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Crocodilians in the US: The American Alligator and The American Crocodile
Crocodilians are the largest reptiles on the planet and have remained evolutionarily unchanged for millions of years. All crocodilians are evolutionarily built to live both on land and in the water. They are cold blooded, lay eggs, and lack gills unlike amphibians and fish. Although there are twenty-three species of crocodilians (Order Crocodylia) in the world, there are only two that are native to the United States, the American Alligator, and the American Crocodile. While the American Alligator can be found only in the United States, the Crocodile is much more readily found in central and South America and the Caribbean. Although they are two very different species, they are often confused because of similarities in appearance, range and behavior. It is true that they do have numerous things in common, yet there are several key characteristics that make them distinctly different. Both species also have a history of conservation issues but are quite different in this respect today. Finally, both species can be found in Southern Florida, particularly in the Everglades national park, where they are currently encountering other problems relating to their survival.
The American Alligator, one of only two alligators in the world, can only be found in the Southeastern United States. Although it has populations in ten different states including Mississippi, Texas, Arkansas, Alabama, Georgia, North and South Carolina, and Oklahoma, they are abundant in Florida and Louisiana. Both states have populations into the millions. This range is unique for a crocodilian, as it is the farthest north of all of the species. In fact, one of the key differences between the Crocodile and the Alligator is the Alligators ability to withstand temperatures up to forty-five degrees Fahrenheit.
The American Crocodile, on the other hand, is quite rare in the United States with only around 1200 individuals residing on the southern tip of Florida. The crocodile prefers slightly warmer areas and is therefore found in western and southern Mexico, Central America, and the northern tip of South America. They are even found commonly in the Caribbean, as they are known to swim far out to sea. Crocodiles have the ability to expel salt through a gland inside of their mouth, allowing them to live in brackish and salt water, unlike the alligator (Cheatham 2001).
The primary habitat of the American Alligator is wetland areas, usually with a lot of tree cover. These areas include places such as swamps, bayous, lakes, marshes and other bodies of water. Generally the males of the species will reside in more open areas such as rivers and lakes, while the females stay closer to the middle of marshes and swamps where they are able to nest. Alligators are primarily a freshwater dwelling species, yet they can still tolerate salty or brackish water. The American Crocodile lives in a very similar habitat, only of the salt or brackish water variety. Both species are the regulators of their wetland habitats, being the largest predators in the food chain (Kushlan 1974).
The American Alligator and the American Crocodile are very similar in appearance. They both have long, muscular bodies, covered with armored, scaly skin. Their legs are longer in proportion to other lizards, which allows them to walk without dragging their bodies on the ground (Weidensaul 1991). Their tails are extremely strong, used for swimming, and are roughly half their body length. Finally, they both have long jaws filled with conical, replaceable teeth and eyes and nostrils on the tops of their heads, that allow them to submerge their bodies underwater.
When examined more closely however, the American Alligator and Crocodile are actually easily distinguishable. The alligator is the smaller of the two species, with an average size of 6 to 16 ¸ feet long. The crocodile, however, is generally 7 ¸ to 12 feet in Florida, though it grows closer to 20 feet in South America. The alligator is generally much darker in color, closer to black, while the crocodile is a lighter grayish tan (Conant 1998). The most obvious physical differences between the two are found in the anatomy of their heads. The alligator has a rounded U shaped snout while the crocodileÕs snout is a more pointed V shape. Finally, the fourth tooth on the crocodiles lower jaw prominently sticks out when itsÕ mouth is closed while this is absent in the alligator. Although they may look alike at first, the American Alligator and American Crocodile are actually quite physically different.
Although different in appearance, the American Alligator and the American Crocodile are extremely similar in one aspect, feeding. Both species will eat just about anything including fish, mammals, birds, amphibians, other reptiles, crustaceans and insects. The larger the individual, the larger prey they will consume, with some of the larger crocodiles eating large mammals. Both species are also known to be cannibalistic, with larger individuals preying on smaller ones. Because their jaws do not allow them to chew, crocodiles and alligators rip and tear their food apart. They also will roll prey in circles underwater, an action called the Òdeath roll.Ó Crocodiles and alligators are even known to stash their prey in underwater nooks to save for later (Lockwood 2002). Finally, to swallow their food, they lift their heads up to allow the food to slide down their throats. Despite popular opinion, neither species feeds on humans, though there are a small few attacks, normally because of invasion of territory. These feeding rituals have adapted in both the American Alligator and the American Crocodile.
