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Zoo-ology

May 15, 2011 at 12:15 a.m.

Two American alligators lie in the mud.

BY JUDIE FARNSWORTH

Just say "alligator" or "reptile" and there's an immediate response ranging from fascination to a notable cringe. American alligators are part of the family of reptiles called Crocodilians, along with crocodiles, caimans and gavials.

It is notable that while most reptiles typically offer no parental care, alligators and other crocodilians are pretty good moms, all things considered. And - it may all begin with a dance.

In order to attract a female or drive off other alligators, a male may roar - even though alligators have no vocal chords. He pulls air into his lungs. His head is raised and his tail slowly waves above the water. His throat puffs out and starts to vibrate as air is pushed out.

A low-frequency signal is projected through the water, vibrating the ground and nearby objects. The water over his back begins trembling and a deep-toned roar is heard. This is referred to as a "water dance," or in the case of a group of courting alligators - "alligator dances." Imagine a swamp booming with roaring alligators. Thrilling for a debutante alligator I expect, but thunder or sonic booms may also cause a male to roar (sorry ladies).

After the dance and choosing a prince charming, the female soon begins to build a huge nest, often measuring seven feet in diameter and two to three feet high. It's constructed of mud and vegetation that decomposes to provide heat; like a compost pile. She digs out an area and produces 20 to 50 goose-egg-sized eggs, which she covers.

The temperature of the nest determines the sex of the babies (during the first three weeks). Higher temperatures, 91 degrees or more, produce males. Lower temperatures, 85 degrees or less, produce females.

The female doesn't stay on the nest, but guards it from other alligators, including her prince, and predators like raccoons. Repairs are made when necessary. Sometimes turtles dig and lay their eggs in the nest. It's dangerous, to be sure, but if successful, the alligator will be guarding the turtle eggs, too.

The eggs incubate for around two months. Alligators have great hearing and the female will hear chirping noises from inside the buried eggs. She uncovers the eggs and may help open them. She may also form a pouch shape with her tongue, and carry the young to water, where she gently shakes her head back and forth, letting them swim out. The young are between six to eight inches with handsome yellow bands. A female will defend her young, particularly during the first year.

Newly hatched alligators live in groups called pods that may be from several nests. Although very territorial as adults, juveniles are tolerant of others near the same size. They grow about a foot a year. Many will fall victim to predators in the first couple of years. At four feet, their chances of survival are good. Alligators are considered mature at 6 years. Their average lifespan is 50 years.

We recently received some new young alligators estimated to be between 1 and 4 years old. Their exhibit is almost ready for them. Come watch them grow.

Judie Farnsworth is a longtime volunteer at the Texas Zoo, specializing in educational programs.

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