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CA Press: Researchers track snakes to map out their habitats

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Posted by W von Papinešu on April 22, 2003 at 13:07:10:

UNION-TRIBUNE (San Diego, California) 22 April 03 Researchers track snakes to map out their habitats (James Steinberg)
San Pasqual: Most people will go to any length to avoid a rattlesnake. Jeff Lemm and Tracey Browne go out of their way to find them.
Twice a week, they hit the trail to track 14 radio-tagged red diamond rattlers on 900 rugged acres at the San Diego Wild Animal Park.
Lemm and Browne are researchers with the Zoological Society of San Diego's Center for the Reproduction of Endangered Species.
The snakes, nicknamed "rubers," from their scientific designation, Crotalus ruber, are found in coastal sage scrub from the Grapevine north of Los Angeles into Baja California. Locally, however, 90 percent of the coastal sage scrub habitat has been lost to development, Lemm said.
"There's a great concern about their future because habitat is hard to come by. San Diego County has lost the most habitat and has more endangered species than any other county in the United States," he said.
The red diamond is a species of "special concern," Lemm said. "There isn't enough data to know if the species is endangered or threatened. That's why field studies are so important."
For the past two years, Lemm and Browne have followed 14 of the estimated 500 or so red rattlers thought to inhabit the Wild Animal Park. The snakes have small radio transmitters, about the size of an AA battery, that were implanted under anesthesia at the San Diego Zoo veterinary hospital, Browne said.
Red diamonds are the least aggressive of the four rattler species in San Diego County, Lemm said. (The others are the Southern Pacific, the speckled and the sidewinder, partial to the deserts east of the coastal mountains.)
Their lack of aggression also makes them the most dangerous, said Allison Alberts, head of the Zoological Society's division of applied conservation. "They don't rattle, and people step on them."
The snakes are well camouflaged, and they blend Ė almost to the point of invisibility Ė with their environment, which consists primarily of sage, chaparral and cactus.
Humans mostly encounter the rubers when they crawl into yards or garages, Lemm said. While moving the snakes somewhere else is preferable to killing them, relocating them too far away from where they are caught could harm them.
The rubers occupy a home range of only about five to 10 acres, Browne said.
Too much of a move and the snake could be at a disadvantage when it comes to finding water and food, Alberts said. Rubers eat small mammals, mostly mice and ground squirrels.
"At the Wild Animal Park, the only ones we translocate are the ones that show up in the exhibit areas," Alberts said.
In the field, Lemm and Browne have a fairly good idea where to start their search for each snake. Since the implanted radio transmitters have individual frequencies, tracking the snakes to within a few yards isn't that difficult.
But then it becomes a rock-by-rock, bush-by-bush search. Once they find a snake, Lemm measures its external temperature with a laser device, and Browne determines its location by GPS. The rate at which the radio signal beeps is used to determine internal temperature. All data are entered on a hand-held computer.
Plotted on a map, the GPS readings can be turned, over time, into a plot of each snake's home range. No. 20, a female, for example, has halved her territory from 2001 to 2002, while No. 24, a male usually associated with her, has extended his range during the same period, Lemm said.
Lemm and Browne began a recent search in the field before 9 a.m. and located most of their charges by early afternoon. No. 34, a female, was halfway up a hillside, and No. 29, Allison's Den Snake (the only one with a name), was just a few yards from the rock outcrop she favors.
"It may be in the den," said Lemm, peering into the opening in the rocks. Then he looked down. "It's under my feet!"
He picked up the docile reptile with a snake hook made from the shaft of a golf club.
"She's reading cold . . . only 13 degrees Celsius," Browne said.
No. 29 has the smallest range of any snake in the group and rarely ventures more than 50 to 100 yards from the den, first identified by Alberts, hence the reptile's name.
While the team currently tracks 14 snakes, other snakes have been monitored in the past.
The day's only disappointment was No. 27, found easily enough, but dead less than 24 hours. Dropped into a plastic bucket, it went back to the zoo hospital for a necropsy to determine the cause of death.
"There's not a lot that can hurt this snake in the wild," Lemm said. "Just a golden eagle and maybe a king snake."
Lemm and Browne have followed No. 27 for two years, and they feel the loss. But the data they've collected from No. 27 could contribute to the red diamond's future in San Diego.
"People need to know that where their new home is used to be the snake's territory," Browne said. "If it shows up in someone's garage, it may be better to move it to a nearby location."

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