Puget Sound's biggest bat colony could be big loser of dam-removal project

As dusk deepens over Woodard Bay, a couple dozen adults and children gather on the south Puget Sound shoreline to wait for a fluttery spectacle: thousands of bats emerging from their roosts for the night.

Tiny bats gradually appear a handful at a time, barely visible in the gloom, darting erratically over the water and startlingly close to the visitors.

“One just went right through us!” a child shouts.

“Bat!” another shouts. “One just flew over your head!”

“More and more folks have been showing up. It's become a thing,” said bat biologist Greg Falxa of Olympia.

Each summer, pregnant bats gather just offshore at Woodard Bay, where they give birth and nurse little winged pups while hanging from the remnants of an abandoned Weyerhaeuser Company pier, now owned by the Washington Department of Natural Resources.

“The pier has the perfect little conditions underneath that there's gaps that are the right size, and people can't get out there very easily,” Falxa said. “So it's well protected from humans and animals like cats and raccoons.”

Over the decades, the former log dump has turned into a productive habitat for two species of bats, the Yuma myotis and the little brown bat.

“The colony here at Woodard Bay is probably the largest colony of bats in Western Washington,” Falxa said, “certainly the largest one we know of.”

These bats, like others around the country, are threatened by a deadly fungus. The fungal disease known as white-nose syndrome made its first appearance in the western United States in 2016 in King County and has since been spotted in 10 Washington counties.

In June, the Washington Department of Fish and Wildlife reported finding the fungus on bats in the two latest counties, with bats testing positive near Quilcene and Richland.

Though the white-nose syndrome fungus has landed in neighboring Pierce and Mason counties, the Woodard Bay bats haven’t shown signs of the fungus yet.

But they face another problem.

Every night, these bats born on the underside of a decaying pier depend on another artificial habitat: the 260-acre reservoir in downtown Olympia known as Capitol Lake, backdrop to the state Legislature and the governor’s mansion.

The bats fly 8 miles to the lake nightly for an aerial feast on its 15 species of midges and gnats.

It’s the longest known commute made by Yuma bats anywhere and is quite a distance, especially considering the bats are only about 3 inches long.

“Yuma bats are very specialized feeders, foraging almost exclusively over large, flat freshwater bodies,” Falxa said.

The Washington Department of Enterprise Services plans to remove a 70-year-old dam and turn silt- and weed-choked Capitol Lake back into a saltwater mudflat.

Restoring the estuary would eliminate the bats’ midge buffet.

“The loss of freshwater habitat that supports a foraging base for bats from the Woodard Bay bat colony, however, would be a significant unavoidable adverse impact,” according to the project’s environmental impact statement.

The project, supported by the city of Olympia, Port of Olympia, and the Squaxin Island Tribe, is expected to improve habitat for young salmon in Budd Inlet, just downstream, and kill off invasive species like New Zealand mudsnails and Eurasian milfoil that have proliferated in the reservoir.

“Virtually all of the water quality issues associated with Capitol Lake exist because it is an impounded river. Invasive species, drawn to Capitol Lake’s warm, shallow and stagnant environment, are taking over the lake,” according to the Squaxin Island Tribe’s website.

The Washington Department of Ecology concluded that undamming Capitol Lake is necessary to avoid oxygen depletion from decaying vegetation in Budd Inlet.

State legislators this year approved $7 million for design of the estuary project.

Meanwhile, Washington Department of Fish and Wildlife researchers have been testing probiotics on bat colonies in Chelan, Concrete, and Tenino, a first in the United States.

The hope is that spraying beneficial bacteria inside bat roosts will help bats fend off the fungus that causes white-nose syndrome. Researchers expect the bats, which groom themselves frequently, will ingest the good bacteria and help spread it as they rub against their neighbors.