Alternative Energy Draft EA - NASA Visitor Center at Wallops Flight ...

Summer–Fall 2008 Bat Study at Wallops Island
Affected Environment
Between July 15 and October 21, 2008, passive acoustic bat surveys were conducted on Wallops
Island in the area of the proposed wind turbines to document bat activity and identify species that
occur in the area (Appendix B). Four Anabat® acoustic detectors deployed at the proposed wind
turbine site (see Figure 12) collected data over 229 nights of recordings. Two detectors were
placed in an existing 50-meter (164-foot) unguyed tower (the same tower as the “South
Boresight Tower” in the previous sections), which is located approximately 427 meters (1,400
feet) south of the proposed wind turbine site, and two were situated on 10-meter (33-foot) poles
in adjacent marshlands.
A total of 2,140 bat call sequences were recorded during the sampling period. The mean
detection rate of all detectors was 9.3 detections per night. The highest detection rate was 15.9
detections per night, and the lowest rate was 2.4 detections per night. Bat calls were identified to
the lowest possible taxonomic level, and were then grouped into six guilds based on similarity in
call characteristics between some species and the uncertainty in the ability of frequency division
detectors to adequately provide information for this differentiation. The six guilds are described
below.
Unknown – All call sequences with too few pulses (less than five) or of poor quality
(such as indistinct pulse characteristics or background static).
Myotid – All bats of the genus Myotis. While there are some general characteristics
believed to be distinctive for several of the species in this genus, these characteristics do
not occur consistently enough for any one species to be relied upon at all times when
using Anabat® recordings.
Eastern red bats, eastern pipistrelles, evening bats (RBEP) – These three species can
produce calls distinctive only to each species. However, significant overlap in the call
pulse shape, frequency range, and slope can also occur.
Big brown/silver-haired bat (BBSH) – These species’ call signatures commonly overlap
and were therefore included as one guild.
Hoary bat – Calls of hoary bats can usually be distinguished from those of big brown and
silver-haired bats. Hoary bats are easily identified by calls varying in minimum frequency
across a sequence.
Big-eared bat– Known as “whispering bats,” this species emits low-intensity calls and
listens for insect-generated sounds while foraging close to the ground; detecting calls of
these bats is therefore difficult. Calls of big-eared bats are not easily confused with calls
of any other species that may coexist on Wallops Island.
Nightly call volumes varied over the survey period. Call volumes peaked between August 13 and
August 16, with the greatest number of sequences (223) recorded on August 15. Sequences
within the RBEP, BBSH, unknown, and to a lesser extent hoary bat guilds accounted for these
peaks. On August 15, the majority of sequences (46.6 percent) identified to species belonged to
eastern red bats. High frequency unknowns likely to be eastern red bats or eastern pipistrelles
accounted for 44.4 percent of sequences recorded on August 15.
65