CROCODILES AND FALSE GHARIALS: Crocodylidae

PHYSICAL CHARACTERISTICS

Fourteen species of crocodiles make up this family, including one called a false gharial. (An Indian gharial also exists, but it is not a crocodile and is instead listed in its own separate family.) The crocodiles are medium to large reptiles, with adults ranging from about 5 feet (1.5 meters) long in the smallest species to 20 feet (6.1 meters) long in the largest. Within species, females are smaller overall. For example, female Johnstone's crocodiles typically grow to 5 feet (1.5 meters), while the average male is about 6.5 feet (2 meters) long. In all species, the tail is about as long as the rest of the body.

Crocodiles, alligators, and caimans are often confused because they all have armor-like scales on the back and tail, a powerful tail, a pair of back legs that are stronger and larger than the front pair, and toes that are webbed on the back pair of feet and unwebbed on the front pair. Perhaps most noticeably, they also all share a long snout filled with teeth. Crocodiles, however, have something the others lack. Counting from the front of the mouth, the large fourth tooth on each side of a crocodile's lower jaw shows outside of the mouth when the jaw is closed. In other species, this large tooth is hidden, although many other teeth on the upper jaw may be visible when the mouth is clamped shut.

GEOGRAPHIC RANGE

At least one species of crocodiles lives in each of these continents: Africa, Asia, Australia, North America, and South America.

HABITAT

Crocodiles spend their time in or near the water. Unlike alligators and caimans that only live in freshwater habitats, crocodiles can survive in freshwater or saltwater. Crocodiles do not, however, swim around in the open ocean. Instead, they live in saltwater marshes or creeks. They have special organs, called salt glands, that get rid of this extra salt so they can survive. Without these organs, they could not live in saltwater. Crocodiles make their homes in warm, tropical areas, although the mugger crocodile and the American crocodile can survive in subtropical regions that are slightly less warm. Those that live in areas with periods of extremely dry weather sometimes find that their watering holes disappear, and they must spend the next few weeks buried deep underground until the rains return.

DIET

Crocodiles are meat-eaters that shift from eating insects and spiders as youngsters to larger and larger animals as they grow. Adults of the largest crocodiles, like the Nile crocodile, eat animals as big as warthogs, cows, and sometimes humans. They are skilled hunters that sneak up on prey by ever so slowly swimming closer and closer, and then lunging out with mouth open to clamp down on the surprised animal. This method of sneaking up on prey is called stalking. Once the jaw snaps shut, the prey has little chance of escaping. With a captured mammal, the crocodile typically pulls it underwater, and when the animal drowns, tears off chunks to swallow. Crocodiles also hunt for prey by ambush, which means that they stay still in the water and wait for a prey animal to happen by. Besides live meals, crocodiles will also eat the dead animals they find.

BEHAVIOR AND REPRODUCTION

Crocodiles are most active at night, which is when they usually look for food. In the morning and evening, they frequently crawl out of the water and lay quietly in an open area to sunbathe, or bask. This helps warm their bodies. Crocodiles are excellent swimmers. By slowly swishing the strong tail from side to side, they can push their bodies through the water without having to paddle with their legs. They can also move well on land. Usually, they walk slowly, dragging the tail behind them, but when they are in a hurry, they run quite quickly while swinging the tail back and forth in the same motion they use when swimming.

Crocodiles usually get along fairly well with one another, but during the mating season, males can become bad-tempered. Usually, a large male need only sound a loud bellow or slap his head against the surface of the water to scare off a smaller male, but sometimes they fight by biting one another. The bites are hard enough to cause wounds that leave noticeable scars. Besides their bellows, crocodiles make other sounds, such as growls and hisses, when they feel threatened.

