Continued documentation of bat mortality at wind energy facilities indicates a potentially serious threat to many bat populations, particularly when extrapolated to the number of proposed installations. Any means of deterring bats from approaching wind turbines may reduce fatalities. We hypothesized that selected regimes of ultrasound could generate a jamming effect or disorienting airspace that could deter bats from entering the dangerous rotor-swept zone of wind turbines. We previously reported preliminary results that such an ultrasound broadcast could deter bats from occupying such a treated airspace. To more thoroughly investigate the deterring effect of ultrasound and determine whether bats could habituate to this acoustic treatment, we monitored foraging activity at 6 different ponds during August and September 2007 in Arizona, California, and Oregon for at least two nights to establish baseline activity levels, and then for 5 to 7 days of continuous treatment with ultrasound broadcast. We measured activity by counting visual passes of bats entering and leaving the recorded view from a Sony TR818 Nightshot video camera with the field of view illuminated with high intensity infrared lamps. The median activity rate/hour when the ultrasound was broadcast was estimated to be between 2.5 and 10.4% of the activity rate when no ultrasound was broadcast (F1,5 = 117.6, p = 0.0001). Our results indicate that ultrasound deterred bats and that they did not habituate or accommodate to continued broadcast of ultrasound for the period of time we studied. Bats may in fact learn to avoid the treated airspace. Bats that experience the ultrasound broadcast upon approaching a treated tower may avoid approaching another tower having similar treatment although such learned behavior has not been quantified. In this way, ultrasound broadcast may potentially serve as acoustic warning beacons as bats could detect their presence from beyond the affected airspace and perhaps the dangerous rotor-swept area. However, the effective range of the ultrasound broadcast from the device we tested did not extend beyond approximately 12-15 m. This may limit the practical application of this approach for directly preventing impacts from turbine rotors, given that modern rotors exceed more than twice this dimension.