Spotlight on the Oregon Spotted Frog
For more than 20 years, no one reported seeing an Oregon spotted frog in the entire state of Washington. Once found from British Columbia, Canada, to northeastern California, it seemed they had vanished, victims of habitat loss, changes in water quality, invasive non-native bullfrogs, and other causes. But in 1990, a biological survey found the first Rana pretiosa verified since 1968 in Western Washington. Six years later, the area where they made the discovery was put under the protection of the U.S. Fish and Wildlife Service. This area is known as the Black River Unit, managed as part of the Nisqually National Wildlife Refuge Complex.
The frogs have black, irregular splotches on their backs with white spots within the splotches. Their eyes are greenish-gold. Compared to the more-common red-legged frogs, they have shorter snouts and shorter legs and toes with more webbing on the hind feet. They like where they live, generally sticking close to home and not traveling very far.
Oregon spotted frogs lay egg masses in February and March. The temperature of the water dictates when eggs are laid, with 8 degrees Celsius (46.4F) being prime. Egg masses are found in open or lightly brushy, shallow wetlands. There may be a wider range of spots the frogs like to use, including thick wet brush where humans find it hard to access for surveys.
The refuge monitors sites and manages breeding habitat in part by mowing and grazing. Invasive reed-canary grass can choke out good frog habitat if left unchecked. Since reed canary grass is nearly impossible to eradicate, so we manage it instead by mowing. We mow in autumn before the ground gets too soft from rain for the tractor. Mowing at this time prevents the grass from dying during winter and forming a standing mass. Instead, it re-sprouts short and green and offers food for waterfowl. This short form also lets the sun shine into the shallow water, warming it for February frog egg-laying. Frogs are able to use the managed habitat before the grass grows several feet tall by mid-summer.
One egg mass is laid for each female, fertilized by one or two males. There may be 550-900 eggs in each mass. Masses are often laid together in the same area, forming a cluster. Because they prefer shallow water, there’s a risk that the site they use could dry up if the weather doesn’t cooperate; or the egg masses could freeze. The refuge has a permit in case of bad conditions to move egg masses or to make emergency habitat modifications, like creating a little water channel or removing grass clumps.
The hydrology of the Black River area is “flashy”—meaning the shallow water can change a lot in a short time. Frogs may lay eggs in a wet place that a week or two later is dry. Part of the problem is drainage ditches, used to convert the original wetland into pasture. Beavers are a real benefit in this kind of landscape. They can change the habits of a creek and encourage more spreading and flooding, which is good for frogs. Their dammed ponds hold water more reliably, and also hold back encroaching trees, maintaining the open habitat spotted frogs prefer.
Drainage ditches are certainly not the only way humans have changed the hydrology of the Black River. The Black Lake Ditch was dug in 1922, diverting water from the lake into the Percival Creek watershed. This changed the water flow for the Black River watershed, draining agricultural land south of the lake. Much of the water flowing into the Black River now is from groundwater rather than from the lake.
Culverts and bridges, too, have created barriers to water flow and wildlife movement. County engineers are working with Service staff to look at replacing culverts with better designs.
Another way to maintain good frog habitat may enlist the aid of cattle. Cattle owners on neighboring property use fences to control where they want their cattle to graze. “Flash grazing” is when cattle are let into frog territory for a few weeks to chew down the grass where it’s too wet for tractors to mow.
There could also be a connection between frogs and elk. Elk create trails and wallows that hold water in winter. And they eat brush, helping to maintain the open, wet areas spotted frogs prefer.
Good habitat keeps the Oregon spotted frog going, but managing like bullfrogs is also important. American bullfrogs belong east of the Mississippi River, but were introduced to waterways in the West in the early 1900s. They thrive in part by eating other frogs and their eggs, as well as almost anything else they can get into their gaping mouths.
Bullfrog control is essential for protecting Oregon spotted frogs. The refuge hires seasonal bullfrog technicians to work nights, spotlighting bullfrogs and dispatching them with gigs and air rifles. They also set out audio recorders that capture sound. A computer program helps search for bullfrog calls and gives an idea of where the invaders may be located.
The mission of the U.S. Fish and Wildlife Service begins with “working with others.” It is working with others that gives the Oregon spotted frog its best shot at survival. From county engineers to biologists at state and federal agencies, from frog-giggers to farmers to fascinated volunteers, and from beavers to cows, it takes a whole network of effort. As we gain more understanding of the needs of this unique amphibian, we learn about the ecosystem of which it, and we, are a part.
