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> American Crocodile
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American crocodiles are giant, semi-aquatic reptiles directly descended from ancient crocodilians that were alive before the dinosaurs. They are intelligent and adaptable animals. According to scientists, crocodiles' 60-year life spans and complex social relations indicate that they could be highly intelligent. Their brains are only about the size of a cigar, but they seem to quickly recognize patterns, and they respond to recurring situations with new behaviors. Crocodile wranglers claim that it is difficult to catch the same crocodile in the same trap twice.
Crocodiles are unlike other reptiles: they have a four-chambered heart
like birds and mammals.
American crocs live in the brackish waters of coastal wetlands, mangrove swamps, and the estuaries of freshwater rivers--never more than a thousand feet above sea level. Adults venture out to sea, but juveniles, which cannot swim at birth, are sensitive to saltwater and must be reared inland, along rivers. Crocodiles may travel overland to find new territories.
Crocodiles are cold blooded (poikilothermic), like all reptiles, and must regulate their body temperature by moving to warmer or cooler locations throughout the day. They bask in the sun on riverbanks to warm up or float like logs submerged in water to cool down. During dry seasons, they retreat to their burrows in riverbanks to "estivate"--lounge about in a semi-dormant state.
What do American crocodiles look like?American crocs can grow to be 21 feet long. Like their relatives the lizards, their heads extend horizontally from long, four-legged bodies and end in a pointed snout. Their heavy, muscular tails are half their total body length. Their front feet have five toes, and their back feet have four, partially webbed.
Crocs are covered with heavy, olive brown or gray scales, which give them a rough, "pebbly" look. Their scales do not overlap, and the scales on their backs and heads are bony plates, called "scutes." Crocodiles shed their scales one by one, unlike snakes, which shed their entire skins.
Their eyes, ears, and nostrils are on the tops of their heads. When crocs are submerged in water, these are the only parts of them visible above the surface. Their eyes are large and silvery gray, with vertical pupils, like a cat's. Their nostrils are crescent shaped slits at the tips of their snouts. They have sixty-six to sixty-eight big, sharp, cone-shaped teeth. Because these teeth are attached to the outside of the jaw they are visible even when the crocodile's mouth is closed.
Croc teeth break off easily, and crocodiles grow new ones throughout their lives. A single crocodile may grow 3,000 teeth!
Crocodiles' rough, earth-colored scales and low profiles camouflage them, making them almost impossible to see in water or on muddy banks. Crocs rely on this near invisibility when they are hunting their prey.
Are crocodiles good swimmers?They are GREAT swimmers--fast and strong. They swish their long tails side to side to propel themselves forward. At low speeds or in shallows, they also use their legs. When they swim fast, they fold their legs close to their bodies to become streamlined. Juvenile crocodiles jump out of the water to snatch small birds from the air or off overhanging branches. Mature adults are too heavy to jump and must slither out of the water.
How do crocs breathe when they're in the water?Crocs keep the tips of their snouts above water most of the time, so they have no trouble breathing air. When they are fully submerged, a special valve automatically seals their nostrils. They can easily stay underwater for up to twenty minutes without breathing because their bodies adjust, sending oxygen to essential organs and slowing down metabolism. In captivity, crocs have been observed to go for two hours without breathing, with no bad effect.
Crocs also have a bony plate that separates their nostrils and mouths. This unique adaptation allows them to breathe when their mouths are full of water. A valve at the back of their throat stops water from pouring into their lungs and stomachs. They can open their jaws underwater at any time to snap at fish or drag large prey to shore. To swallow a fish or other animal, a croc must raise its head into the air. Crocs eat by flicking their heads and tossing unchewed food into the backs of their large throats.
Can crocodiles see and hear underwater?Corcodiles have good binocular vision and probably see in color. Their hearing is excellent. Underwater, a nictitating membrane or third eyelid protects the eye and reduces their visual acuity, and their ears close. To make up for diminished underwater sight and hearing, crocs have special touch receptors in their skin. These extend over the back and tail and are especially dense around the jaw and head. Scientists think that crocodiles' touch receptors help them perceive fish moving through water.
Crocodiles communicate with growls, roars, hisses, and squeaks by forcing air through their larynx. Hatchlings cry for help, mating males and females purr, and dominant males claim territory with roars.
What are crocodiles like out of water?On land, crocs belly crawl, walk high, and gallop. Belly crawling is lizard-like, belly-on-the-ground slithering. Walking high, crocodiles stand up on all four feet with their abdomens off the ground, moving their legs like a dog or cow. Galloping is walking high at highest speed, used for fast charges and quick escapes into water. Crocodiles can gallop ten miles an hour in short bursts and use speed and surprise for hunting and defense.
How do crocodiles get born?Female American crocodiles lay clutches of forty eggs, once every year, in nests made of mounded grass, twigs, leaves, and mud. Eggs have hard shells and soft inner membranes. All of the eggs in a nest hatch at about the same time, sixty days after they are laid. When a mother croc hears the cries of the first hatchlings, she opens the nest, which stimulates all of the other little crocs to emerge.
Crocodiles are neither male nor female when they are conceived. Gender is determined by the temperature in their nests when the eggs reach a critical stage of development. Warm or cold nests produce females. Intermediate nests produce males.
