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It’s pure speculation why the numbers of yuma and little brown bats roosting beneath the 3,000-foot-long pier that spans Chapman Bay at the state Department of Natural Resources site has fallen to roughly 2,000 from the 3,000 of recent years, bat researcher Greg Falxa said.
But Falxa suggests that management decisions this past year at Capitol Lake might have played a role.
The bats arrive as pregnant mothers in the spring, set up shop under the pier, then the majority of them start making the 16-mile round trip to Capitol Lake to feed on insects each night, continuing this feeding behavior into the summer after their pups are born. In late summer, the pups join their mothers on the feeding sojourns to the lake.
According to research by Falxa, it is the longest documented feeding commute undertaken in North America by these tiny bats.
Two things happened in the past year that might have affected the bats.
First, the state Department of General Administration drained the lake last July to accommodate a City of Olympia water utility project along Deschutes Parkway.
“The bats lost their foraging area at a critical time,” Falxa said.
“It was mud out there – it had to have had some effect.”
Second, the lake was drained and back-flushed with saltwater in March in a bid to kill invasive New Zealand mud snails. One of the unintended victims of the drawdown might have been freshwater insects in the lake that provide food for the pregnant bats.
While GA officials conceded last year that the July lake drawdown was done without consideration of the bats, there is less official concern about the March saltwater flush.
“The mud flats never dried out and it was a time of year prior to reproduction of the midges that the bats like to eat,” said Michelle Stevie, a senior program specialist with the City of Olympia storm and surface water program.
However, she said, laboratory results of an insect inventory conducted in the lake after the drawdown are still pending.
Meanwhile, DNR is making progress on a habitat restoration project at the 800-acre Woodard Bay complex, according to project manager Michele Zukerberg.
The site, a former Weyerhaeuser Co. log-sorting and log-rafting operation, includes the pier, a railroad trestle, log booms and creosote-soaked pilings that clutter the shoreline and nearshore areas, altering natural habitat and impeding tidal flows to Woodard and Chapman bays.
But some of the wooden structures have become habitat for wildlife, including bats under the pier, harbor seals on the log booms, and purple martin nest boxes on the pilings.
The habitat recovery plan preferred by DNR would remove about 90 percent of the pilings and the Woodard Bay trestle, requiring relocation of bird boxes; remove about 50 percent of the pier superstructure; leave the vast majority of bat roosting area in place; and retain the seal haul-out areas, Zukerberg said.
The state agency is close to securing money from a $1.1 million state Department of Ecology fund slated for Puget Sound cleanup to commence the Woodard Bay work this winter.
Falxa and other bat advocates fear that partial teardown of the pier could disturb the bat habitat.
Zukerberg said the pier is a major public safety hazard because trespassers keep walking on the deteriorating structure.
“They keep punching holes in the fence – there’s always people out there,” she said.
At the very least, DNR plans to start working on replacement bat housing at Woodard Bay as parts of the pier are dismantled.
Additional funding is needed to build alternative bat roosts, Zukerberg said.
The Woodard Bay bats did receive some help before this year’s roosting season. DNR hired a contractor to reinforce some of the rotting beams in the prime roosting area under the pier.
And a recent under-pier survey by Falxa revealed a lot of baby bats — hairless and roughly 1 week old.
John Dodge: 360-754-5444 jdodge@theolympian.com.
