Two hundred and twenty-three Mountain Yellow-legged Frogs went back to the San Jacinto Mountains this summer, and the people who put them there had been watching them since they were tadpoles.
Birch Aquarium at Scripps Institution of Oceanography released the frogs into creeks in Southern California across two separate trips in August. It is the aquarium’s second successful reintroduction of the species, and it brings the total number of frogs Birch has returned to the wild to more than 440.
It was incredibly exciting to be part of another successful release of Mountain Yellow-legged Frogs. After watching these frogs grow from tadpoles into healthy juveniles, there’s something especially rewarding about seeing them take that final leap back into their native habitat.
Sean Bruce, Assistant Curator of Fishes and Invertebrates, Birch Aquarium at Scripps
How a frog gets from a tank to a creek
The animals arrived at Birch as tadpoles last summer, handed over by the San Diego Zoo Wildlife Alliance. They spent the year growing up behind the scenes, out of public view, in conditions built to get them to a size and condition where a creek is survivable rather than fatal.
Then they went out in two groups, deliberately, to two different places. Spreading a release across sites is how you avoid putting a year of work into one creek and one bad season.
The first trip, in early August, took roughly 74 frogs to a creek near Idyllwild. The second, a few weeks later and a few miles down the road, took 149 more to another creek. Researchers from the San Diego Zoo Wildlife Alliance and the United States Forest Service came along on both. The Wildlife Alliance added two more frogs and 170 tadpoles of its own to the second release.
The part that tells you it is working
At the first site, the team found adult frogs already living there. Not new arrivals. These were animals the San Diego Zoo Wildlife Alliance had released years earlier as tadpoles, now grown up and holding a creek on their own.
The researchers managed to tag one of them, which means they can follow that individual frog for years.
Spotting wild frogs at one of the release sites was especially meaningful, as it was an encouraging sign of a healthy habitat and gave me hope that our newly released frogs can thrive there, too.
Sean Bruce
That is the whole test of a reintroduction program, and it is easy to miss. Releasing animals is not the achievement. Finding animals you released a few years ago, alive, in the place you left them, is the achievement. Everything before that is a hypothesis.
Why this frog needed the help
The southern mountain yellow-legged frog, Rana muscosa, was once common in the streams of Southern California’s mountain ranges. It is now federally endangered, hit by a combination of disease, introduced predatory fish, drought and habitat loss, and reduced to a small number of isolated populations.
Isolated populations are the specific problem. A frog population cut off from every other frog population cannot be rescued by its neighbors after a bad fire or a dry year, and it slowly loses genetic diversity with nobody to trade with. Putting animals back into creeks across a mountain range is an attempt to rebuild the network, not just the numbers.
The recovery program behind this work is a long one and it is crowded, in the good way. Alongside Birch Aquarium and the San Diego Zoo Wildlife Alliance, it involves the United States Fish and Wildlife Service, the United States Geological Survey and the California Department of Fish and Wildlife. Their shared goals are to improve the genetic diversity of both the captive and wild populations, sharpen the reintroduction methods, and grow the wild population.
The San Diego Zoo Wildlife Alliance has been an amazing partner, and I’m incredibly proud of the work we’ve done together to support this important conservation program for our region’s native wildlife.
Sean Bruce
What you can see
Birch Aquarium keeps this work in front of visitors rather than hidden behind it. The Imagine Wild: Mountain Yellow-legged Frog exhibition, presented by The Lodge at Torrey Pines, is built around the recovery effort and the partners running it.
More than 500,000 people visit Birch Aquarium each year, along with over 40,000 students from pre-kindergarten through high school. Those admissions are what keeps a room full of endangered tadpoles growing quietly in the back of the building for a year at a time, until the summer somebody drives them up a mountain and lets them go.
Researchers will be back at both creeks several times a year, counting.