Male crocodiles may fight each other over the females during mating season, and one male may have babies with several females in a single year. All female crocodiles lay eggs rather than giving birth to babies. The females in some species use their back legs to dig a hole on land, and they bury their eggs there. These females lay their eggs in the dry season, and the eggs hatch when the rains come. In other species, the females lay their eggs in a pile of rotting leaves and dirt that they scrape together. The females lay their eggs at the beginning of the rainy season, and the eggs hatch during the wettest time of year. Depending on the species, females may lay 40 to 70 eggs at a time, with hatching occurring two to three months later. If the nest is especially warm, the eggs all hatch into males. If the nest is particularly cool, the eggs all hatch into females. A mother crocodile stays close to her nest until the eggs are ready to hatch. The baby crocodiles begin to make soft quacking noises when they are ready to break out of their eggs, and the mother rushes to the nest to pick up and carry each of her babies to the water. The mother, and sometimes the father, watches over the young for several weeks, but despite this care, fewer than one out of 10 babies escapes the many predators in their habitat. Those that do survive to adulthood can look forward to a long life. Crocodiles often live for 70 to 80 years in the wild.

ONE TON BEAST

The saltwater crocodile is a huge animal. The largest species of all crocodiles and alligators, it can grow to more than 20 feet (6.1 meters) long and weigh 2,200 pounds (1 metric ton). Occasionally, humans tangle with these beasts and lose. One of the most often-told tales of human versus crocodile dates back to World War II, when hundreds of Japanese soldiers hid in a swamp near Myanmar. A large group of saltwater crocodiles set upon the men that night, killing all but 20 by morning.

CROCODILES, FALSE GHARIALS, AND PEOPLE

People have long been fascinated by crocodiles, which are often mentioned in legends. Some people hunt these animals for their meat or skin, and some collect and eat their eggs. Crocodiles are perhaps most known, however, as killers of humans. Although death by crocodile is very rare, it does happen occasionally, especially when humans who visit their habitat are careless.

CONSERVATION STATUS

According to the World Conservation Union (IUCN), nine of the 14 species are at risk. This includes three listed as Critically Endangered, which means they face an extremely high risk of extinction in the wild; two as Endangered and facing a very high risk of extinction in the wild; three species as Vulnerable and under a high risk of extinction in the wild; and one as Conservation Dependent, which means it could be at risk if conservation efforts ceased. In addition, the IUCN describes one species as Data Deficient, which means that scientists have too little information to make a judgment about its threat of extinction. The U.S. Fish and Wildlife Service lists 12 of the 14 species as Threatened, or likely to become endangered in the foreseeable future, or Endangered, which means they are in danger of extinction throughout all or a significant portion of their range. Most of the species are at risk because of habitat loss and overhunting. Several efforts are now under way to help protect these animals.

AMERICAN CROCODILE (Crocodylus acutus): SPECIES ACCOUNTS

Physical characteristics: The American crocodile is large, with the males averaging 10 to 11 feet (3 to 3.5 meters) long and females usually 8 to 10 feet (2.5 to 3 meters) in length. The largest males, however, can reach a full 20 feet (6 meters), but such giants are extremely rare. Its body is a bit thinner than most crocodiles, and its snout becomes narrower toward the tip. It also has a noticeable lump on its snout in front of its eyes. Adults are usually dark brown to light brownish gray with a white belly. Youngsters are yellow to greenish gray with dark markings.

Geographic range: American crocodiles live in large groups in southern Florida, southern Mexico, Central America, numerous Caribbean islands, and northern South America.

Habitat: Also known as the American saltwater crocodile, this species can survive in various habitats from freshwater canals to somewhat salty marshes near the ocean coast.

Diet: Young American crocodiles catch and eat insects, tadpoles and frogs, crabs, and fish, and then switch to larger prey as they grow. Adults are able to feed on animals as large as cows and, in very rare cases, humans.

Behavior and reproduction: American crocodiles usually hunt at night and spend most of their days resting in the water or basking or sunbathing on shore, especially in the mornings and evenings. During very dry periods, they will dig a tunnel and remain inside until the rains return. Males and females mate from March to May, and each female lays 30 to 60 eggs in a hole that she digs. Sometimes, the mother may lay her eggs in a pile of rotting leaves and dirt instead. She stays nearby until the eggs hatch 80 to 90 days later. She then helps her babies out of the nest and watches over them for a few more days.

