specimens exist , but any spectacled caiman that reaches a size of 2.5 meters (8 feet) is considered to be a big one . It is hunted for its skin , despite having some osteoderms on its belly . Apparently none of the native people eat the spectacles caiman . If this caiman is exposed to cold weather , it changes color from a basic greenish yellow to brown . In the brown stage , even the southern subspecies resembles the most northern subspecies , which is known as the brown caiman . The breeding season for this common caiman occurs in August at the tail end of the dry season . This is advantageous to the species because , by the time the eggs hatch out in November , the waterholes , swamps , and savannahs will be filled with water and teeming with aquatic life . The spectacled caiman is unique in that the females often nest communally , with two or more females laying their eggs in the same mound . this has the decided advantage of giving the nests greater protection , with two or more guardians . In spite of this increased protection , as many as 80 percent of the nests may be opened and the eggs eaten by the large monitor-type lizard known as the tagu . Despite the fact that this caiman is common throughout so much of a large range , very little is known about its eating habits . It is known that it feeds upon fish , small invertebrates , and small animals . Although they are found in ranching areas , they have not been known to eat livestock .

The Broad-Snouted Caiman

The broad- snouted caiman, Caiman latirosteris , is found in southeastern Brazil , Paraguay , Uruguay , and Argentina . It can be recognized by its broad snout and by the ridge that runs the length of the snout . This caiman closely resembles the American alligator in appearance , but not in size . A really big individual may attain a length of 1.8 meters (6 feet) , but this is rare . It is a very shy creature and usually inhabits areas with dense floating vegetation , making it extremely difficult to see . They are basically aquatic and usually hunt at night . They feed mainly upon snails and crabs , as well as many types of aquatic invertebrates . It is thought that their broad jaws are an adaptation to allow them to crush the shells of the turtles they feed upon . They are the southernmost species of caimans and , as such , are exposed to colder weather than are their more northern relatives . Their dark coloration helps them to absorb and to hold more warmth from the sun even on cold days . Although they are more cold tolerant than are other caimans , they spend less time basking on the riverbanks and more time in the water .

Unfortunately for the survival of this caiman species , its skin makes especially fine leather and is much in demand . Hunting has greatly reduced its population . In addition , it is believed that many of these caimans may be dying from parasitic flukes that they pick up by eating the snails that their hosts discard .

The male broad-snouted caiman helps the female dig the nest , helps to guard the eggs , and has been seen carrying the hatchlings to the water in his mouth . There does not appear to be any concentrated effort to prevent the depletion of this species .

The Black Caiman

The black caiman , Melanosuchus niger , is concentrated in the Amazon River basin , Guyana , and French Guiana . It is the largest crocodilian in South America . Really large ones can reach a length of over 6 meters (20 feet) . The black caiman has been in great demand for its skin , and market hunting has reduced both its population and range by about 99 percent . In the early 1970s , as many as 66,000 hides were shipped out of Colombia alone . Today , this caiman is virtually extinct in that country .

The young black caiman feeds heavily upon shrimp and crabs , snails , and fish . AS they grow larger , they tend to feed more upon mammals , such as the capybara , the worldÂ’s largest rodent , as well as on deer . Fish are still an important item in an adultÂ’s diet , as are turtles . Black caimans have especially good hearing and often home in on their prey , in the darkness , by detecting whatever sounds the prey makes .They eat domesticated animals and , occasionally , one will attack a human . The attack on humans is a comparatively rare event .

In December , drought conditions concentrate fish in shallow pools , creating an almost unlimited food supply for the caimans . This allows the female to be in excellent condition when she does her egg laying and they lay between fifty and sixty-five eggs . The nest is about 1.5 meters (5 feet) across and up to .75 meters (1 ½ feet) high , made of piled vegetation .

As they are very tolerant of each other , a number of females will often build their nests in a very small area . With a number of females in a small area , predation is kept to a minimum . The black caiman is in direct competition for some food resources with the spectacled caiman , whose range it overlaps and which is much more numerous . The tremendous reduction in the number of black caimans has had a deleterious effect upon the environment . Both the piranha fish and the capybara populations , black caiman food staples , have increased dramatically as the black caiman population has declined . The capybaras are destroying agricultural crops and piranha are attacking more cattle .

