Rare frogs take a giant leap for endangered species
Red-legged critters back at Yosemite with help from humans
YOSEMITE >> With no parting glance at their devoted human caretakers, 142 rare red-legged frogs swam to freedom Friday — one small jump for the frogs but a giant leap for the threatened species.
Our official state amphibian, the frogs vanished from these pristine mountain meadows 50 years ago.
This new generation, raised from tadpoles at the San Francisco Zoo and rushed to the Sierra in boxes in the back of an air-conditioned SUV, represents a second chance for the beleaguered creatures.
Each frog wears a tiny microchip, surgically slid under its smooth skin, so that its new life can be electronically tracked from afar.
Already there are signs of success. Biologists have discovered at least 20 clusters of eggs — each holding potentially 2,500 future froglets — laid by females released last year. This is the first documented breeding of the reintroduced frogs, named for their brilliant vermillion legs and belly.
“It’s hugely rewarding,” said Rob Grasso, an aquatic ecologist with the National Park Service, who decades ago first identified a red-legged frog in a pond near a timber harvest project in El Dorado National Forest and who led Friday’s release at Cook’s Meadow. “For me, days like this are huge.”
If the frog populations can be reestablished in Yosemite Valley, it will inspire more releases in other sites, such as Mariposa, Tuolumne and Fresno counties, he said.
Perhaps the day will come, he said, when other precious species can be returned to Yosemite, such as the yellow-legged frog, Yosemite toad and western pond turtle.
Friday’s release was made possible through a collaboration between the National Park Service, Yosemite Conservancy,
San Francisco Zoo & Gardens, U.S. Fish and Wildlife Service, California Department of Fish and Wildlife and NatureBridge.
Over the past three years, the program has reintroduced an estimated 4,000 California red-legged frog eggs and tadpoles and 500 adult frogs, according to the Yosemite Conservancy. Last week, 200 more adult frogs were released in the valley, and 275 will be released in June. The separate releases ensure that they don’t overwhelm a particular site or that a single tragedy doesn’t wipe out an entire generation.
“It’s really gratifying — that after 50 years of absence, we can return redlegged frogs back to the park,” said Frank Dean, president of the Yosemite Conservancy, which donated $130,000 for this year’s project and more than $500,000 for overall aquatic restoration.
All over America, national parks are playing an important role in bringing back long-gone species. Most notable is the return of gray wolves to Yellowstone National Park and California condors to Pinnacles National Monument.
But less iconic creatures
also are returning: Pacific fishers in Mount Rainier, North Cascades and Olympic national parks in Washington; black-footed ferrets in Badlands and Wind Cave national parks in South Dakota; nene geese in Hawaii Volcanoes National Park; and desert pupfish in Organ Pipe Cactus National Monument, Arizona.
The California red-legged frog, the star of Mark Twain’s short story “The Celebrated Jumping Frog of Calaveras County,” persists only in a few isolated ponds in the California foothills. These mountain frogs are genetically distinct from their cousins on the California coast, which are more abundant.
Over time, they’ve faced repeated blows.
The first came in the late 1800s, when they were harvested by the metric ton for high-end restaurant menus.
A second assault arrived with the misguided release of predatory bullfrogs into the reflecting pool at the Ahwahnee Hotel in Yosemite in the 1950s. These big and belligerent bullfrogs quickly spread throughout the valley, feasting on smaller native frogs.
Yosemite Valley was filled with so many bullfrogs that their long and loud drones altered the nighttime soundscape of the park, said Grasso.
The red-legged frogs’
fate was finally sealed by a fungus, introduced from overseas by African clawed frogs used in medical testing.
“That was the nail in the coffin,” Grasso said.
But times have changed. While they still have natural predators — hungry salamanders, garter snakes and great blue herons — they’re now far better protected from human tampering.
Listed as a threatened species in 1996, they’re no longer served for dinner. A massive bullfrog eradication campaign — draining ponds and hunting down tadpoles — erased that predator in 2014.
They’re still at risk for fungal disease. But there are clues that some adults may be resistant, although tadpoles likely are still vulnerable.
Friday’s frogs were conceived 110 miles away in a small private pond on the property of Diane Buchholz of Garden Valley, safe from both bullfrogs and fungus.
Buchholz invited park service biologists to wade through her pond, harvesting eggs from basketballsized clumps. They teased out just a few eggs from each mass, to ensure genetic diversity.
Shipped to the city, the eggs were hatched into tadpoles and nurtured in 300-gallon aquariums at the San Francisco Zoo, fed a slurry of algae and then crickets, worms and beetles as they matured.
At the zoo, their aquariums were designed to replicate everything that is special about Yosemite, except the cliffs and crowds. San Francisco tap water was purified to remove chlorine, then minerals were added to replicate Yosemite’s granite. Lighting changed over time, copying the daily and seasonal shifts of the sun. There was little human contact, so they would retain their natural sense of fear.
“We were really trying to mimic what they would have when they came out here,” said Jessie Bushell, director of conservation at the San Francisco Zoo.
To prepare for Friday’s release, the zoo selected the largest and healthiest. Other frogs, still at the zoo, will come later.
“And we picked a mix of personalities — some are really bold, and some are really shy,” Bushell said. “Hopefully, we’ll have a good portion of them make it through whatever they encounter.”
At 5:30 in the morning, the frogs were packed into bins and loaded into the trunk of Bushell’s air-conditioned white Ford Explorer SUV.
“No stops,” she said, laughing. “We got coffee before we got into the car.”
Under bright blue skies, the bins were carried by zoo staff in a celebratory procession, as tourists stopped to wonder. Then, one at a time, the frogs were dished into Tupperware and eased into the water.
Their long strange trip over, the frogs blinked at the wild expanse. Some cautiously lingered in their tubs. Others gracefully swam to nearby weeds or submerged in mud. A few took bold and brave leaps.
“After 50 years of a manmade absence, they’re back, ” said Conservancy president Dean. “After all the hard work and science, research and donations, this is success.”