Endangered frogs set to hop into the wild

Nearly 400 mature frogs will soon be released into the wild of the Columbia National Wildlife Refuge thanks to a team of Washington State University scientists and their collaborators.

The goal of the conservation effort is to bolster the native population of endangered northern leopard frogs in central Washington.

WSU biologists Erica Crespi, Caren Goldberg, and Jeff Manning, along with pathologist Allan Pessier are once again partnering with the Washington Department of Fish and Wildlife (WDFW), Northwest Trek Wildlife Park in Eatonville, WA, and the Oregon Zoo on the project.

Once abundant throughout North America, northern leopard frogs are rapidly disappearing from their native ranges in Washington, Oregon, and western Canada; only one population remains in the state of Washington in the Potholes region near the refuge. The species has been listed as endangered in Washington since 1999.

"Frogs play an important role right in the middle of food webs in the environment, as they consume plant matter as tadpoles and insects as frogs, and many predatory species consume them, such as herons, garter snakes, raccoons, and unfortunately, invasive bullfrogs that have dominated leopard frog native wetlands in Washington," said Crespi.

For each of the past four years, Northwest Trek and the Oregon Zoo have received northern leopard frog egg masses collected by WDFW biologists from the one remaining wild population at the Potholes Reservoir. Keepers at the zoos then raise the frogs in a controlled environment before they are released into the wild.

This year, there is a twist-the frogs they raised will be released at the refuge from three development stages: eggs moved directly from the natal site, half of frogs raised at the zoos relocated as tadpoles, and then half as adult frogs. Researchers are investigating whether transferring the frogs from these different development stages influences their survival.

Keeping track

In late May, Crespi and WSU graduate students Jonathan Schafer and Dana Shellhorn helped weigh, measure, and tag all of the tadpoles housed at Northwest Trek and Oregon Zoo with a frog-friendly elastomer dye to better track them after their release. At Northwest Trek, for example, two colors were used: blue for the first wave of tadpoles, orange for the ones to be released as fully grown frogs.

The blue-tagged tadpoles were transferred into rearing pens at the refuge release site located in eastern Washington. Since then, they have been protected from predators but have been learning to forage on mosquitos on their own and experience visual and chemical predator cues in their natural environment.

The other half of the tadpoles-the ones with the orange tag-remained at Northwest Trek where staff have been monitoring the water temperature, protecting the frogs from predators, and feeding them until they all metamorphose into adults.

The blue and orange-tagged amphibians will be released into the wild together at the same location in early August.

Shafer and Shellhorn will be conducting "flight response" assays to better understand whether frogs from each of the release groups differ in anti-predator behaviors, which may be associated with their ability to survive as frogs in the natural environment.

"We've used these assays in the past, and we've shown that captive-reared frogs are less responsive to a person walking towards them at the edge of the pond compared to the frogs from the Potholes Reservoir," said Crespi.

This year, they will test whether experiencing challenges early in life in the natural environment improves predator evasion after metamorphosis. Crespi explained, "If tadpoles in the wild learn the cues from the kinds of predators they will experience later in life, transfer of captive-reared leopard frogs during the tadpole stage may increase their chance of survival after release."

Findings from this project should inform other amphibian reintroduction projects that include captive rearing or "headstarting."

The likely causes of frog decline in the Pacific Northwest include habitat loss and degradation, diseases, non-native species, and climate change. According to WDFW officials, northern leopard frogs are an essential indicator of water quality due to their permeable skin. Improving and conserving wetland habitat will help frogs and other species, ranging from amphibians to waterfowl and deer.

"We are proud to work with public and private partners to restore the on the northern leopard frog wild population," said Marc Heinzman, Northwest Trek curator. "It's incredible to watch them grow from egg masses to frogs and see them hop back into the wild."

Funding for the northern leopard frog reintroduction is provided through the U.S. Fish and Wildlife Service's Competitive State Wildlife Grant (C-SWG) Program, McIntire-Stennis, and matching WSU funds.

This project is associated to Crespi, Goldberg, and Mannings's Community Engagement Award Project that is partnering with the Kalispel Tribe to determine if there are ponds that can serve as potential release sites on tribal property to return northern leopard frogs to this part of their native range.

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