The Dwarf Caiman

The CuvierÂ’s dwarf caiman , Paleosuchus palpebrosus , has the thickest skin of any of the crocodilians . They are also the smallest in size of any of the New World crocodilians , with a big male reaching perhaps 1.5 meters (5 feet) while the female grows to 1.2 meters (4 feet) or less . It is thought that these caiman might have thicker armour as added protection due to their small size , but it may also be selective adaptation to protect them from being cut when thrown against sharp rocks in the fast-flowing water in which they often live . I tend to believe the former hypothesis because these caiman spend a lot of their time in still waters and they also spend much time on land looking for food . Those that live in still water frequently have filamentous algae growing on them . This provides them with an even better camouflage .

These caiman are found in Brazil , French Guiana , Suriname , and Venezuela . The CuvierÂ’s caiman feeds heavily on fish , but also takes shrimp , crabs , frogs , toads , snakes , birds , and small mammals . CuvierÂ’s caiman are shy and usually solitary . They have never been populous and no one really knows how many there are . They are not sought for their hides . The female builds her nest out of vegetation , then adds mud to finish the heap . The nest is usually further hidden under some dense vegetation and is seldom hit directly by the sun . Because the ambient temperature is never as warm as the sunÂ’s rays , it takes up to ninety days for the twenty to twenty-five eggs to hatch . The female stays in close attendance to the nest to guard it from predators and to open the mud-hardened structure when the young break out of their shells .

The SchneiderÂ’s dwarf caiman , Paleosuchus trigonatus , is frequently called the smooth-fronted caiman because the skull lacks the bony ridge between the eyes .Both CuvierÂ’s and SchneiderÂ’s caimans have a bony flap that comes down , completely protecting the eye , when the upper eyelid is lowered . Like the CuvierÂ’s caiman , the SchneiderÂ’s caiman is also very reclusive , coming out only under the cover of darkness . They spend the daytime hours hidden in tunnels they excavate in the riverbanks .

This species of caiman prefers to live in fast-flowing or turbulent water . Their diet is mainly fish , with a large number of those being different kinds of catfish . They have also been known eat snakes , shrimps , crabs , and snails . They occasionally hunt on land for birds and small rodents . One of these caiman , 1.8 meters (6 feet) in length , was eaten by an anaconda that measured 5.9 meters (19 ½ feet) long , Some of these huge snakes have measured up to 10.5 meters (35 feet) in length and many of them prey upon the smaller crocodiles .

A large male Schneider’s caiman may measure up to 1.7 meters (5 ½ feet) in length while a large female may measure 1.4 meters (4 ½ feet) .

The SchneiderÂ’s dwarf caiman is not hunted for its hide because its belly is also covered with osteoderms , rendering it unfit for leather . The ventral osteoderms do provide this caiman with a complete set of armor . The nest is constructed by the female out of vegetation . The female then lays a clutch of between twelve and fifteen eggs . AS with the CuvierÂ’s caiman , it takes almost three months for their eggs to hatch .

American And African Crocodiles :

The American Crocodiles

Because it has the largest range of the four New World crocodiles , the American crocodiles , Crocodylus acutus , is perhaps the best known . In North America , its range is restricted to the brackish regions of the Florida Keys , although it goes up fresh water canals around the Everglades . It is found on islands in the Caribbean , Mexico , Central America , Colombia , Venezuela , Ecuador , and Peru . A distinguishing feature of all of the crocodiles is that the fourth tooth , on either side of the lower jaw , is so long it protrudes through holes in the upper jaw . The American crocodile can further be distinguished from all other crocodiles because it has less bumpy osteoderms on its back . It is extremely rare to find any specimens of this crocodile today that measure over 4 meters (13 ½ feet) in length . There are authentic records from years ago of some that were 7 metres (21 ½ feet) in length .

