BISHOP, Calif. — "She's moving," Becky Pierce said as she rotated a hand-held antenna above her head and listened to the beeping signal from a telemetry scanner.
Using the portable equipment, Pierce had picked up the trail of a female mountain lion that had been captured, radio-collared and released outside of town in the Eastern Sierra last winter. Now, the animal was somewhere very close as the tracking party walked into an aspen and willow thicket alongside McGee Creek in Mono County, about 25 miles north of Bishop.
"She probably has a deer kill in here, and they don't like to move very far from them," Pierce said, stopping every few feet to concentrate on the signal, peer at the moist dirt for tracks or up at the aspen branches for lions. Suddenly, the signal started moving up the steep hillside through the dense forest toward Nevahbe Ridge.
Although the big cat never left the thicket, only about 200 yards long by 70 yards wide, the signal went up and down the hillside through the forest for the next 2 1/2 hours, but the animal was never spotted as she circled around the trackers through the trees and dense brush.
"When we first got here, this lion was within twenty yards," Pierce said. "There were a few times when we were right on top of her. I'm sure she was looking at us through the brush at times, and if we'd known exactly the right place to look, we would have seen her."
Pierce, 27, tracks mountain lions for a living. She began working for the California Department of Fish and Game in November, doing most of the field work for a study of the various factors that limit the size of deer herds. By her own choice, she works seven days a week, often in the field looking for mountain lions or for deer killed by lions or other predators.
If the lion had been found, Pierce, who holds a master's degree in zoology, would have looked for a nearby deer kill, logged some data and then left the cat alone.
The DFG study is testing a concept that challenges accepted wildlife management beliefs about the relationship between deer and large predators. The project, proposed for the next five years, could eventually change the way deer are managed in the Eastern Sierra and other parts of the West with similar arid weather patterns.
For the last 30 years, American wildlife management has taught that the herd size of hoofed mammals--deer, moose, bighorn sheep and others--was determined almost entirely by the amount of forage on their range. It was believed that a herd would naturally grow to the size that the available habitat could feed. Although it was understood that predators were constantly taking some animals, their impact on herd size was believed to be insignificant.
The new theory--actually a revived concept about the role of predators--is that predators can play a major role in the size of herds that have already been reduced by poor forage, disease or other factors.
As a model for the study, wildlife biologists chose a deer population that winters in Round Valley near Bishop. Meager forage, caused by years of drought, has reduced the herd size from 6,000 to fewer than 1,000. The biologists want to gain as complete a picture as possible of the dynamics and behavior of the herd and the effects of predators, forage quality, road kills, hunting and other factors.
"We're trying to determine how a population of large predators will affect a population of large mammals that has been reduced very severely by factors probably unrelated to predation," said Vern Bleich, an associate wildlife biologist for the DFG who is supervising the study.
"Forage production here has improved substantially over the last two years as a direct function of increased rainfall. So the dogma predicts that this deer population will now bound right back all of a sudden. The question we're interested in is, 'Will it bound right back?' We're interested in looking at the concept, 'Can predation limit the recovery of this population?' "
Preliminary findings show that there is an unusually high number of lions in the area.
"There were at least 17 mountain lions in Round Valley last winter in far less than 100 square miles, and that's probably one of the highest densities ever recorded, anywhere," Bleich said. "If there are 17 lions and the deer are present on the range for 30 weeks, and a lion kills a deer a week--that's a lot of deer."
Along with other recent studies, including one by the Alaska Department of Fish and Game, this project could help to shift management efforts in some places away from habitat-improvement projects, such as controlled burns, a common wildlife management practice, for decades.
"If predators are controlling the population, then maybe habitat-improvement efforts are a moot point," Bleich said. "Here, we've got lots of unoccupied habitat right now. If the deer population doesn't respond because of predation pressures, there's no sense in proposing habitat-improvement projects.