For the fourth time, hundreds of endangered frogs were released into the Columbia National Wildlife Refuge with the intent to revitalize their population.
The nearly 400 northern leopard frogs were collected as eggs by the Washington State Department of Fish and Wildlife and raised from tadpoles by Northwest Trek Wildlife Park and Oregon zoo staff. The adult frogs were released mid-August.
Once abundant across all of North America, the northern leopard frog has been on the Washington endangered species list since 1999. Climate change and the arrival of the invasive American bullfrog from the East side of the country have decimated their populations, said Marc Heinzman, a conservation manager at Northwest Trek.
"(Bullfrogs have) made their way westward over time because they are popular as pets, as well as the climate changes — it's been more hospitable to them," Heinzman said. "Unfortunately, bullfrogs will eat just about anything that fits in their mouth, and that includes these frogs."
The arrival of the American bullfrog has been harmful to many native species, but Heinzman said that the northern leopard frog's populations are alarmingly low, with only one site in the State where they are still found naturally — the Potholes Reservoir near Moses Lake. Leopard frogs remain abundant in other states across the country, but those native to Washington have unique coloration, reflecting their genetic distinctness.
"Whether it's northern leopard frogs or any other species that we work with to try to protect with our conservation efforts, the thing we always try to keep in mind is once they're gone, they're gone for good," Heinzman said. "And we would hate to have them gone for good, especially when it's caused by human activities."
The repopulation effort was funded by a competitive U.S. Fish and Wildlife Service grant of $228,000, which was matched by the Washington State Department of Fish and Wildlife for a total of $456,000.
A new population of wild frogs could act as a safeguard for the species in the state.
"Should something catastrophic happen to the one population that we know of now, we at least have other sites where these frogs can be found and hopefully, the species would not experience a catastrophic loss related to that," Heinzman said.
The Columbia National Wildlife Refuge was chosen for the new population because leopard frogs are native to the area but unable to physically return to on their own.
Furthermore, the land is owned by the U.S. Fish and Wildlife Service, allowing for more control of what is done at the property, department herpetologist Patricia Valcarcel said.
"We're just trying to assist them in getting back to their historic environments," Valcarcel said.
To combat their being preyed upon by the bullfrogs, Northwest Trek handlers raised the frogs from tadpoles to adults. By raising them under human supervision, a much larger proportion of tadpoles are able to reach maturity, and therefore have a "boost," Heinzman said.
"They have a better ability to escape," Heinzman said. "They're just a lot bigger. They're more robust. They're more healthy."
A fence around the release site is meant to keep bullfrogs out of the area as well.
Although the reintroduction project has been ongoing since 2019 and involved three other releases of northern leopard frogs, the best methods of raising frogs for release remain unknown.
Experimentally, half of the northern leopard frog tadpoles were raised completely in captivity, while the other half were raised in pens at the Columbia refuge where they had to forage for their own food. This is part of ongoing research to determine the most effective rearing method, Valcarcel said.
Scientists at Washington State University have also been collaborating on this project, studying frog behaviors, physiology, predator responses and diseases.
"It's a big open question about how that early environment can influence the way frogs respond adaptively to stressors after metamorphosis," WSU biology professor Erica Crespi said.
This research could lead to more effective reintroduction strategies.
Every frog released in this year's batch has been marked with either nontoxic blue or orange dye under their skin depending on where they were raised in order to help researchers determine which group is more successful upon recapture.
"We would just love to see thriving populations of frogs on their own that we can just observe from a respectful distance," Heinzman said, "and be happy about the work that we did to help get them there."
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