Indiana Bats and Wind Farms
The ridge top habitat of areas found in the Alleghany Mountains do not particularly match the topographic characteristics described by the US Fish and Wildlife Service (USFWS) of known Indiana bat summer maternity roosts and foraging areas. The USFWS describes the Indiana bat’s summer foraging area as riparian, bottomland, old fields, and pastures with scattered trees. In addition, existing maternity colonies and foraging areas such as those in Pennsylvania, Vermont, Iowa, Indiana, and Illinois are clearly not located in ridge top terrain. The USFWS also uses the phrase “upland forest” to describe Indiana bat summer habitat, which is rather vague and technically encompasses ridge tops. While it would seem unlikely to find an Indiana bat summer maternity roost or foraging area at the summit of such windswept ridges given the elevation and habitat, it cannot be ruled out since only one Indiana bat maternity roost is known between New York, West Virginia, Maryland, Virginia, and Pennsylvania. As a result, there is no information on what types of maternity roosts Indiana bats in the eastern part of their range may utilize in a large continuous upland forest environment. Without known roosts or foraging areas, very little topography can be excluded from consideration in the Appalachian mountain chain.
The procedure for investigating summer bat habitat is already well defined. Presently the accepted method to is to systematically survey the area in question with mist nets between June 7 and August 1. (The USFWS recommends netting between May 15-August 15, but in the ridge top environment a shorter season may be more suitable due to weather extremes.) By exceeding the USFWS level of effort for summer mist net surveys, it will be possible to conclude whether a colony of Indiana bats use the area sampled.
Indiana bats may choose an abandoned deep mine, a natural cave, or in a deep sandstone crack complex in which to hibernate. Hibernation sites are critical to the species survival. The season may last from September-April in select underground chambers with the proper temperature and humidity. Bats may be vulnerable to nearby wind facility development especially in the fall when a large amount of bat activity occurs in late August through October, in addition to the usual spring and fall migration described in the next section.
A direct internal investigation of hibernation sites is usually best in order to assess the quality of the site and to inventory any bat species present. This type of survey is most often done January through March. A site may only be partially surveyed by humans, and many sites are impossible to enter at all. For these cases a fall live trapping survey lasting several nights can be done to sample the species that are using the site. When possible, both an internal survey and fall trapping should be used to determine the quality of a hibernation site.
Little to nothing is known on the potential impact wind farms may pose on foraging or migrating Indiana bats. A number of Indiana bat hibernaculms are known in or within easy migratory distances of the Appalachian Mountains. Their migration patterns and summer roost areas are for the most part unknown. To this date, only five spring Indiana bat migration studies at four hibernation sites have ever been attempted. One additional migration route was generally determined by a band recovery in the Midwest. Four of the five known migration paths of Indiana bats in the United States are along north-south alignments, making it conceivable that these bats may use a north-south topographic feature such as a ridge top as a migration path. Previous work from 2001-2003 in Pennsylvania and New York found migrating Indiana bats using ridge tops as temporary roosts, foraging areas, and shortcuts. Indiana bats appeared to do most of their major migration between dusk and 1 AM. Additional observations suggest that these bats appear to stay at altitudes at or under the canopy, near natural cover, and often use obvious paths such as utility right of ways to efficiently pass steep ridges and large tracts of forest. To minimize Indiana bat mortality when migrating, it may be ideal to keep cover from encroaching on wind plants and avoid placing turbines near maintained utility right of ways that cross over mountains.
There is concern for a number of other bat species as well. The Small footed bat (Myotis leibii) is a state threatened species in Pennsylvania that no summer studies have focused on. In 2003 three bats of this type in New Hampshire were shown to make extensive use of ridge tops for foraging and roosting during a significant portion of the night. Also of concern is the large number of red bats (Lasiurus borealis), hoary bats (Lasiurus cinereus), and eastern pipistrelles (Pipistrellus subflavus) recently reported dead at wind farm facilities in West Virginia. It is difficult to gauge the vitality of these elusive species. Without any realistic solution for minimizing impacts to migratory animals, an increase of wind plants in the future will contribute to their decline.
Bat Conservation and Management, Inc. believes there are solutions to maintaining operation of wind facilities while minimizing incidental wildlife kills. Very little information exists in this regard and a large amount of data must be gathered at existing and planned turbine sites in order to make informed recommendations. Presently there are at least two general studies that are vital to the investigation of bat and wind facility interaction.
1) How bats encounter wind turbines. A protocol for systematically surveying established wind turbine sites for bat mortality spring through the fall is vital. Data could be collected studying bat kills relating to turbine speed, weather, and season. Electronic acoustic monitoring can record bat activity and compare the amount of activity to mortality. Bat calls can be identified at least to genus and compared with actual mortality counts to obtain the full picture of bats passing by turbines. It should also be determined if turbines or blades emit ultrasonic noise at certain times that may attract bats.
2) When bats migrate. Vertical and horizontal radar can be used to observe migrating bats as they interact with wind facilities. Timing of the year, timing of the night, changes in migration patterns after a facility is online, changes in volume of bats passing by, and the altitude of different species of bats are just some of the elements which can be studied. Electronic monitoring should also occur at proposed wind facility sites to determine if the project area is actually located on a major migratory route; it is easily conceivable that a particular site may not be along a major bat migration route at all.
In summary, it is possible to determine the peak of bat migration over any specific area in the Appalachian Mountains. Spring and fall migration dates can be determined for the different geographic regions in the Mid-Atlantic States, or even on a site-by-site basis. A thorough study of bat mortalities, turbine speed, and nightly peak bat activity may reveal when turbines are least likely to contribute incidental kills. Ultimately a solution to reduce the likelihood of incidental Indiana bat kills during migration may be for certain wind facilities to reduce turbine speed during specific hours of the night under certain weather conditions during specific spring and fall migration periods.
Bat Conservation and Management, Inc. is capable to conduct the projects briefly described above and would be happy to satisfy the recommendations of the U.S. Fish and Wildlife Service, any state agency, or private concern. The projects can be can be further outlined in detail should a client decide to pursue any study. If you have any questions please do not hesitate to write or call.