All crocodiles have a gland in their mouth that allows them to extract and eject salt from saltwater so it can be drunk . This gland is more efficient in some species than in others . The glands of the American crocodile are among the less efficient and even the adults prefer to drink fresh water while their young must have access to fresh water in order to survive .

American crocodiles frequently dig tunnels to which they retire , not as a protection against the cold but as a refuge from the heat , during periods of drought . This is known as aestivation . Like alligators , the American crocodile will lumber up on land in the early morning to warm up and then retire to the water in the midday to cool off . The crocodiles feed primarily at night . While young , they eat mainly small fish and some small vertebrates . The adult crocs feed mainly upon fish , turtles , snakes , small mammals , and small domestic livestock . Attacks on man have occurred but are rare . American crocodiles seldom make a nesting mound . In the swampy areas where they live , the females , like turtles , use their hind feet to excavate a hole in the soft peat . She lays between forty and sixty eggs that measure 7.5 centimeters (3 inches) in length by 5 centimeters (2 inches) in width . The female will then make a tunnel for herself in the immediate vicinity so that she can guard against any predators . After a three-month incubation period , she will help the young to hatch by opening the nest .

The populations of this crocodile have greatly declined not only because it was hunted for its skin , but because dams and canals diverted so much that the salt content of bays and estuaries is too high for the young to survive .

Caribbean Crocodiles

The Morelet’s crocodile , Crocodylus moreletti , is found only on the Caribbean side of Central America . It is small as crocodiles go , with a really big one measuring up to 3.5 meters (11 ½ feet) in length . Most of the big ones are in the 2-meter (about 7-foot) class . The coloration of this crocodile is a dull greyish brown , which helps it to blend in with the dense floating vegetation of the freshwater ponds and lakes that it frequents . In these areas , they feed upon snails , turtles , fish , and small mammals . The young eat many invertebrates .

Because these crocodiles lack osteoderms on their belly , their hides have been in great demand and market hunting has brought them to the verge of extinction over much of their range . Fortunately , they do breed well in captivity and Mexico is doing a fine job of captive rearing and releasing of the young crocs in the Yucatan area in an effort to prevent their extinction . Also , most of the countries where they are found have improved enforcement of the protection that the crocodile needs is it is to survive .

The female MoreletÂ’s crocodile will build a substantial mound of vegetation as a nest in which she will lay between twenty and forty-five eggs . It takes about eighty days for the eggs to hatch . The mother will be in the vicinity to prevent predation and she is sometimes joined by the male in caring for the hatchlings .

The survival of the Cuban crocodile , Crocodylus rhombifer , is seriously threatened because this species has the most restricted range of any of the crocodiles . It is found in only two swamps in Cuba . While formerly the American and Cuban crocodiles inhabited different ranges , the destruction of much of their natural habitat has forced two species into the same areas . The Cuban crocodile has never been as numerous as its American counterpart and the two species are now hybridising to the detriment of the Cuban species . It is conceivable that , within a few years , the Cuban crocodile could be bred out of existence . The Cuban crocodile has a much shorter and more broad head and is more yellow in coloration than the American , with the hybrid offspring often showing characteristics of both species . However , since the American is much more numerous , the Cuban characteristics will probably be completely subverted through time .

Today the Cuban crocodile feeds mainly upon fish and turtles , its large , flattened rear teeth crushing the turtleÂ’s shell very easily . The high walk of the Cuban crocodile shows that in the past than it does today . Then those large rear teeth would have been used for crushing bone . Very little is known about the nest and egg laying of the Cuban crocodiles pile up vegetation for a nest , it is probably safe to assume that this one does also . The eggs are 7.5 centimeters (3 inches) in length by 5 centimeters (2 inches) in diameter .

The Orinoco Crocodiles

He Orinoco crocodile , Crocodylus intermedius , inhabits only the Orinoco River drainage basin in Venezuela and the Meta River drainage basin in Colombia . It is a large crocodile , measuring 5 meters (16 ½ feet) or more with somewhat questionable records of 7 meters (22 feet) from the “good old days” not uncommon .

