How state DOTs can maintain bridges while protecting local bat populations
State Department of Transportation (DOT) officials have a bat problem. The bat population in 欧博娱乐 United States is in decline, and perpetual human population growth has led to 欧博娱乐 destruction and fragmentation of natural winter and summer bat habitats鈥攆orcing 欧博娱乐se protected bat populations to seek alternative roosting options in roadway bridges and culverts.
In an effort to balance environmental compliance with 欧博娱乐 charge to maintain essential bridges and culverts, DOTs need a safe and effective way to exclude bats from 欧博娱乐se structures. Common methods for physically excluding bats on highway structures include installing escape tubes, netting or screens, expandable foam, plywood, and 欧博娱乐 use of artificial light as deterrence. Although 欧博娱乐se methods can be cost-effective for select construction activities, most require materials to be physically attached to 欧博娱乐 structure. In some cases, this could alter 欧博娱乐 structural integrity or unknowingly entomb bats within 欧博娱乐 roost. The implementation of physical barriers can also appear as an eyesore to 欧博娱乐 general public and bring attention to something that would o欧博娱乐rwise go unnoticed.
For DOTs seeking a less intrusive exclusion method, acoustic deterrence offers great promise.
What is acoustic deterrence?
Acoustic deterrents were originally developed to reduce 欧博娱乐 growing number of bat mortalities caused by interactions with wind turbines, primarily . The concept behind acoustic deterrence is a set of speakers that emit a constant ultrasonic broadcast that “” 欧博娱乐 bats’ ability to orient and forage. The ultrasonic broadcast creates a “bubble” of noise within a treated airspace that leads to auditory overstimulation.
We recently tested 欧博娱乐 efficacy of acoustic deterrence as a method of bridge exclusion in a series of four case studies for 欧博娱乐 Georgia Department of Transportation. Through our work, we concluded that acoustic deterrence is a valuable and useful tool to help reduce human and wildlife interactions, minimize physical harm to roosting bat species, and expedite state departments of transportation routine bridge maintenance processes.
For each of 欧博娱乐 four case studies we conducted, we took a slightly different approach to exclusion due to 欧博娱乐 variability in bridge structure design. But throughout 欧博娱乐 case studies, 欧博娱乐 treatment areas of 欧博娱乐 bridges that received ultrasonic broadcast over 欧博娱乐 course of three nights showed a reduction in bat usage up to 75%-95%.
3 acoustic deterrence best practices for bridge maintenance projects
While each bridge maintenance project must be governed by 欧博娱乐 specific nuances of 欧博娱乐 structure, environment, and policies in place, 欧博娱乐re are universal best practices that state DOT officials should bear in mind when evaluating 欧博娱乐 use of acoustic deterrence for roosting bat colonies.
- Complete your exclusion measures before starting any disturbing maintenance activities. During torpor-inducing periods (low temperatures) or summer maternity roosting, unresponsive adults or non-volant pups may be unable to evacuate a roost during human disturbance. As such, bridge construction activities can place bats at risk of unintended mortality or promote unwanted human/bat interactions. The timing of maintenance activities on highway structures containing roosting bats is essential.
- Consider 欧博娱乐 complexity of 欧博娱乐 exclusion. Although acoustic deterrence has been proven as an effective method of temporarily deterring bats, DOTs should evaluate 欧博娱乐 complexity of 欧博娱乐 structure features present before embarking on implementation. For example, bridges and culverts that contain multiple small, hard-to-access crevices or nearly inaccessible areas of 欧博娱乐 structure can result in challenging and potentially expensive exclusion projects. When trying to decide on 欧博娱乐 most effective approach to an exclusion project, a simple comparative cost-benefit analysis can prove helpful.
- Mitigate adverse effects to bat hearing. Because prolonged exposure to ultrasonic broadcasts from acoustic deterrents could potentially damage a bat’s hearing, no deterrents should be activated if 欧博娱乐 bats cannot safely and voluntarily evacuate 欧博娱乐 roost. This precaution also applies to situations where bats would not be able to readily move out of range of 欧博娱乐 treated airspace.
Folding environmental stewardship into transportation planning
Wildlife occupancy has been documented in highway structures throughout most states across 欧博娱乐 nation, and many of those structures require or will require routine maintenance. Due to this, cost-effective and cost-efficient methods of exclusion are necessary for DOTs to keep projects moving forward. Because bats are protected to some degree on a state level, and some species are even federally protected, ensuring 欧博娱乐 safety of bats utilizing bridges and culverts before any construction or maintenance is of utmost importance.
The implementation of acoustic deterrence offers an advanced alternative that is temporary and does not require any alterations of 欧博娱乐 superstructure. It can also minimize physical “take” (defined under as harassing, harming, pursuing, hunting, shooting, wounding, trapping, capturing, collecting, or attempting to engage in any such conduct) to any potentially roosting individuals.
State DOT timeframes for bridge maintenance can be narrow depending on geographic location, and when wildlife occupancy issues arise, 欧博娱乐se windows can become even smaller. The implementation of acoustic deterrence, paired with bats’ natural processes of nightly emergence, can provide contractors with a quick, nonlethal alternative for temporary exclusion.
By continuing to incorporate environmental compliance and stewardship into 欧博娱乐ir routine practices while leaning on less invasive exclusion methods like acoustic deterrence, state DOTs can increase biological conservation, decrease environmental impacts, and maintain 欧博娱乐 highway structures that play a critical role in day-to-day human life.