Saturday, May 26, 2007

Desert island amphibian

It's a question that's asked at least once a day everywhere in America: If you were stranded on a desert island and could have only one species of amphibian sharing the island, which would you choose? I have two: Gulf Coast toad and green treefrog. They both inhabited my community garden in New Orleans (where both pictures were taken), they always called their dulcet tones when I was camping down south, and the toad is a voracious eater of the slug, a garden nemesis. Southeast Missouri doesn't harbor populations of Gulf Coast toads, but green treefrogs are common amphibians around the few remaining swamps in the area. Swamp drainage and habitat destruction has likely impacted their populations, but no amphibian surveys were conducted before the drainage projects began, so no one really knows for sure.

Southeast Missouri represents the northwestern limit of the green treefrog's range. They are the most common treefrog in the southeast U.S. and their delightful choruses can be heard from the western side of Crowley's Ridge to southern Illinois, then south throughout the embayment. Unlike last spring, the park's swamp is full of water this year. Green treefrogs, who depend on permanent water with emergent and floating vegetation for breeding, began chorusing in April, a whole month earlier than last year. Standing on the front porch at night, you can hear their earnest "quank quank" from two miles away. Green treefrogs generally call from late May through July with egglaying taking place in June or July. Females lay between 500 and 1,000 eggs which they attach to emergent or floating vegetation like sturdy sedges and cattails.

In the late 1970s, a catfish farmer from the Ozarks introduced a population of green treefrogs to his heated pond in Camden Co. A small population persists, but seems to be confined to the heated pond. Amphibian enthusiasts in Camden Co. regularly mistake the green phase of the common gray treefrog for the green treefrog. Unlike the gray treefrog, green treefrogs have yellow spots on the back and a white or yellow stripe that extends from the lip down the side; the stripe isn't present in all animals and populations in different locations have diverse stripes. A study in southern Mississippi several years ago tracked populations based on the stripe: animals in southern Alabama had clean white stripes, while certain animals in Louisiana had yellow stripes. At Fort Pickens National Park in Florida, the population lacked the stripe altogether.

Last week, when I asked a table of colleagues what their desert island amphibian would be, some answered bullfrogs because they provide a food source. Others said Ozark hellbenders because the animals only live in fast, clean Ozark streams, so the presence of the Ozark hellbender would mean the desert island would have an Ozark stream. I stuck with green treefrogs for impractical reasons. I like the sound of their chorus, they hang out under porchlights at night, and, frankly, they're cute. Next question: desert island reptile. I choose three toed box turtle and American alligator, and I wouldn't eat either of them.

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