Bat Counters Work on the Fly in Census for Bridge Project

TOPANGA — Tally takers participating in the first bat census in Topanga learned one thing for sure: why that catch phrase “bat out of hell” entered the language as synonymous with “sudden burst of activity.”

“You can hear all this chittering, like they’re talking about where they are going to go and what they are going to eat, then there is a pause in the noise, then an explosion from under the bridge,” said biologist Rosi Dagit, who led the survey by 22 volunteers Saturday.

“They seem to have a very clear idea of where they are going.”

The bevy of bats flew out from under three wooden bridges so quickly that counters are sure there are more than the 850 they clicked off on hand-held Tally Whacker counters.

“They circle around just once under the bridge and then just explode out of there--just really bolt out,” Dagit said. “Everybody was just clicking so fast.”

The counters used various strategies to avoid missing some bats and counting others several times. The flight path was zoned and several counters were assigned to each zone. Then their tallies were compared.

Biologists learned from the census that there are at least two species of bats in the canyon. They counted during the departure of common Mexican free-tail bats, which sped out of their roosts between 8 and 8:45 p.m. They then discovered big brown bats, which roost under the same bridges but were not counted because they emerge when it is too dark to see them.

Census leaders plan to use night-vision equipment to count the big browns during the next bat census in the fall, when they will also re-count the Mexican free-tails.

The census is being conducted so that “bat crevices” can be built under concrete replacement bridges for the old wooden structures. The county Department of Public Works is paying for the environmental studies so that the bats will not be displaced when work begins on the first bridge next spring.

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News of the unusual bat count stretched all the way to Capitol Hill, where a congressman demanded to know how the bat counters could count bats accurately, given the predicted inaccuracy of counting people for the census in 2000.

The question prompted a flurry of calls from congressional offices to the Santa Monica Mountains Resource Conservation District, which conducted the bat census. The legislators’ aides wanted to know exactly how the job was being done, said Dagit, who could not recall the name of the congressman who set off this odd sidelight to the bat tally.

Volunteer counters were positioned before dark at each of the three bridges, staying very quiet so as not to disturb the bats, which would not fly if they were frightened. The census crew did not even use flashlights, relying on the dim light at sunset.

Leaders of the bat census decline to specify the locations of the three bridges because they fear the bats will be harmed by vandals or disrupted by visitors. But they said there are other wooden bridges in the canyon that also may harbor bats. Counts at the three bridges totaled 150, 200 and 500 bats.

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The census is part of an ongoing project funded by the county Department of Public Works to map and identify all sensitive species of plants and animals in the Topanga watershed. When the project is completed--expected by late summer 1999--computerized maps will be used by county public works employees to assess the environmental impact of any project before it begins, Dagit said. The cost of the $23,000 survey averages out to $1.85 per acre--considered a bargain by environmentalists in return for protecting rare species in the 12,400-acre watershed.

“This is something public works really hasn’t done before,” Dagit said.

She called the degree of accuracy of the bat census “higher than anticipated,” and credited training sessions, along with the enthusiasm and care of volunteers.

Workers will continue to monitor the movement of bats to various bridges throughout the year.