Roughly 850 tadpoles, hatched from red-legged frog eggs, were released into the Santa Monica Mountains on Tuesday, marking the first time the threatened species has been reintroduced into the area after a decades-long absence.
“It’s very exciting. There haven’t been red-legged frogs here for at least 45 years, and they’re free here now," said Katy Delaney, a wildlife ecologist with the National Park Service who leads the project.
The three-year-long project is a joint effort among several groups, including the National Park Service, the Mountains Recreation and Conservation Authority, the U.S.Geological Survey, the U.S. Fish and Wildlife Service, state parks and the Santa Monica Bay Restoration Commission.
Growing a frog
The scientists followed protocols from a successful reintroduction performed at Pinnacles National Park about a dozen years ago. Amy Fesnock — who now works as a threatened and endangered species specialist for the California Bureau of Land Management — was a wildlife biologist at Pinnacles and led the initial reintroduction effort.
The exact cause of the species' decline is unknown, but it's believed to have been related to human activity. People ate the frogs in large quantities and introduced invasive predators and harmful fungi that have suffocated many amphibians.
“I feel it’s like a karma thing. If we as humans have done things that I can go back and say this is why this population is not doing well, I think it’s our responsibility to then do things to correct that wrong,” Fesnock said.
In March, Delaney's team transferred about a thousand eggs from a spot in the Simi Hills, one of the three remaining locations in Southern California where red-legged frogs still live. The other two locations are in Palmdale and Santa Clarita.
They placed the eggs within protective mesh enclosures in two locations in the Santa Monica Mountains. Scientists then monitored them regularly, making the rigorous trek to the undisclosed locations multiple times a week.
The tadpoles were fed a diet of organic romaine lettuce, high-protein pet frog food and algae pellets to supplement the algae they gleaned from the inside walls of their enclosures.
The locations are ideal because of their year-round water, protective geologic features and relative lack of invasive species. The majority of the eggs hatched successfully, and biologists raised the tadpoles in the enclosures to keep them safe.
“We want to get them to the point where they are, basically, their head and body are big enough to avoid being eaten by newts," Delaney said on a monitoring trip in early July.
The vast majority of tadpoles survived to the point where they could be released safely. A couple hundred were released into the wild last week, after a minor die-off necessitated evacuating some of the cages earlier than expected.
On release day, the freed tadpoles were swimming around in their mountain pool, appearing to thrive in their new environment.
On Tuesday morning, Delaney's team collected, counted and released the remaining tadpoles.
The tadpoles were released in neighboring pools, in order to provide some measure of redundancy. Each location can naturally support about a dozen adult red-legged frogs.
Upon release, the tadpoles swam to the bottoms of their new habitats and began feeding on the algae growing there.
"It's really cool to see them swim away like that and act normal. They're acting completely normal," Delaney said.
Red-legged frogs live for two years before they begin breeding. In the fall, the tadpoles will be at their most vulnerable stages: newly metamorphed frogs. Next year, the scientists will repeat the reintroduction at even more sites within the mountain range.
For Delaney — who said that she has lost many nights of sleep worrying about the tadpoles — the project has so far been a success.
"They've been doing the right thing this whole time, so we're happy," Delaney said. "Now we just have to make them into frogs."
This story has been updated.