American crocodiles and people: This species very rarely attacks humans. Some humans, however, raid the crocodiles' nests to collect their eggs for food.

Conservation status: The World Conservation Union (IUCN) considers this species to be Vulnerable, or facing a high risk of extinction in the wild. The U.S. Fish and Wildlife Service designates it as Endangered, or in danger of extinction throughout all or a significant portion of its range. The primary threat to this animal comes from habitat loss. ∎

NILE CROCODILE (Crocodylus niloticus): SPECIES ACCOUNTS

Physical characteristics: A large and bulky-bodied species, the Nile crocodile has a very lumpy, dark brown to gray back and a light yellow, white, or gray belly. Youngsters are greenish brown to brown with dark markings. Females usually reach about 8 feet (2.5 meters) long, and males typically grow to about 11.5 feet (3.5 meters).

Geographic range: Nile crocodiles live in Africa south of the Sahara Desert and on Madasgascar off Africa's southeast coast.

Habitat: Nile crocodiles mainly live in freshwater habitats, including marshes, lakes, and rivers.

Diet: The adult diet is mostly fish, although Nile crocodiles will also eat large mammals, such as warthogs and antelopes.

Behavior and reproduction: Nile crocodiles spend much of their time in the water, either stalking prey or lying in wait for an animal to come close enough to attack. With their powerful jaws, they can clamp onto even large animals and drag them underwater. After the animal drowns, the crocodile may twirl the animal in the water in an attempt to tear off a chunk of flesh to eat. Nile crocodiles often live in large groups and often bask together on the shoreline. During the August-to-January mating season, however, males will fight one another. After a male and female mate, the female goes off to dig a hole high on shore and lay her 50 to 80 eggs inside. The mother remains nearby, and 80 to 90 days later, she helps her now-hatched young out of the nest and to the water. The young stay under their mother's watchful eye for another month or so, and then go off on their own.

Nile crocodiles and people: These animals occasionally attack and kill ranchers' cattle and other livestock, and very rarely, a person. Some people hunt this reptile for its meat and skin.

Conservation status: Although it was once overhunted, the World Conservation Union (IUCN) no longer considers this species to be at risk. The U.S. Fish and Wildlife Service, however, lists it as Threatened, or likely to become endangered in the foreseeable future. Numerous guidelines are in place to help make sure the crocodile survives into the future. ∎

FOR MORE INFORMATION

Books:

Cleaver, Andrew. Snakes and Reptiles: A Portrait of the Animal World. Wigston, Leicester: Magna Books, 1994.

Daniel, J. C. The Book of Indian Reptiles and Amphibians. New Delhi, India: Oxford University Press, 2002.

Irwin, Steve, and Terri Irwin. The Crocodile Hunter. New York: Penguin Putnam, 1997.

Lamar, William. The World's Most Spectacular Reptiles and Amphibians. Tampa, FL: World Publications, 1997.

Ross, C. A., ed. Crocodiles and Alligators. New York: Facts on File, Inc., 1989.

Rue, Leonard Lee. Alligators and Crocodiles. Wigston, Leicester: Magna Books, 1994.

Schmidt, K. P. A Check List of North American Amphibians and Reptiles. Chicago: University of Chicago Press, 1953.

Smith, H. M., and E. H. Taylor. An Annotated Checklist and Key to the Reptiles of Mexico Exclusive of Snakes. Washington, DC: Bulletin of the U.S. National Museum, 1950.

Webb, G. J. W., and S. C. Manolis. Crocodiles of Australia. New South Wales, Australia: Reed Books Pty, Ltd., 1989.

Web sites:

"Crocodilian Species List." Florida Museum of Natural History. http://www.flmnh.ufl.edu/cnhc/csl.html (accessed on December 15, 2004).

"Crocodylus niloticus (LAURENTI, 1768)." Florida Museum of Natural History. http://www.flmnh.ufl.edu/cnhc/csp_cnil.htm (accessed on December 15, 2004).

"The Reptiles: Alligators and Crocodiles." Nature. http://www.pbs.org/wnet/nature/reptiles/ (accessed on December 15, 2004).