Because the crocodile has no osteoderms on its belly , and is large in size , its hide was in great demand for leather . In the heyday of the market hunter , from 1925 to 1935 , fortunes were made and hundreds of thousands of these crocodiles were killed . Today they are given a measure of protection and it is no longer feasible to hunt them . It is estimated that there are less than fifteen hundred of this species left in the wild .

The female digs a hole on a riverbank that is above the flood-stage level . Here she deposits thirty to forty eggs and covers them up . She takes up a sentry post a short distance away to ward off such predators as the terid lizards and black vultures . After two months or so , the eggs hatch . The hatchlings feed mainly upon beetles , snails , crabs , and invertebrates . Its long , narrow sout is indicative of its diet of fish . The adults feed mainly upon fish , birds , and the capybara . These big rodents often weigh up to one hundred pounds and provide a good food source . There are no authenticated reports of this crocodile attacking humans .

During periods of flooding , this crocodile leaves the Orinoco River and travels overland to nearby quiet lakes and ponds . AS the waters recede after the rainy season , the crocs go back to the deeper river . There are records of this crocodile being swept out to sea on masses of vegetation during the high flood period and ending up on the offshore islands of Trinidad and Grenada .

Nile Crocodiles

I have seen the Nile crocodile , Crocodylus niloticus , stacked up like cordwood on the riverbank below MurchisonÂ’s Falls in Uganda . These crocodiles were guarded carefully by the wardens of the park . Elsewhere , their population has been greatly reduced by market hunting , with three million hides being taken between 1950 and 1980 . In some other areas , such as Lake Turkana in Kenya , many of the crocs are trapped and drown in fishermenÂ’s gill nets .

In Natal , so much water has been removed from Lake St. Lucia for agricultural irrigation and the lake has become so saline that the crocodiles are dying . While no one wants to see a species exterminated , the native people are very glad to see the population of this crocodile greatly diminished . The Nile crocodile is a fearsome man-eater and it is estimated that it kills about three hundred people per year, even today . The native women wash their clothes by sitting in the rivers , often facing the bank , and usually don’t see the crocodile that takes them . It is a large crocodiles , with many being over 5 meters (16 ½ feet) in length . In 1905 a monster Nile crocodile 6.5 meters (21 feet) and weighed about 1035 kilogrammes (2,300 pounds) . A more recent leviathan taken in 1953 in Uganda measured 5.9 meters (19 ½ feet) in length and more than 2 meters (6.6 feet) in heart girth .

While photographing the crocodiles at MurchisonÂ’s Falls , a rope accidentally became entangled around our launchÂ’s propeller . One of the natives dove overboard and cut the propeller free . There is no way that I would have volunteered for that job with all those toothy denizens piled up on the bank . I will ad that not one of the crocs even stirred to enter the water . During Idi aminÂ’s fearsome rule of Uganda in the 1970s , he disposed of the bodies of his political enemies by feeding them to the MurchisonÂ’s crocodiles .

The adult crocodiles lie in the water and wait for prey species to come and drink . Then , with a sudden lunge , amid a cascade of water spring forward to grasp the prey and pull it into the water to drown . They will take birds of any and all sizes and animals up to the size of a horse or giraffe . I have seen where the crocs had killed so many wildebeests , at the Mara River crossing in Kenya , that they couldnÂ’t eat them all .

Despite the taking of birds as prey , a symbiotic relationship has developed between the crocodiles and the African spur-winged plover and the thicknee . This was first written up by Herodotus almost 2500 years ago . He wrote that as the Nile crocodile lay with its mouth open, these two species of birds would pick leeches and food particles from between the teeth of the crocodile . This came to be regarded as a myth because so much of what this Greek historian wrote proved to be groundless . However , this comensal relationship has been documented by modern-day researchers . This crocodileÂ’s nest is an excavated hole dug in a riverbank or sandbar above the high-water level . Fifty to sixty eggs may be laid and the nest will be guarded by the female and sometimes by the male as well . I have seen 1.5-meter (5 foot) monitor lizards in the same vicinity as these huge saurians , but have not witnessed them digging up the eggs . The Nile crocodile is found throughout most of Africa except for the northwest desert and the southern mountain areas .

