After four years, San Francisco Zoo officials wrapped up a successful reintroduction program Monday by releasing the last of more than 1000 red-legged frogs into Yosemite National Park.
The zoo began partnering with the National Park Service and Yosemite Conservancy in 2015 to reintroduce the threatened frogs back into Yosemite National Park, where they underwent a steady decline 50 years ago.
The park now features an all-time high of 1,073 red-legged frogs, all reared at the San Francisco Zoo.
Jessie Bushell, director of conservation at the San Francisco Zoo, said the moment felt “bittersweet.”
“We have reached our goal, but they have been part of our life for four years. This moment was in our brain for quite a while,” said Bushell.
The introduction of the non-native bullfrog, drainage of water and the proliferation of raccoons have contributed to the disappearance of the red-legged frogs in Yosemite.
“If you release 50 [bull]frogs in an area, they are massive predators and can be problematic,” said Bushell.
However, the red-legged frog quickly adapted to the environment after Yosemite got rid of the bullfrogs, an effort that took 10 years.
After two years in the wild, the Zoo-reared frogs have survived and reproduced, and some have doubled in size, according to data collected by the zoo.
“If they are given the chance, they can thrive,” said Bushell.
Yosemite National Park biologists perform regular night surveys and skin swabs to track potential disease and follow health conditions, while the zoo placed transmitters on 45 of them.
The 999th red-legged frog was the last to get tagged with a transmitter.
“The challenge is to see if they will still do well in the next five years,” said Bushell.
20 red-legged frogs are currently on display for educational purposes in the California Conservation Corridor exhibit at the zoo.