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Insects: They're what's for dinner
ODOT saved bat habitat in the new Curtis Creek bridge design
ODOT saved bat habitat in the new Curtis Creek bridge design
Imagine a world swarming with mosquitoes and other small, pesky insects. In that world, it would be humans for dinner. But in a world with bats, insects are the happy meal. Bats are a vital part of the ecosystem because they eat thousands of bugs every day.
Unfortunately, bat populations are declining almost everywhere. In the northwest, many species are listed as sensitive by the Oregon Department of Fish and Wildlife. The agency uses this designation to encourage voluntary actions that will improve species' status or to develop conservation strategies once threats to species are identified.
ODOT is an active partner with organizations throughout Oregon that are doing good things for the environment and wildlife. Knowing that bridges are exactly the type of habitat in which bats roost, ODOT saw bridge program construction projects as a way to contribute to bat conservation. Two replacement bridges near Eugene provided the most recent opportunities.
"When construction began on the bridges at Curtis Creek and Oakhill, we saw the perfect chance to partner with the U.S. Fish & Wildlife Service to directly impact bat conservation in Oregon," said Geoff Crook, environmental program manager for the OTIA III bridge program.
Curtis Creek is similar to other bat habitats ODOT has provided in that it uses the space between existing bridge girders. At Oakhill, the team is using the bridge’s crash wall to create a new habitat.
Before construction began at Curtis Creek, 12 Townsend's big-eared bats were observed on the north end of the old bridge in a gap between the two parallel structures. During the design phase, the ODOT team worked with David Leal of USFWS to determine options to replace the existing bat habitat.
"We examine bridges before construction begins to look for evidence of bats, because they use bridges during the day and evening for roosting," said Leal. "Then ODOT can recreate habitat that will not interfere with future maintenance on bridges."
To build the new bat habitat, crews erected insulated plywood walls on 2-foot by 4-foot frames. Attached to each plywood wall is quarter-inch concrete backing board that serves as a rough surface for the bats to hang from. The walls were placed between the bridge girders to create open spaces that are very similar to those in the previous habitat. The Curtis Creek habitat was specifically designed to accommodate Townsend's big-eared bats because they are attracted to open spaces rather than to the narrow crevices that most other bat species in Oregon favor.   
The approach at Oakhill is quite different. Before construction began, biologists found no evidence of bat colonies at the bridge site. However, because it is near the Fern Ridge Reservoir in a wetland area with an abundance of insects, ODOT saw the possibility of future bat habitat.
The Oakhill Bridge is a poured-in-place box girder structure, which leaves no spaces for the bats to move to during cold weather. The project team saw this shortcoming as an opportunity to try something new, at no cost to the state. 
ODOT took advantage of a crash wall that protects the end bent of the bridge against train derailment. Opposing concrete panels that are secured to the top of the crash wall create a large cavern in which bats can move up and down to thermoregulate away from cold drafts or hot spots.
"The new structures that create habitat for future bat use are examples of our commitment to continuous improvement during construction projects," Crook said. "We expect to complete the new type of habitat at Oakhill by the end of December 2010 and then follow up next year to see if any bats have taken up residence there."
Because bats already use existing bridges, ODOT directly contributes to maintaining the Northwest bat population. By replacing the Curtis Creek and Oakhill bridges near Eugene, the agency is sustaining an existing colony of sensitive bat species and potentially creating new ones.
"With ODOT’s help, we hope to someday remove some of the northwest bat species from the sensitive species list," Leal said.
The world is fortunate to have bats in it, because in that world, the insects will always be dinner. 
More than two-thirds of bat species hunt insects, which include many of the most damaging agricultural pests. A single bat can eat up to 1,000 mosquito-size insects in an hour.