State wildlife officials moved nearly 200 endangered northern leopard frog tadpoles raised at Northwest Trek Wildlife Park in Eatonville to their new home at the Columbia National Wildlife Refuge in Eastern Washington in late May. The tadpoles will continue growing in secured rearing pens until they are mature enough to hop into the wild alongside 200 additional mature frogs later this summer.

“Northwest Trek Wildlife Park is proud to work with our public and private partners on the northern leopard frog project to restore the wild population,” said Curator Marc Heinzman. “It’s incredible to watch them grow from egg masses to frogs and see them hop back into the wild.”

For four years, Northwest Trek has received northern leopard frog egg masses in the spring from the one remaining wild population at the Potholes Reservoir, collected by Washington Department of Fish and Wildlife (WDFW) biologists. Keepers at Northwest Trek then raise the frogs in a controlled environment, monitoring their water temperature, protecting them from predators, and feeding them. Each summer, keepers and WDFW staff release the frogs back into the wild with the goal of establishing a new population at the Columbia National Wildlife Refuge.

A new strategy

Once abundant throughout North America, northern leopard frogs are rapidly disappearing from their native ranges in Washington, Oregon, and western Canada. The species has been listed as endangered in Washington since 1999.

Successful conservation efforts often involve adapting strategies to identify the best outcomes for recovering a particular species. This year, the nearly 400 frogs currently raised at Northwest Trek will be released back into the wild in two stages.

In May, half were transferred as tadpoles into rearing pens at their future release site in Eastern Washington. The other half will continue to be raised at Northwest Trek until they metamorphosize into adult frogs. The two sets will be released into the wild together at the same location later this summer.

The project’s partners—WDFW, U.S. Fish & Wildlife Service, Oregon Zoo, and Washington State University—are investigating whether transferring the frogs as tadpoles rather than as adult frogs will improve their survival rate.

“The tadpoles will continue to be protected from predators in the rearing pens, but they will be in their natural habitat,” explained Heinzman. “Instead of humans feeding them, they will forage for mosquitoes from the environment around them.”

Tracking success

Each spring, the raised tadpoles are weighed, measured, and tagged with a frog-friendly elastomer dye to better track them after their release into the wild. This year, two colors of dye were used: blue dye for the tadpoles now living at the Columbia National Wildlife Refuge in the rearing pens; orange dye for the ones to be released as fully grown frogs.

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.

Funding for the northern leopard frog reintroduction is provided through a competitive state wildlife grant awarded to WDFW from USFWS’s Wildlife and Sport Fish Restoration program and Potholes Supplemental Feed Route mitigation funds provided by the Department of Ecology.