In a significant boost for endangered species conservation, nearly 400 northern leopard frogs have been reintroduced into their natural habitat at the Columbia National Wildlife Refuge. These frogs, raised from eggs and tadpoles by the Washington State Department of Fish and Wildlife in collaboration with Northwest Trek Wildlife Park and the Oregon Zoo, were released in mid-August.
Once a common sight across North America, the northern leopard frog has faced drastic population declines in Washington state since being listed as endangered in 1999. The decline is attributed to climate change and the encroachment of the invasive American bullfrog, which preys on native species and competes for resources, explained Marc Heinzman, a conservation manager at Northwest Trek.
“The American bullfrog, a popular pet species, has been moving westward due to climate changes that favor its survival. Unfortunately, these bullfrogs consume nearly anything they can catch, including northern leopard frogs,” Heinzman said.
The impact of the American bullfrog has been severe, particularly for the northern leopard frog. Currently, only one known natural population exists in Washington, at Potholes Reservoir near Moses Lake. Despite their continued abundance in other states, the Washington population is genetically distinct and characterized by unique coloration.
Heinzman emphasized the gravity of the situation, stating, “Our conservation efforts are crucial because once a species is extinct, it’s irreversible. We are committed to preventing the permanent loss of these frogs, especially when human actions contribute to their decline.”
The reintroduction project, which aims to safeguard the species’ future, was made possible by a $304,072 grant. This funding includes $228,000 from the U.S. Fish and Wildlife Service and an additional $76,072 from the Washington State Department of Fish and Wildlife.
The Columbia National Wildlife Refuge was selected for this repopulation effort because it is historically native to leopard frogs but has been unable to support the species independently. The land’s ownership by the U.S. Fish and Wildlife Service also provides better management and protection.
Patricia Valcarcel, a herpetologist with the Washington State Department of Fish and Wildlife, noted, “Our goal is to assist these frogs in returning to their historical habitats.”
To enhance the survival chances of the released frogs and protect them from bullfrogs, the frogs were raised to adulthood in controlled conditions, giving them a survival advantage. “By raising them under human supervision, we ensure that a higher percentage reach maturity, making them more robust and resilient,” Heinzman explained.
A protective fence has been installed around the release site to prevent bullfrogs from entering the area.
The reintroduction initiative, which began in 2019, has involved multiple releases of northern leopard frogs. Researchers are still evaluating the most effective methods for raising frogs for reintroduction. This includes an experimental approach where half of the tadpoles were raised in captivity and the other half in semi-natural conditions at the refuge.
Washington State University scientists are collaborating on this project, investigating various factors such as frog behavior, physiology, and predator responses to refine reintroduction strategies. “We are exploring how different early environments impact the frogs’ ability to adapt to stressors after metamorphosis,” said Erica Crespi, a WSU biology professor.
To track the success of the reintroduction, each released frog has been marked with either blue or orange dye, indicating their rearing conditions. Researchers hope this will provide insights into which rearing method yields the most successful outcomes.
Heinzman concluded, “Our ultimate goal is to see these frogs thriving in the wild and to take pride in our efforts to help them recover.”