Management Strategy for Bridges with Townsend's Big-Eared Bat (Corynorhinus Townsendii) Colonies

Focus Area

Wildlife & Ecosystems


Natural Resources






2-3 years

Research Idea Scope

Bats are an indispensable natural resource. Notably, they consume enormous quantities of farm and forest insect pests, saving the agricultural industry millions in lost products. Unfortunately, more than half of <st1:country-region w_st=”on”><st1:place w_st=”on”>America</st1:country-region>’s bats are endangered or declining in numbers as a consequence of the continuing loss of natural roost sites in caves and large snags. Bridges and culverts now appear to be the man-made surrogate of natural bat habitat. For example, at least 12 of the 15 bat species in <st1:state w_st=”on”><st1:place w_st=”on”>Oregon use bridges and culverts either as day or night roosts. Use of the interior spaces of box-beam bridges by Townsend’s big-eared bat (TBEB), has been documented in <st1:state w_st=”on”>California and <st1:state w_st=”on”><st1:place w_st=”on”>Oregon.  TBEB is listed as a sensitive bat species in <st1:state w_st=”on”><st1:place w_st=”on”>Oregon and other states, and federally listed as a species of concern throughout their range. Understanding the extent of this use and the specific bridge characteristics and conditions that provide roosting habitat for TBEB and other bat species is fundamental to insuring these conditions can be replicated when bridges are replaced. Once the conditions and habitat parameters are described or quantified, this information can be applied to designing and testing modifications to provide effective bat habitat to new replacement bridges

The objectives of this study are to: 1) Conduct surveys of ODOT owned box-beam bridges in late 2008 or early 2009 to determine bat species associated with box-beam bridges and specific bridge conditions associated with bat use (eg solar exposure and internal temperatures) 2) Determine nature of bat use (e.g., breeding colony, day roost). 3) Statistically analyze differences in bridge characteristics and placement between box-bridges used and not-used by TBEB and other bat species. 4) Provide ODOT with the data and results, and identify mitigation measures for when bats will be disturbed or displaced during construction/maintenance projects. 5) Using the survey data, work with bridge engineers to design and test bridge modifications that can be applied when box-beam bridges are replaced (2009-2011) 6) Provide a guidance document for bridge designers, DOT’s, and others, addressing survey protocol, requirements of bat species that use hollow space habitat in bridges, and bat-friendly designs for bridge replacements (2012-2013) Potential partners include the USFS, BLM, USFWS, Portland State University, ODOT, and ODFW.

Urgency and Payoff

It is to the long-term advantage of DOT’s to protect TBEB’s and other sensitive bat species that utilize highway structures because listing of new species as threatened or endangered results in increased environmental regulatory requirements for construction/maintenance projects. Additionally, if DOT’s pro-actively integrate bat management into transportation projects, it will generate trust between transportation agencies and the environmental regulatory community, a desirable situation for the timely completion of projects. 

Suggested By

Simon Wray, Oregon Dept. of Fish & Wildlife, Telephone: (541) 388-6444 x 221

[email protected]