This is an excerpt from the Third Quarter 2013 edition of the Wind Program R&D Newsletter.
Environmental consulting and engineering firm Stantec is observing patterns in offshore bat activity and species composition in the Gulf of Maine, Great Lakes, and Mid-Atlantic coastal states regions to inform efforts to mitigate potential impacts associated with offshore wind energy development in these regions. Monitoring was initiated by Stantec in 2009 with a 3-year pilot study in the Gulf of Maine and expanded in 2012 to a 3-year multiregional U.S. Department of Energy (DOE)-sponsored study. Now in its second year, the multifaceted research effort aims to test the effectiveness of detecting echolocation signals of bats offshore using specialized monitoring equipment and to document the presence of individual bat species and species groups at a variety of offshore sites over multiple seasons and years. To date, Stantec has monitored acoustic bat activity at 36 sites distributed across the three regions, deploying bat detectors on a variety of lighthouses, offshore towers, and weather buoys, as well as three research vessels from the National Oceanic and Atmospheric Administration (NOAA).
Recording bats' echolocation calls using acoustic detectors has proven to be an effective method for documenting offshore bat activity on a regional level. Migratory and nonmigratory bat species have been detected at every site analyzed to date and include patterns of both resident and migratory bat activity. Bats have been detected from April through November, with activity indices highest in mid-August through early September. A compilation of available data from 44 survey periods collected between 2009 through 2012 revealed that 72% of sites recorded bat activity on more than half the nights in which detectors were deployed for the July 15 to October 15 time period, with only two survey periods (4%) reporting less than 20% activity during that same period.
Although bats have been regularly observed at considerable distances from the mainland, preliminary observations suggest offshore bat activity—particularly that involving nonmigratory species like the little brown and northern long-eared bats—becomes more erratic as the distance from the mainland increases. The fact that offshore activity is not solely restricted to migratory species, such as the silver-haired bat, hoary bat, and eastern red bat, is in itself an important finding. Preliminary observations also indicate much of the offshore use is dominated by seasonal migration activity and that small, remote islands are being used as stopover habitats during migration. Whether offshore structures provide similar functions has yet to be determined.
Stantec currently has acoustic bat detectors deployed at 33 sites, including two NOAA research vessels, and will continue to expand the study through 2014 in each of the three regions. The final analysis, due in the spring of 2015, will include a quantitative analysis of offshore bat activity patterns for the various survey years and regions.
Beyond the DOE effort, Stantec also recently completed a study on behalf of the U.S. Department of the Interior's Bureau of Ocean Energy Management involving a synthesis of information on bats and their potential interactions with offshore wind facilities versus activities tracked on land. The study included a comprehensive literature review, a compilation of offshore and terrestrial acoustic studies along northeastern and mid-Atlantic coastal regions of the United States, and a statistical comparison of acoustic bat activity data gathered from inland, coastal, and offshore sites within that region. The assembled database consisted of over 980,000 acoustic call files collected from 61 sites over 37,614 detector-nights between 2005 and 2012. Data from 33 sites were ultimately used to study whether acoustic activity patterns differed among location types. Bat activity was modeled in terms of simple presence/absence (nightly occurrence) and number of calls (nightly intensity). Bat activity was observed at all inland, coastal, and offshore survey sites, indicating that bats were active offshore at least as far as the most remote detectors. Levels of observed offshore activity were comparable between migratory and nonmigratory species, and migratory bats were about equally as likely to be recorded offshore as at coastal or inland sites. In contrast, nonmigratory bats were less likely to be recorded at offshore sites than at coastal and inland sites. The final results were compiled in the recently released report: Information Synthesis on the Potential for Bat Interactions with Offshore Wind Facilities: Final Report.
Ultimately, Stantec's comprehensive assessment will provide essential information on the prevalence of bat use of offshore space. Based on this, strategic mitigation and siting options may be considered that help avoid or minimize the potential impacts of future offshore wind energy developments on bat species. A side benefit of the multiyear DOE-supported effort is that the collected data will provide important regional background information related to the spread of White-Nose Syndrome, a deadly fungal growth that has claimed between 6 and 7 million bats in eastern North America since it was first noted in 2006.