The African Caimans

The African slender-snouted caiman , Crocodylus cataphractus , is a little-known crocodile , usually solitary and very shy . It does little or no basking and inhabits a deep jungle environment so that it is seldom seen . It is found in all of the West African countries bordering the Atlantic Ocean from Senegal south to Angola . It prefers the quiet waters of slow-flowing rivers , lakes , and ponds . They average 2.5 meters (8 feet) in length , with a really big one being half again as large . Their long, slender snout and body fit their aquatic life and they feed heavily upon small mammals and birds . At egg-laying time , the female piles up a nest of vegetation , mainly forest tree leaves , on the edge of e riverbank . She lays a small clutches of eggs , averaging sixteen . This small clutch size shows that these crocodiles are subject to little predation because each species lays eggs enough to keep their population stable . She will help the young to get out the nest when they hatch and grunt to call her .

The African Dwarf Caimans

There is scientific disagreement as to whether the West Africa dwarf crocodile , Osteolaemus tetraspis , is one species or if it should be broken down into two species . This species is found in Sierre Leone , Guinea , Ghana , Togo , Nigeria , Cameroon , and Gabon . A second species , or subspecies , has been dubbed the Congo dwarf crocodile , Osteoblepharon osborni .

These crocodiles are distinguished by their small size of about 1.5 meters (5 feet) . There are records of some that have reached a length of 1.8 meters (6 feet) , but that is exceedingly rare . Another characteristic is the crocodileÂ’s upturned nose .

Their small size makes them inoffensive to man and their ventral osteoderms make their hides unfit for leather , so they have been relatively unmolested . They are fresh-water crocodiles and are found in the rivers , ponds , and lakes of the jungle region . Not a great deal is known of their habits and , although their diet is primarily fish , it is believed that they secure some of their food on land , as do the monitors and iguanas . They seldom bask on riverbanks or sandbars and are not really seen that often as they are most active under the cover of darkness . It is known that , when they are disturbed , they will seek refuge in tunnels that they dig in riverbanks .

The nest is a mound of vegetation piled up by the female in which she deposits her ten to fifteen eggs . She guards the nest against predators for the three months that it takes the eggs to hatch .

Indo-Pacific Crocodiles :

The Saltwater Crocodiles

The Indo-Pacific or saltwater crocodile , Croccodylus porosus , is the largest and most fearsome of all of the crocodilians . One killed in AustraliaÂ’s Northwest Terrtory in June 1960 measured 6.15 meters (20 feet , 2 inches) in length . In 1962 , another one of these crocodiles was killed in the Territory that measured just 6 meters (20 feet) , but weighed an incredible 1088 kilogrammes (2,418 pounds) . The largest crocodile reported was not killed , but the sandbar on which it tested was measured by James Montgomery on the Segama River in Borneo in the 1920s . It was estimated that the crocodile was 10 meters (33 feet) long . A crocodile now living in the Bhitarnika Sanctuary in Orissa , India , is estimated to be 7 meters (23 feet) in length .

The Indo-Pacific crocodile inhabits an area encompassing the lower tip of India to be Philippines , all of Indonesia and surrounding islands , and northern Australia . In that vast territory , it is estimated that this crocodile kills at least one thousand people each year . The greatest carnage done by these crocodiles occurred toward the end of World War II . The British , in retaking Burma , had pushed a force of over one thousand Japanese soldiers to the coast . The Japanese had expected to be picked up by one of their ships and evacuated . However , because of British ships patrolling just off the coast , the Japanese soldiers fled into a large mangrove swamp between Burma and Romree Island . During the night Indo-Pacific crocodiles attacked and , by morning , only twenty Japanese were still alive .

The Indo-Pacific crocodile feeds upon fish but , like the Nile crocodile , it can catch mammals up to the size of water buffaloes . It stealthily sneaks closer and closer until , within striking distance , it charges out of the water , grasps its prey , and pulls it into the water to drown . This crocodile is also called the saltwater crocodile because it is found primarily in saltwater or brackish areas . Its salt glands are well developed and it can ingest saltwater with no harmful effects . However , this crocodile will travel many kilometers up freshwater rivers and streams . The one I encountered in Australia was about 48 kilometers (30 miles) up the Alligator River from the ocean .

