Collisions

Until 2003, the bat fatalities recorded at wind energy projects during post-construction monitoring were relatively low in number (0 to 6 bats per MW per year) and dominated by a few species (migratory, solitary tree bats such as the hoary, silver-haired, and red bat). The fatalities appeared to occur mostly during the fall migration season (NWCC 2004). The discovery of 458 bat carcasses at a 44- turbine wind project on a forested ridge in West Virginia was unanticipated (NWCC 2004). As a result, the Bat Wind Energy Cooperative (BWEC), a joint effort between AWEA and its member companies, Bat Conservation International, the FWS, and the Department of Energy's National Renewable Energy Laboratory, was formed. BWEC's purpose is to investigate the cause of bat collisions with turbines and to assist the wind industry in avoiding or minimizing the number of collisions. BWEC is currently involved in studies to determine whether high bat fatalities can be reliably predicted based on pre-construction bat activity, as well as other questions relating to bats and wind projects.

In 2005, post-construction fatality monitoring at a wind project in Alberta, Canada found 532 bat carcasses (approximately 13 per turbine; Baerwald 2006). Additionally, there is some evidence that some bat species may be attracted to turbines or changes in the landscape after construction, based on recent studies of bat fatalities at wind projects at eastern forested ridges by BWEC (Arnett 2006). These results indicate that the rate of bat fatalities that will occur cannot be reliably predicted using the methods that have been historically used for baseline studies at wind energy project sites, especially in new geographic regions or habitats where there are no wind developments.

The NWCC also has a subgroup (which includes BWEC staff) on nocturnal methods and metrics that developed the nocturnal companion document to the "Metrics and Methods for Determining or Monitoring Potential Impacts on Birds at Existing and Proposed Wind Energy Sites" (Anderson et al. 1999). This document, "Assessing Impacts of Wind Energy Development on Nocturnally Active Birds and Bats: A Guidance Document" has been published by Kunz et al. (2007).

The following table lists studies that can be used to evaluate collision impacts to bats on wind energy project sites.

Habitat Loss/Alteration

This issue has not been studied in sufficient details to be summarized in this handbook. Developers should stay apprised of new studies and research in this area.

Small brown bat.

Pre- and Post-construction Studies for Assessing Collision Impacts to Bats

Brief Description of Methodology

Purpose

Limitations

Acoustic Surveys (pre- and post-construction)

■ use ultrasonic detectors to record bat calls and software to identify the calls

■ can be used to derive an approximate index of bat use in the vicinity of the detector at a number of wind projects for pre- and postconstruction surveys

■ provides some species composition data

■ the utility of pre-construction call rates in predicting postconstruction mortality has not been proven

■ provides only an approximate index of bat use within the detection range of the detector, but not number of individuals

■ may not permit the identification of all bats to species depending on method used

■ does not provide call rate data in all cases

■ limited by season for migrating bats

Carcass Searches (post-construction)

■ observers conduct standardized searches for dead and injured bats

■ scavenging rates and observer detection efficiency is calculated and used to estimate the number of fatalities occurring, since not all carcasses are found by searches

■ used to obtain empirical estimates of fatality rates resulting from the turbines

■ finding carcasses often difficult

■ expensive and requires searcher efficiency and scavenging trials to provide correction factors for estimating actual fatalities

■ in areas where turbines are located in active agricultural areas often developers must regularly mow areas to improve searcher efficiency, and when this occurs, developers may have to pay for crop losses

■ difficult in forest or shrubland habitats due to vegetation density

■ error estimates can be very large

Genetic (DNA) Testing of Carcasses (post-construction)

■ bat carcasses are subjected to DNA testing to improve species identification

■ can identify species that are difficult to identify by traditional means, such as certain endangered species

■ relatively expensive and require salvage permits and skilled collaborators

Mist Netting (pre-construction)

■ fine, black mesh nets are strung across areas frequented by feeding or commuting bats

■ captured bats are identified to species, sometimes marked, and then released

■ used to capture and identify bats to species where species composition is a requirement

■ not useful for providing an index of use or populations at a site

■ only samples areas where nets can be safely used; does not sample bats flying within the elevation range of the rotor swept area of a turbine

■ labor intensive and permits are required to capture and handle bats

Night Vision/Thermal Imaging

■ visually documents the behavior of bats in the vicinity of wind turbines

■ can be used in combination with acoustic and/or radar surveys

■ provide real time behavioral data on how bats interact with turbines.

■ this type of data may help the scientific community to understand bat mortality, which could in turn support development of successful bat deterrents

■ relatively expensive and do not provide enough information to identify species of observed bats

Portable Marine Radar Surveys

■ use portable marine radars on trailers or mounted on vehicles

■ cover portions of the wind project area from very close to ground level to several thousand feet aloft

■ provide information on passage rates and heights above ground of bats during the day and night

■ these data are available for sites throughout the US for comparison

■ reliable radar data cannot be obtained on nights when insects are abundant or during heavy rains

■ cannot be used to identify species of observed bats

■ bats cannot always be distinguished from birds

5.1.2.2 Mitigation and Monitoring

This section presents many of the current bat mitigation and monitoring techniques that are being used within the wind industry. Appropriate mitigation and monitoring methods vary depending on the specific species of concern, the project location and the regulatory agencies' responsible for review. It is very important that, before making decisions on biological mitigation and monitoring measures for any project, developers educate themselves on the most recent advances and consider engaging a biologist with expertise in the field to guide decision making.

As is the case with birds, wind project siting is crucial to minimizing impacts to bats. It is thought that avoiding siting wind power projects near caves or other sites used by large numbers of bats (such as roosting, hibernation, nursery colonies) can minimize fatalities. Another mitigation measure to minimize potential impacts to bats is to avoid the siting of projects near open water. Open water is particularly important to bats, especially in arid areas as it not only provides drinking water but is a significant source of insect prey.

Aside from siting turbines to minimize collisions, other mitigation methods are currently being studied in relation to minimizing migratory tree bat fatalities. For example, during operation, shutting down turbines on Appalachian ridges (and possibly other eastern sites) on nights with low winds after the passage of frontal systems during the bat migration season appears to be a potentially effective means of minimizing fatalities. This conclusion is supported by findings of a BWEC study (Arnett 2005). However, the effectiveness of this method needs further investigation, and careful consideration must be given to the impact on the project's viability. The BWEC is also testing a system that may deter bats from frequenting wind farms by broadcasting sounds at a frequency and volume that cause bats to avoid the area. This deterrent system is in the preliminary development and testing stage and is unlikely to be available in the near future.

Developers may also consider a financial contribution to research on the interactions of bats and wind turbines in the areas where there is concern about the number of migratory tree bat fatalities. In areas where colonial bats may be at risk, protection of hibernacula and nursery colonies is an additional option to consider as mitigation. Other habitat important to bats also may be preserved or enhanced as form of mitigation.

Renewable Energy 101

Renewable Energy 101

Renewable energy is energy that is generated from sunlight, rain, tides, geothermal heat and wind. These sources are naturally and constantly replenished, which is why they are deemed as renewable. The usage of renewable energy sources is very important when considering the sustainability of the existing energy usage of the world. While there is currently an abundance of non-renewable energy sources, such as nuclear fuels, these energy sources are depleting. In addition to being a non-renewable supply, the non-renewable energy sources release emissions into the air, which has an adverse effect on the environment.

Get My Free Ebook


Post a comment