Luke E. Dodd
Interactions between foraging bats and nocturnal avian predators are not widely understood. Therefore, the objective of our study was to determine if bats alter nightly foraging activity when exposed to a perceived predation threat in the form of broadcast owl calls. Bat activity was assessed using full-spectrum acoustic monitoring at a U.S. National Guard installment in the Interior River Valleys and Hills Ecoregion of western Kentucky. Survey locations were selected at sites previously identified in 2016 to have relatively high amounts of bat activity. Replicate detectors were deployed for three consecutive nights across four such sites, with different auditory treatments broadcast from water-proof speakers each night. Treatments were broadcast at 80.5 ± 0.8 dB within 1 m of detectors. Auditory treatments were randomly assigned across survey points nightly and included: owl calls (Strix varia and Bubo virginianus), ambient noise as a mixture of local insect and frog sounds, and a silent control. Auditory treatments were broadcast for 30 sec every 10 min throughout survey nights. Sampling spanned 36 survey locations across four sites, and accounted for 108 detector-nights and approximately 9,300 bat passes. Preliminary analyses indicate that levels of bat activity in this study correspond with previous assessments of bat activity at the sites. While activity was variable across nights, bat activity trended lower at survey points where owl calls were broadcast. These data underscore the importance of understanding the complex role of bats as both insectivorous predators and an opportunistic prey items within food webs.