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Radio Transmitter-
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Bijal P. Trivedi for National Geographic Today |
| October 31, 2002 |
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A red diamond rattlesnake lies motionless on the operating table at the San Diego Zoo hospital. With a quick slit of the skin, a veterinarian opens up the snake and inserts a radio transmitter the size of a double-A battery, then sews up the incision. A week or so later, the snake slithers back into the wild—broadcasting a signal to researchers about where and how it lives. In southern California real estate, as elsewhere, location is everything and both man and beast are competing for coveted locales. "The San Diego area has more threatened and endangered species of plants and animals than any other county in the contiguous United States," says Tracey Brown, a reptile ecologist at California State University at San Marcos. In fact, California's so-called Floristic Province—125,000 square miles (325,000 square kilometers) of the western coast from northern Baja to southwestern Oregon—is one of the world's most biologically diverse environments. But only about 25 percent of the original habitat remains. Now the challenge is to balance development and conservation. "We want to protect land that works for the animals," says Robert Fisher, a zoologist at the U.S. Geological Survey Western Ecological Research Center in San Diego. Fisher and his colleagues are part of a broader effort to identify and conserve land essential to the animals' survival. "We let the snakes tell us what they need," Brown says. Stalking Snakes The snake-tracking research began in 1995 after Fisher and Ted Case, a biologist at University of California at San Diego, noticed that locally some snake species were declining and, in some cases, dying out. Fisher and Case launched a project to survey the snakes. In 1999, the researchers began implanting radio transmitters in the snakes. In 2001, Brown, funded by the San Diego Zoo and the Favrot Fund, joined their efforts. The researchers studied three snakes: the red racer, a fast-moving species that can travel up to several miles per day and whose home range can extend hundreds of acres; the rosy boa, a docile snake common in the pet trade, and the red diamond rattlesnake. The boa and the rattlesnake are homebodies that seldom travel more than a couple of miles in a lifetime. Today up to 20 snakes are roaming with transmitters that send signals picked up as beeps by a handheld antenna-equipped receiver. Every other day researchers enter their study site—a 900-acre area adjacent to the San Diego Wild Animal Park—to locate their high-tech snakes. The area's coastal sage scrub is prime snake habitat that contains 16 of the 17 species normally found in the San Diego region. "We wave the antenna around and then listen," says Brown. "The beeps become louder as you get closer to the animal. They can certainly surprise you—they are so well camouflaged that they can be right next to you and without the transmitter you would completely miss them." Snake Secrets Researchers use a GPS unit to determine the snake's precise location. Over several years the data track each animal's wanderings and preferences. Tracking has revealed, for example, that rattlesnakes prefer communal dens during the winter. Between November and March, Brown has found up to seven males and females curled up together in a den. During this "over-wintering period," the rattlesnakes don't hunt and rarely emerge from their den. But rosy boas, which winter in rodent burrows, are known to poke their head out on an unusually warm day. The trackers have also learned that snakes create a mental map of their environment that allows an individual to return to the same bush or rock year after year. The research has also revealed that rosy boas don't like to cross dirt roads. Red racers, by contrast, cross open areas all the time. The findings can help planners design reserves that align with the snakes' natural habitats. For example, reserves could better serve the racers if a short wall lined the roads—and redirected the snakes back into the park. Fisher has received funding from the USGS, the U.S. Fish and Wildlife Service, the National Oceanic and Atmospheric Administration, California Fish and Game, the Nature Conservancy, and others. Fisher plans to use the radio transmitters and GPS collars to complete similar surveys of roadrunners, bobcats and mountain lions—all of which, like the snakes, can broadcast to researchers what they need. Join the National Geographic Society Join the world's largest nonprofit scientific and educational organization, and help further our mission to increase and diffuse knowledge of the world and all that is in it. Membership dues are used to fund exploration and educational projects and members also receive 12 annual issues of the Society's official journal, National Geographic. Click here for details of our latest subscription offer: Go>> |
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