Reproduction strategies also serve to separate the two species. The mating season for the both begins in early April when they reach about 6 feet in length. For males, this will take around 7 years while females grow slower and will reach sexual maturity in 9 or 10 years (Davis et al 2001). In both species, the male will become aggressive during mating and try to attract a mate. In alligators, the male will lower his body into the water and bellow, making droplets of water ÒdanceÓ on his back. In both species, the female will build the nest and care for the young. The nests of the two species are quite different however. The Crocodile digs a hole into the sand while the alligator creates a larger mound of vegetation to lay her eggs in. The mother alligator will also keep a much closer watch on her nest while the eggs incubate while the croc will generally leave and return when the eggs are ready to hatch (Lockwood, 2002). In both species however, the temperature of the eggs determines the sex of the hatchling. Warmer temperatures, 90-95, produce males, middle temps, around 87-90 produce both sexes, and colder temps, 82-87, produce females. Both mothers help their eggs hatch and protectively care for them, parental behavior that is unique for a reptile (Ogden 1978).
Finally, though some things are similar, there are some differences in general behavior that differentiates the two species. Both species live in water and on land and use this to control their body temperature. They both spend much of their time basking in the sun. They are also both much more active at night, as the temperature is more comfortable then. Generally, however, crocodiles are more aggressive than alligators are (Garrick 1977). Interestingly enough, although the croc is more aggressive, alligators are much more vocal than the crocodile. A male alligator bellow is far louder than the vocalizations of the larger crocodile (Conant 1998).
Both the American Alligator and the American Crocodile have had extremely low populations in the past due to over hunting. For the alligator, the United States placed it on the endangered species list in 1973. The Crocodile ended up benefiting from this, as the species were hard to distinguish from one another. Currently, American Alligator numbers have risen so high that they are no longer on the endangered species list (Weidensaul 1991). There are even hunting seasons and nuisance programs that regularly hunt the animals in the wild now. The American Crocodile is in a much different situation than the alligator however. Although the US has taken it off of the endangered species list, it is still endangered in the other countries where it is more abundant. Although many of these countries have protection programs in place, poaching is still a common occurrence due to lack of regulation (Cheatham 2001).
The Everglades national park in Florida is home to both the American Alligator and the American Crocodile. Although numbers of crocodiles are too small to really see the issues, American Alligators are encountering problems within the park. It has been found that alligators in the park are measurably smaller than others in the wild. This is caused by a lack of proper food and habitat (Kushlan 1990). Also, since 2003, the alligators place in the top of the food chain is being challenged by an invasive species, the Burmese Python. These pythons not only compete for food and space, but have even been known to eat alligators, threatening their livelihood in the park. Although the have overcome past threats, the Everglades alligators are still encountering problems today.
The American Alligator and the American Crocodile are the only two species of crocodilians that are native to the United States. The alligator can only be found within the states, while the crocodile is much more common in countries to the south. Both species are commonly confused because of similarities in appearance, behavior and habitat, yet they have numerous differences. They have also faced near extinction in the past and are still threatened in some areas, yet protection programs for both species are still in place to make sure these two species continue to thrive as they have for millions of years.
Literature Cited
Cheatham, Karyn Follis. The Crocodile. San Diego: Lucent Books, 2001.
Roger, Conant,. Field guide to reptiles & amphibians eastern and central North America. Boston: Houghton Mifflin, 1998. 38-40.
Davis, L. M., Glenn, T.C., Elsey, R. M., Dessaures, H. C., and Sawyer, R. H. (2001). Multiple paternity and mating patterns in the American alligator, Alligator mississippiensis. Molecular Ecology, 10, 1011-1024.
Garrick L. D. and Lang J. W., (1977). Social signals and behaviors of adult alligators and crocodiles. American Zoologist, 17(1), 225-239.
Kushlan. J. A. (1974). Observations on the role of the American Alligator (Alligator mississippiensis) in the Southern Florida wetlands. Copeia, 1974(4), 993-996.
Kushlan, J. A. and Jacobsen, T. (1990). Environmental Variability and the reproductive success of Everglades alligators. Journal of Herpetology, 24(2), 176-184.
Kushlan, J. A. and Mazzotti, F. J. (1989). Historic and present distributions of the American crocodile in Florida. Journal of Herpetology, 23(1), 1-7.
Lockwood, C.C. The Alligator Book. C.C. Lockwood. 2002.
Lutz, P. A. and Dunbar-Cooper, A. (1984). The Nest environment of the American crocodile (Crocodylus acutus). Copeia, 1984(1), 153-161.
Ogden, J. C. Status and Nesting Biology of the American Crocodile, Crocodylus acutus, (Reptilia, Crocodilidae) in Florida. (1978). Journal of Herpetology, 12(2), 183-196.
Weidensaul, Scott. Crocodiles and Alligators. New York: The Image Bank, 1991.
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