In keeping with their large size , these crocs make a nest that may be 2.5 meters (8 feet) across and 91 centimeters (3 feet) in height . The nest is made of piled-up vegetation liberally mixed with mud . AS many as ninety eggs have been found in one nest . Incubation takes three months , with the female guarding against predators . Due to the mud hardening , the female is needed to help the young escape from the nest .

The Mugger Crocodiles

The mugger crocodile , Crocodylus palustris , is the sacred crocodile of India . It is found in India , Nepal , Pakistan , Iran , and Sri Lanka . Most males will average 1.8 to 2.4 meters (6-8 feet) in length with really big ones reaching 4 meters (13 feet) .

The mugger has the same broad snout as the alligators . It , too , is a marsh-dwelling creature . In fact the “palustris” in its name means “of the marshes” . It prefers fresh water but occasionally will be found in estuaries . Like the alligator , the mugger is an opportunistic feeder , eating mainly fish but also eating any turtles , snakes , birds , and small mammals that it can find . It does not attack man . The human birthrate of the area in which the mugger is found is very high and , as the human population increases , all types of wildlife , the mugger included , are greatly reduced . Captive breeding programmes are under way in several of the countries involved in an effort to prevent the loss of that species .

The nest is simply a hole dug in a riverbank by the female in the months of February and March . Thirty eggs comprise the average clutch , which takes about sixty-five days to hatch .

The New Guinea Crocodile

The New Guinea crocodile , Croccodylus noureguineae , was not confirmed as a distinct species until 1938 . New Guinea has a high mountain range running lengthwise through the island and this mountain has separated this species into two subspecies . As this crocodile is a freshwater species , it will not swim around the landmass and no interbreeding between the north/south subspecies is known to occur . This crocodile grows to a length of 4 meters (13 feet) . They have been hunted extensively for their hides so that their population is greatly reduced .

This species prefers the spacious swamplands found at the lower elevations . In times of drought , these crocodiles will seek refuge in the deeper rivers . They are seldom seen because they are almost strictly nocturnal . It is known that it feds upon fish , amphibians , reptiles , and water birds . Being a very shy creature , it is not a threat to man .

The nest is a mound of vegetation piled up at he edge of the dense jungle just high enough above the water to be above flood stage . Their nests have also been found built up on floating mats of vegetations . The female lays about thirty eggs and stays in the vicinity to guard the nest . Being shy , she will not defend the nest if a man appears . The young hatch in a period of twelve weeks , with both the male and the female taking the hatchlings to water . Although the adults are seldom seen basking , the young need the warmth of the sun and spend considerable time lying in the sunshine . This is important because , as the sun raises the baby crocodileÂ’s body temperature , it stimulates the baby to feed .

The Johnston’s Crocodiles

The JohnstonÂ’s crocodile , Crocodylus johnstoni , is better known as the Australian fresh water crocodile . AS the Indo-Pacific saltwater crocodile is frequently found kilometers from the coast , living in fresh water , the JohnstonÂ’s crocodile can sometimes be found in brackish estuarine areas . It is found across the northern edge of Australia . Its long , tapered nose shows that it is primarily aquatic , feeding mainly upon fish , amphibians , turtles , and occasionally birds and small mammals . Although it grows to length of 3 meters (10 feet) , it is not aggressive toward man . In some areas there are dwarf populations of this crocodile . It is believed that it is the periodic shortage of food during the drought season that has produced these smaller crocodiles as an adaptation . Quite logically , the crocodiles become smaller the closer you get to the headwaters of any of the rivers . As there is a lessening of food , there is a lessening of crocodilian growth .

The females do not build a mound as a nest , but simply dig a hole in the riverbank . Often a large number of females will nest in one general area . This could result from a lack of suitable nesting sites as much as from sociability . The clutches are small , with twelve to eighteen eggs being the norm . The eggs hatch in about three months . Although the eggs are often preyed upon by monitor lizards , the female is not a particularly good guardian .

