by Janet Grischy

Created on: September 28, 2008

There have been alligators on earth for 200 million years. They look prehistoric, too, huge, dark, and armored, lazing on a sunny mud bank until they suddenly lunge at their hapless prey. An alligator can weigh 800 pounds or more, and be on average thirteen feet long. One on Marsh Island in Louisiana was measured at nineteen feet, and weighed over a thousand pounds. They can live more than fifty years in the wild, while captive alligators have been documented at ages greater than seventy.

There are only two species of alligator, the American alligator, alligator mississippiensis, and the somewhat smaller Chinese alligator, alligator sinensis. The American alligator's range is expanding, while the Chinese alligator is extremely endangered, with the wild population possibly reduced to about two dozen individuals in the Yangtze River valley.

The breeding female American alligator builds a huge nest of vegetable matter and silt about five to seven feet across and one to three feet high. (The nest of the Chinese alligator is similar, but smaller.) She fills it with up to 88 eggs, although a more common number is fifty. Then she covers them with more mud and foliage. The vegetation rots and warms the nest in the same way that a compost heap heats up from the heat of decomposition. Alligators, like all reptiles, are cold-blooded, ectothermic, so the alligator can't warm the nest with her body heat the way a bird or mammal would.

The gender of an alligator is determined by temperature, not genetics. As the nest heats, different parts of it reach different temperatures. The eggs in the warmer parts of the nest become males, while the eggs in the cooler parts become females. If the whole nest is above 93 degrees Fahrenheit, all the hatchlings will be male. Below 86 degrees F., all will be female. Nests on levees tend to be warmer, and produce more males, while nests in the cooler marsh tend to produce more females. In nature, nests tend to produce about five females for every male.

When the eggs hatch, the mother will help the hatchlings make their way to water. She will protect her offspring somewhat for their first year, if they stay in her territory, and they will need protection. Adult male alligators eat alligator young. It is estimated that 50% of hatchlings do not live past their first year.

Once they are grown though, alligators are the apex predator in their range. Their main enemy is humankind, who destroys their habitat and sometimes outright kills them for their

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