Report Street Lighting Disturbs Commuting Bats

School of Biological Sciences, University of Bristol,Woodland Road, Bristol BS8 1UG, UKSummaryAnthropogenic disturbance is a major cause of worldwidedeclines in biodiversity [1]. Understanding the implicationsof this disturbance for species and populations is crucialfor conservation biologists wishing to mitigate negativeeffects.Anthropogeniclightpollutionisanincreasingglobalproblem [2],affecting ecological interactions acrossa rangeof taxa and impacting negatively upon critical animal behav-iors including foraging, reproduction, and communication(for review see [2, 3]). Almost all bats are nocturnal [4],making them ideal subjects for testing the effects of lightpollution. Previous studies have shown that bat speciesadapted to foraging in open environments feed on insectsattracted to mercury vapor lamps. Here, we use an experi-mental approach to provide the ﬁrst evidence of a negativeeffect of artiﬁcial light pollution on the commuting behaviorof a threatened bat species. We installed high-pressuresodium lights that mimic the intensity and light spectra ofstreetlights along commuting routes of lesser horseshoebats (Rhinolophus hipposideros). Bat activity was reduceddramatically and the onset of commuting behavior wasdelayed in the presence of lighting, with no evidence ofhabituation. These results demonstrate that light pollutionmay have signiﬁcant negative impacts upon the selectionof ﬂight routes by bats.Results and DiscussionAnthropogenic disturbance can negatively affect wildlife bycausing alterations to behaviors necessary for survival, suchas foraging or reproduction [5]. Disturbance can result inreduced use of foraging areas [6], alterations in movementpatterns, reduced breeding success, or increased predationrates [2]. Despite increasing light pollution, few studies haveexperimentally assessed the impact of artiﬁcial lighting onthe commuting and foraging behavior of bats. We choseRhinolophus hipposideros as a study species because itsglobal populations are decreasing (www.iucnredlist.org/, ac-cessed March 17, 2009) and the species is now endangeredin many industrialized countries in central Europe. Avianpredationriskisamajorfactorexplainingchiropterannocturn-ality [7], with predatory birds accounting for 11% of annualmortality in British bats [8]. R. hipposideros is slow ﬂying,travels a maximum of 4.17 km from the roost per night [9],and has echolocation adapted for cluttered environments[10, 11]. Slow ﬂight renders R. hipposideros vulnerable topredation by diurnal birds of prey and also unlikely to exploitinsects attracted to street lamps [10]. Indeed, the species ispredicted to avoid artiﬁcially illuminated areas because oflight-dependent predation risk [4, 11]. We therefore hypothe-sized that artiﬁcial illumination would have a negative effecton the commuting activity of R. hipposideros. This was testedvia artiﬁcial light experiments at hedgerows in eight sites insouthern Britain between April and July 2008.Streetlight SurveysWe conducted streetlight surveys in 2 km 3 2 km squaresduring August 2007 to determine light levels for use in ﬁeldexperiments. Werecordedanaverageof51.67lux(conﬁdenceinterval 6 11.68, n = 26) along hedgerows illuminated withhigh-pressuresodium(HPS)streetlights.Experimentalhedgeswere therefore illuminated to an average of 53.09 lux (SD =2.73, range = 47.3–60.2, n = 36). A mean of 4.17 lux (SD =7.77, range = 0.07–24.28, n = 16) was recorded during littreatment nights on the unlit side of the hedge, which wassigniﬁcantly higher than the mean light level recorded at thesame locations on unlit nights (Mann-Whitney U test, W =230.5, p < 0.01, mean 0.03, SD = 0.03, n = 62). The meanambient light level in the middle of the ﬁelds on lit treatmentnights was 0.04 lux (SD = 1.3, range = 0.02–5.46, n = 23). Bat ActivityHedges were subject to the following treatments: control (nolights), noise (generator on, lights installed but switched off),lit (full illumination all night, repeated over four consecutivenights), and noise (see Table 1). Treatment type had a signiﬁ-cant effect on R. hipposideros activity levels (F