The Philippine Crocodiles

The Philippine crocodile , Crocodylus mindorensis , is an exceedingly rare species . Whereas it was formerly found on a number of the Philippine Islands , the remnant population , believed to be less than five hundred individuals , is now centered on the island of Mindanao and the Sulu Archipelago . The combination of overhunting for its skins and destruction and drainage of its habitat for agriculture has severely endangered this species . There are several captive-breeding programmes under way at the present time in a concerted effort to prevent the extinction of this crocodile . Although the Philippine crocodile attains a length of up to 3 meters (10 feet) , it is shy and not aggressive toward man . These are mound-building crocodiles , with the female piling up vegetation . Again , the clutches are small , with ten to twelve eggs being the average . The small clutch size also is a deterrent to rapid population growth . Incubation of the eggs takes twelve weeks , with the female in constant attendance . This is a freshwater species , found in both the rivers and lakes , where it feeds mainly upon fish . Occasional birds and small mammals are also taken .

The Siamese Crocodile

The Siamese crocodile , Crocodylus siamensis , is another crocodile on the verge of extinction in the wild , primarily because it was hunted so heavily for its hide . This crocodile also suffers the disadvantage of looking so much like the Indo-Pacific crocodile that it was killed because it was mistaken for the latter . While the Siamese crocodile is not aggressive toward man and the Indo-Pacific crocodile is , to most people “a crocodile is a crocodile” and the relatively harmless Siamese crocs were killed out of fear of the latter species .

At one time this crocodile , which lives primarily in fresh water but also occasionally in brackish water , the same habitat as the Indo-Pacific crocodile , was found in Vietnam , Cambodia , Thailand , Laos , and the Malay Peninsula . Today , the only wild population , which numbers about fifty individuals , is found at a reservo9ir in the Nakhon Province in Thailand .

The female lays her twenty to forty eggs in a mound of vegetation . She guards the eggs during the eleven-week incubation period and helps the hatchlings to emerge from the nest . The young feed upon aquatic insects and small fish . The adults feed mainly upon fish , supplementing their diet with whatever waterfowl and small mammals that they can capture .

The False Ghariale

The false gharial , Tomistoma schlegelii , is a freshwater crocodile that has the long , very thin snout of the gharial , this crocodile has a snout body . It grows to a length of about 1.8 meters (6 feet) and is harmless to man . The false gharial is an endangered species , with a few wild populations found only on the Malay Peninsula , Sumatra , and Borneo . The loss of habitat is the prime reason for the reduction in the numbers of this crocodile .

The fact that , after the female lays her eggs in a mound of vegetation , she does not guard them leaves the nest subject to heavy predation . Feral hogs and even those kept under domestication by the locals wreak havoc on the nests and , if discovered , all fifty to sixty eggs will be eaten .

The Gharials

The gharial , or gavial , Gavialis gangeticus , is a crocodilian , but it is the only species in its own family . As its Latin name reveals , the gharial is a creature of the Ganges , Chambal , and Brahmaputra rivers in India and the Rapti-Narayani River in Nepal .The gharial cannot be mistaken for any of the other crocodilians due to its long , slim body , extremely long , thin snout , and its sharply rear-curving teeth .

They do grow to a large size , with one being shot that measured 6.5 meters (21 feet) . They feed almost exclusively upon fish and their thinness in both snout and body allows them to move very quickly through the water . The thin snout is often is often swung sideways , like a scythe , through the water .

It is not known if the female makes a mound nest or , as is more commonly suspected , digs a hole in the sand . Captive females gave been known to lay about forty eggs . The gharials do not attack humans . They have been hunted for the leathered market and their eggs are often used for food by the natives . Unfortunately , much of the Asian pharmacopoeia is based on using various parts of wild creatures . Parts of gharial snouts are supposed to have aphrodisiac qualities . India has a high birth rate . Much destruction of habitat accompanies a human population explosion , and the gharials have suffered because of this . Captive breeding programs are under way to save this species from extinction .

Credit :

By ; Murat Tarhan

Copyright © 2002

Kategori: Biyoloji