Although
horror movies might lead you to associate bats exclusively with caves, bridges
— especially the concrete kind common in Oregon — also make good bat shelters.
The underside of a bridge is dark and quiet, just the way daytime sleepers like
it. And the concrete mass of a big bridge stores heat, so bats can regulate
their mammalian body temperature by climbing up when it’s cool and down when
it’s warm.
Although
no bat species in Oregon are yet listed as threatened or endangered, bat
populations are declining almost everywhere. ODOT recognizes that rebuilding
bridges throughout the state gives the agency a chance to help bat populations
recover.
During design of the new Whilamut
Passage Bridge, we found local Myotis bat populations living around
the bridge work zone.
Our
project team designed and built eight bat boxes — each providing a quiet, safe
daytime roosting place for bats — and installed them on the southbound bridges over
the Willamette River and the Canoe Canal. Bat boxes on the northbound bridge
have yet to be installed.
The new bat boxes will ultimately
help improve bat populations, which in turn help naturally control insect
populations. Bats love to eat mosquitoes and other pesky critters.
The photos above show
bat boxes installed on the Canoe Canal (top) and Whilamut Passage bridges
(bottom). If you look carefully, you can see narrow openings on the bottom and
side of the box that allow bats in and out of their new home.
A bat roosts by
clinging to a rough-textured bridge beam. Photo courtesy of Diane Winterboer,
APHIS USDA Wildlife Services.
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