Bonneville Power Says ESA-Listed Oregon Spotted Frog Finding ‘Refuge’ Under Transmission Lines

The threatened Oregon Spotted Frog, which has lost habitat to development, agriculture and invasive species has found refuge in what may seem like an unlikely place: beneath the high-voltage power lines of the Bonneville Power Administration, said the agency in a press release.

The Oregon spotted frog is listed as threatened under the Endangered Species Act.

“Oregon spotted frogs lay eggs in the shallow water provided by wetlands, such as those that exist within many BPA transmission line corridors. Because high-growing vegetation poses a risk to power lines, BPA works to cultivate low-growing native plants that protect wetlands and maintain open-water habitats, all of which are beneficial to frogs,” said the BPA press release.

The Oregon Spotted Frog is the most aquatic native frog in the Pacific Northwest, according to the U.S. Fish and Wildlife Service.

It is almost always found in or near a perennial body of water that includes zones of shallow water and abundant emergent or floating aquatic plants, which the frogs use for basking and escape cover.

Oregon spotted frogs seem to prefer fairly large, warm marshes (approximate minimum size of 4 hectares (9 acres)) that can support a large enough population to persist despite high predation rates and sporadic reproductive failures. Large concentrations of Oregon spotted frogs have been found in areas with the following characteristics: (1) the presence of good breeding and overwintering sites connected by year-round water; (2) reliable water levels that maintain depth throughout the period between oviposition and metamorphosis; and (3) the absence of introduced predators, especially warm-water game fish and bullfrogs.

In Oregon, this frog species is only known to occur in Wasco, Deschutes, Klamath, Jackson and Lane counties, although historically they were also found in Multnomah, Clackamas, Marion, Linn, and Benton, counties. In Washington, the frogs currently occur in Whatcom, Skagit, Thurston, Skamania and Klickitat counties.

Many factors are believed to have caused Oregon spotted frogs to decline and continue to threaten this species, says USFWS, including loss of habitat, non-native plant invasions, and the introduction of exotic predators such as bullfrogs. Over 95 percent of historic marsh habitat, and consequently Oregon spotted frog habitat, has been lost in the Willamette and Klamath basins.

Changes in hydrology (due to construction of ditches and dams) and water quality, development, and livestock overgrazing continue to result in habitat loss, alteration, and/or fragmentation. Non-native plant invasions by such aggressive species as reed canarygrass, and succession of plant communities from marsh to meadow also threaten this species’ existence. Introductions of bullfrogs and non-native fishes have affected this species both directly, by eating them, and indirectly, by outcompeting or displacing them from their habitat.

The majority of Oregon spotted frog populations are small and isolated. These factors make the Oregon spotted frog more vulnerable than large connected populations to random, naturally occurring events, such as drought, disease, and predation, says USFWS.

BPA, said the press release, works closely with the U.S. Fish and Wildlife Service and other agencies to ensure it protects suitable habitat for the Oregon spotted frog and other wildlife living beneath its transmission lines. Methods include reducing the unintentional injury of frogs from equipment, hand mowing or cutting non-native vegetation and carefully planning spot herbicide use.

 “The agency’s practice of maintaining healthy plant communities along its rights-of-way and limiting the use of herbicides decreases maintenance costs and improves power system reliability.

The Oregon spotted frog isn’t the only species that thrives in the improved habitat. BPA’s techniques promote the growth of low-growing shrubs and flowering plants that are critical for imperiled honey bees and other pollinators.”

The ESA-listed frog once lived in open wetlands, lakes, ponds, streams and occasionally slow-moving rivers from northern California to British Columbia.

Today, the threatened frog can still be found in some river basins in Oregon, Washington and British Columbia, but scientists have not documented the animal in northern California for more than a century.

The Bonneville Power Administration, headquartered in Portland, Ore., is a federal power marketer that sells wholesale electricity from 31 federal dams and one nuclear plant to 142 Northwest electric utilities. BPA delivers power via more than 15,000 circuit miles of lines and 261 substations to 475 transmission customers. In all, BPA markets about a third of the electricity consumed in the Northwest and operates three-quarters of the region’s high-voltage transmission grid.

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