Activity patterns of bat species at interstate highway sites with and without wildlife underpasses


Jenna Chapman

Faculty Mentor(s)

Kristina Ernest (Biological Sciences)


Roads destroy, degrade, and isolate wildlife habitats. Despite the ecological importance of bats and the effect roads have on bats’ access to foraging, breeding, and roosting habitat, relatively few studies have investigated whether wildlife crossing structures (under- and overpasses) facilitate bat movements in road-fragmented areas in North America. Washington State Department of Transportation has created multiple wildlife crossing structures along Interstate-90 (I-90), a major highway near Snoqualmie Pass in the Cascades. We evaluated species presence and activity of insect-eating bats along I-90 where it intersects with wildlife underpasses to investigate whether bats preferentially cross the highway at crossing structures to avoid traffic. To monitor activity patterns and species composition of bats, we recorded echolocation calls at locations along the highway with and without underpasses and in adjacent forest habitats. We used statistical modeling to examine differences in bat activity between these site types. All bat species detected in the adjacent forest habitats were also detected along the highway. Total bat activity was higher near the highway than in the forest habitats, but did not differ between locations with underpasses and those without. Several factors other than the presence or absence of underpasses could explain these differences. However, our study provides baseline information on bats in the area. We recommend more intensive monitoring to better understand the effectiveness of crossing structures in reducing the impacts roads have on bats.

Keywords: Bat, Activity, Crossing structure, Interstate, Cascades, Acoustic monitoring


7 thoughts on “Activity patterns of bat species at interstate highway sites with and without wildlife underpasses”

  1. Great presentation, Jenna. It was very well organized and easy to follow. Important research! I have a question about the frequency guilds–some species fell into more than one frequency guild. Is that because they use different calls at different frequencies, or another reason?

  2. Hi Lisa, thanks for the comment! Yes, there was one species (Myotis ciliolabrum) that could potentially fall within 2 of those guilds and it does have to do with the frequency of their calls, but not so much because of different calls, more so because the calls they use can vary in frequency. To identify bats based on echolocation calls, one of the various components of the call we look at is whats called the characteristic frequency. This frequency can fall within a certain range of values and for the case of the M. ciliolabrum, the range falls within both the 40kHz and 50kHz guilds. I hope that answers your question! If you would like anymore information, please feel free to reach out.

    1. Unfortunately, I was not able to control for lights due to the highway design. This is because the portion of the highway that has been completed, and where the crossing structures were in place, has a chain-up area with a lot of lights, but the portion of the highway where construction hasn’t been completed yet doesn’t have all those lights. So, by choosing unmitigated sites in the pre-contruction area where structures will be built in the future, I was limited to areas without lights, while the mitigated/underpass sites I had access to were all by lights.

  3. Excellent presentation Jenna. Nice job presenting and explaining your project objectives and discoveries so far!

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