Work is scheduled 9 a.m. to 2 p.m. Tuesday, Jan. 22 and Wednesday, Jan. 23. Caltrans staff in Jamestown say traffic on the bridge will be restricted to one lane and motorists should expect 15-minute delays

Motorists can expect delays next week on northbound and southbound Highway 49/108 at Woods Creek Bridge, where Caltrans workers plan to install temporary measures to prevent bats from roosting under the bridge or inside crevices on the bridge during a repave project planned this summer.

Yuma myotis bats can come in colonies as large as 10,000 bats, and some of them are known to roost under and inside Woods Creek Bridge when they come to Tuolumne County. They are listed as a species of special concern, not endangered, by the California Department of Fish and Wildlife. Woods Creek Bridge is about one mile south of Jamestown and just north of Bell Mooney Road.

“Right now the bats aren’t there,” Rick Estrada with Caltrans District 10 said Friday. “We don’t want to come to do the work in summer and find out there’s wildlife there. When the new surface is finished, we’ll remove those foam rods so the bats can come back and it will be the same bat house it used to be.”

Tiny fliers with teeth

Yuma myotis bats are common vesper or evening bats. Biologists say they are small compared to some bats, measuring 1.5 to 1.9 inches in head-body length, with wingspans averaging 9.4 inches, weighing about 6 grams or one-fifth of one ounce each, with 38 teeth.

Scientists call them Yuma myotis bats because they were first described from specimens captured near Fort Yuma, in Imperial County in southeast California, across the Colorado River from Yuma, Arizona. A myotis is a mouse-eared bat.

They are nocturnal and thousands of them can also be found roosting in caves, attics, buildings and mines. Yuma myotis bats regularly crawl into crevices and gaps on the exterior of the concrete, two-lane bridge over Woods Creek, according to Caltrans.

Workers plan to use foam rods to seal those crevices and gaps because the bats are living elsewhere or hibernating for winter. According to Caltrans, they typically enter an inactive state from Dec. 1 to Feb. 15 and leave the bridge. This means Caltrans have an opportunity now to install bat exclusion measures without fear of harming the bats.

Basket work

During the work scheduled Tuesday and Wednesday next week, a Caltrans truck will be positioned on the bridge, using a basket to give workers access to spans and underside of the bridge, where they will install the foam rods.

Caltrans and state Fish and Wildlife staff expect the bats that normally roost under Woods Creek Bridge will find new places to roost this spring.

The bridge resurface project will include application of a polyester-concrete overlay this summer. Estrada said the new surface is necessary because there are rough spots on the bridge, water pools in places at times, and transitions between road surfaces and the bridge surface are uneven.

Workers will remove the bat exclusion rods from under Woods Creek Bridge once the paving project is completed later this year, allowing the bats to return to their traditional roost, according to Caltrans.

Critical bridge

Woods Creek Bridge is critical to residents, workers, visitors and the tourism-based economy of Tuolumne County, California Department of Transportation staff said.

A closure of Woods Creek Bridge for any reason would force motorists headed to Big Oak Flat, Groveland and Yosemite to seek detours including Jacksonville Road.

The treacherous, single-lane Wards Ferry Road route to Groveland and Yosemite remains closed this week due to a big rig propane tanker trailer crash last week on the north side of the Tuolumne River, according to California Highway Patrol staff in Jamestown.

Work is scheduled 9 a.m. to 2 p.m. Tuesday, Jan. 22 and Wednesday, Jan. 23. Traffic on the bridge will be restricted to one lane and motorists should expect 15-minute delays. Drivers are being urged to take alternate routes whenever possible during these two days.

Bat facts

California Department of Fish and Wildlife records show Yuma Myotis bats have also been observed in the Stanislaus River basin. Woods Creek is tributary to the Tuolumne River and it flows into Don Pedro Reservoir.

A March 1995 Stanislaus River Basin and Calaveras River Water Use Program threatened and endangered species report showed Yuma myotis bats among at least four bat species confirmed on the Stanislaus River.

Biologists say the Yuma myotis has short, rounded ears, and a pointed tragus prominence in front of the outer ear. The bat’s body has light buff to dark brown fur with lighter underparts.

Yuma myotis bats can be found in the western quarter of North America from Canada south to Mexico, and east to Idaho and Texas, including parts of Montana, Utah and Colorado. They are common up and down California except in the Mojave and Colorado deserts of southeastern California. They are present in mountain ranges bordering the Colorado River Valley, including the Fort Yuma region they are named for.

They like to feed on small flying insects they find with chirps and sound waves and echolocation. They often feed over water sources like ponds, streams and stock tanks. Optimal habitats are open forests and woodlands with sources of water over which to feed. Their favorite foods include moths, midges, flies, termites, ants and caddisflies. Some scientists say Yuma myotis bats are efficient foragers, able to return to roost with a full stomach just 15 minutes after dusk. They can live anywhere from sea level to 11,000 feet, but they’re uncommon above 8,000-foot elevations.

Yuma myotis bats do hibernate in some areas, and they may make short seasonal migrations from higher elevations to preferred places for wintering, according to research cited by California Fish and Wildlife staff. They often form large maternity colonies of several thousand females and young bats, in buildings, caves and under bridges. Warm, dark sites are preferred. Individual bats cluster tightly in the warmest sites when temperatures are low. Boy bats and girl bats mate each fall and produce one baby bat per pair between late May to mid-June. They live a life span of about eight years.

Caltrans routinely does environmental studies in the field while planning projects, Estrada said. The state transportation department took that same approach in 2018 while planning the Woods Creek Bridge project. Studies confirmed bats were using the bridge as a roost. Caltrans staff plan to revisit the area shortly before the work is scheduled to begin, to confirm they’ve accounted for wildlife and that the bat exclusion measures have worked.

Contact Guy McCarthy at or 588-4585. Follow him on Twitter at @GuyMcCarthy.