Oregon Zoo conservationists working in Washington’s Conboy Lake National Wildlife Refuge may have unintentionally documented a record-breaking bullfrog, which experts believe could weigh upward of 50 pounds.
The American bullfrog — an invasive species known to prey on local amphibians — can be seen lurking behind volunteers as they pose for a group photo following an egg-mass survey at the Conboy wetland.
Oregon Zoo conservation research associate Karen Lewis didn’t notice the well-camouflaged leviathan until a full week after the survey, while reviewing photos with the volunteers.
“We just stood around the computer screen with mouths agape,” Lewis said. “Judging by the frog’s distance from the volunteers and the size of the adjacent vegetation, we believe this individual could weigh in the neighborhood of 50 pounds.”
Bullfrogs typically can grow up to 8 inches in length and seldom exceed 1.5 pounds. The photo is currently being analyzed by wildlife officials.
“This discovery has raised more questions than answers,” Lewis said. “Invasive species are a huge problem for the recovery of a wide range of native wildlife, but clearly the problem is bigger than we imagined.”
The volunteers in the photo had been conducting an egg-mass survey to document populations of the Oregon spotted frog, one of the Northwest species most threatened by non-native American bullfrogs.
With the notable exception of Conboy Lake, Oregon spotted frogs have disappeared from almost every wetland where bullfrogs have invaded. The seemingly “bullfrog-proof” nature of Conboy Lake spotted frogs makes them particularly important to the recovery of the species.
Researchers wouldn’t speculate about whether the Conboy spotted frogs’ skill at evading predators might be an adaptation to sharing their habitat with the freak of nature seen in the photo, which Lewis described as “capable of devouring a cat.”
Since 1998, zoo staff and volunteers have worked closely with biologists at the Washington Department of Fish and Wildlife to document and protect the Oregon spotted frog, which is considered threatened in Oregon, endangered in Washington and Canada, and is a candidate for listing under the federal Endangered Species Act.
The zoo is a service of Metro and is dedicated to its mission of inspiring the community to create a better future for wildlife. Committed to conservation, the zoo is currently working to save endangered California condors, Oregon silverspot and Taylor’s checkerspot butterflies, western pond turtles and Oregon spotted frogs. Other projects include studies on Asian elephants, polar bears, orangutans and giant pandas. Celebrating 125 years of community support, the zoo relies in part on donations through the Oregon Zoo Foundation to undertake these and many other animal welfare, education and sustainability programs.
The zoo opens at 9 a.m. daily and is located five minutes from downtown Portland, just off Highway 26. The zoo is also accessible by MAX light rail line. Visitors who travel to the zoo via MAX receive $1.50 off zoo admission. Call TriMet Customer Service, 503-238-RIDE (7433), or visit www.trimet.org for fare and route information.
General zoo admission is $11.50 (ages 12-64), $10 for seniors (65 and up), $8.50 for children (ages 3-11) and free for those 2 and younger; 25 cents of the admission price helps fund regional conservation projects through the zoo’s Future for Wildlife program. Additional information is available at www.oregonzoo.org or by calling 503-226-1561.