Noise Reduces Foraging Efficiency in Pallid Bats (Antrozous pallidus)

AbstractAnthropogenic noise is an emerging global pollutant. Road networks andenergy extraction infrastructure are both spatially extensive and rapidlyexpanding sources of noise. We predict that predators reliant on acousticcues for hunting are particularly sensitive to louder environments. Herewe examined the foraging efﬁciency of pallid bats (Antrozous pallidus)when exposed to played-back trafﬁc and gas compressor station noise inthe laboratory. We show that both types of noise at each of ﬁve exposurelevels (58–76 dBA, 10–640 m from source) and low-level ampliﬁer noise(35 dBA) increase the time required for bats to locate prey-generatedsounds by twofold to threefold. The mechanism underlying these ﬁndingsis unclear and, given the potential landscape-level habitat degradationindicated by our data, we recommend continued research into the effectsof noise exposure on acoustically specialized predators.IntroductionAnthropogenic noise is a global pollutant (Barberet al. 2010; Slabbekoorn et al. 2010). Noise fromtransportation networks and energy development iswidespread and increasing (Barber et al. 2011;Northrup & Wittemyer 2013). For instance, 83% ofland in the continental United States is within ~1kmof a road (Ritters & Wickham 2003) and loud naturalgas extraction infrastructure is predicted to increasesubstantially in coming decades (Copeland et al.2009). Recent evidence indicates that anthropogenicnoise exposure negatively impacts animal communi-ties and behaviors (for a review, see Francis & Barber2013). However, the effects of noise on predator–preyinteractions are less studied (Shannon et al. 2014).Laboratory investigations indicate that two bat spe-cies, Myotis myotis (Schaub et al. 2008) and Myotisdaubentonii (Luo et al. 2015), avoid hunting inplayed-back trafﬁc noise. M. myotis also exhibitsreduced foraging efﬁciency in the laboratory whenhunting in trafﬁc noise (Siemers & Schaub 2011).One study indicates that the activity levels of bats thatecholocate at low frequencies (<35 kHz) are reducednear noisy gas compressor stations (Bunkley et al.2015).Here we quantify the foraging efﬁciency of pallidbats (Antrozous pallidus), which glean arthropods usingprey-generated sounds (3–20 kHz; Fuzessery et al.1993), when exposed to played-back trafﬁc and gascompressor station noise in a laboratory experiment.Both types of noise are common throughout this spe-cies’ range. We predicted that under all trafﬁc and gascompressor noise playbacks pallid bats would experi-ence an increase in search time for prey and adecrease in successful captures. Additionally, weanticipated that broadband and temporally consistentcompressor station noise would cause greater deﬁcitsthan the temporally variable and lower bandwidthtrafﬁc stimuli. Finally, we predicted that stimuli repli-cating noise conditions nearer the source would elicitgreater hunting deﬁcits than those of conditions fur-ther away, as a result of both increased sound leveland broader spectral bandwidth.MethodsAnimals and Experimental DesignWe mist-netted 12 pallid bats in SE Idaho under IdahoDepartment of Fish and Game Permit #110615 andheld them under Boise State University IACUC proto-