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 sitea 900-acre area adjacent to the San Diego Wild Animal Parkto 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 youthey are so well camouflaged that they can be right next to you and without the transmitter you would completely miss them."
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 roadsand 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 lionsall of which, like the snakes, can broadcast to researchers what they need.
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