When the time comes, baby crocs must break their egg shells quickly or they will suffocate. Each hatchling has an "egg tooth"--a horny growth at the tip of its snout--with which it cuts through the inner membrane and pokes a hole in its shell. When a mother notices that a baby is having a hard time hatching, she takes the egg into her mouth and gently squeezes it to break the shell.
Breaking the shell is called "pipping." After the hard work of hatching, babies usually rest and gather strength for several hours. Egg teeth disappear by the time the hatchlings are a few weeks old.
Parental protection of eggs and hatchlings is unusual for reptiles, but crocodiles have a high degree of involvement with their young. Mothers are known to share nests and nurture each others hatchlings.
What are hatchlings like?New hatchlings are bright tan with black markings and eight or nine inches long. They follow mothers like a line of ducklings as they learn to swim and hunt. Within a year, if they are lucky, they grow to two feet and learn to be self-sufficient.
Hatchlings are vulnerable to many different predators, and crocodile adults are extremely protective of them. Both males and females respond aggressively to hatchling distress calls. But even with careful nurturing, only one in ten hatchlings survives to become an adult.
What do American crocodiles eat?Crocodiles are entirely carnivorous. Their principal food is fish, followed by turtles and crustaceans (crabs and the like). Hatchlings eat insects, snails, and other small aquatic animals. Large crocodiles seize birds and large mammals from the shore. Non-aquatic prey is dragged underwater until it drowns. Crocodiles do not chew or grind food in their mouths. They swallow prey whole or dismember it into pieces they can manage.
Crocodiles dismember prey into bite-sized pieces by gripping carcasses with their powerful jaws and flinging them from side to side until body parts fly off.
American crocodiles are unusually efficient at utilizing food. They hunt about once a week, usually at night. They can go without eating for more than a year. This causes them to loose all their excess weight, but they have no trouble hunting and eating as soon as prey is available again.
Crocodiles' stomachs contain the highest volume of acidic gastric juices of any vertebrate, which allows them to digest even bones and shells. They also swallow rocks, which help to grind bones, shells, and hair. At any given time, an adult crocodile's stomach may contain ten to fifteen pounds of rocks. Rocks not only aid digestion; they also help crocs submerge quickly and float with a minimum of body showing above the water line.
What eats crocodiles?NOTHING eats adult crocodiles except for human beings! Their meat is reported to taste great--and it's fat-free. Herons, storks and other large birds, wild cats, foxes, and coatimundis (rainforest racoons) eat juvenile crocodiles.
What's the difference between a crocodile and an alligator?Not much! Alligators live in fresh water; crocodiles prefer brackish, coastal waters. Alligators have U-shaped snouts, and only their upper teeth show when their mouths are closed. Crocodiles have V-shaped snouts and interlocking upper and lower teeth. Otherwise, they are similar in appearance and behavior--and all crocodiles, alligators, caimans, and gharials are crocodilians.
How did crocodilians survive the dinosaur extinctions?Scientists don't know exactly why crocodilians didn't perish with the dinosaurs. Fossil records show that crocodiles have hardly changed in 200 million years--American crocs look and behave a lot like their earliest ancestors. This makes them amazing champions of survival and adaptation.
Living in water probably provided them with protection from asteroid impacts and global dust clouds. Scientists have learned that crocodiles aren't disrupted or upset living in prolonged darkness, and they can tolerate extremely dirty water.
Remarkably strong immune systems help crocodiles survive injury, including loss of whole legs. They will eat dead animals, and they can go a long time without food. They can slow their heart rate to two or three beats a minute to conserve energy, and they tolerate cool temperatures. They live relatively long lives for reptiles--as long as sixty years. And they nurture their young, teaching them survival skills and protecting them from predators.
Crocodile ancestors probably shared all of these characteristics, which gave them advantages that dinosaurs didn't have. For example, crocodiles may have been able to wait for years, until environmental conditions improved, before mating and producing new generations. Some dinosaurs may not have survived long enough to produce young in more tolerable conditions.
Do crocodiles help humans?Crocs are prized for their beautiful hides and tasty meat. Over-hunting depleted croc populations in the twentieth century, but crocodile ranches and controlled hunting are helping the croc hide industry make a comeback.
Crocodiles have been important to many peoples' mythologies and ritual practices. The ancient Egyptians and the Central American Olmecs worshiped crocodile gods.
Contrary to legend and folklore, crocodiles do not prey on human beings. One exception to this rule is the Nile crocodile, which may have developed a taste for human flesh long ago, when Egyptian priests fed them human sacrifices.
Crocodiles are also an indicator species. When environmental poisons are introduced into marine habitats, crocodiles are among the first animals to show negative effects. This makes them interesting to environmental scientists and conservationists. For example, pesticides containing estrogens disrupted alligator reproduction in Lake Apopka, Florida. This harm was caused by exposure to tiny doses of 100 parts per trillion--far below allowed levels in human drinking water.
Species and Range.American crocodiles are common in tropical wetlands from the southern United States to northern South America. They are reptiles of the Crocylia order, Crocodylidae family, crocodylus genus--species Crocodylus acutus.
Are crocodiles endangered?In the twentieth century, hunting dramatically reduced crocodile populations. No species went extinct, and now that hunting is controlled in the United States and other countries, populations are rebounding.
Many people are frightened by American crocodiles, which have attacked children and even killed adults on a few occasions when their habitats have been invaded. Other people fear that crocodiles will eat their pets or livestock. For this reason, conservationists and animal protection groups offer educational programs to help the public learn about the amazing crocodilians.
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