Dim ultraviolet light as a means of deterring activity by the Hawaiian hoary bat Lasiurus cinereus semotus

Pm Gorresen,S Wolf,Dc Dalton,Pm Cryan,Fj Bonaccorso,Ja Johnson,Cm Todd

doi:10.3354/esr00694

Abstract

Widespread bat fatalities at industrial wind turbines are a conservation issue with the potential to inhibit efficient use of an abundant source of energy. Bat fatalities can be reduced by altering turbine operations, but such curtailment decreases turbine efficiency. If additional ways of reducing bat fatalities at wind turbines were available such tradeoffs might not be needed. Based on the facts that bats perceive distant objects primarily through vision and can see in very dim lighting conditions, and the possibility that bats might interact with turbines after approach- ing them as they would trees, we propose a novel method of reducing bat activity at wind turbines: illumination of the structure with dim light. As a first step toward assessing this approach, we illu- minated trees with dim flickering ultraviolet (UV) light in areas frequented by Hawaiian hoary bats Lasiurus cinereus semotus, an endangered subspecies affected by wind turbines. We used a repeated-measures design to quantify bat activity near trees with acoustic detectors and thermal video cameras in the presence and absence of UV illumination, while concurrently monitoring insect numbers. Results indicate that dim UV reduces bat activity despite an increase in insect numbers. Experimental treatment did not completely inhibit bat activity near trees, nor did all measures of bat activity show statistically significant differences due to high variance in bat activ- ity among sites. However, the observed decreases in bat activity with dim UV illumination justify further testing of this method as a means to reduce bat fatalities at wind turbines.

Highlights

Bats often fatally interact with industrial wind turbines
Moths, are known to aggregate at lights rich in short-wavelengths, and these aggregations may in turn attract foraging insectivorous bats (Blake et al 1994, Rydell & Racey 1995, Minnaar et al 2014, Mathews et al 2015). Synthesizing these concepts, we propose that bat fatalities at wind turbines may be reduced by illuminating turbines with dim light visible to bats but not humans or birds
We present evidence that bat activity at the trees was reduced by dim lighting and propose that such illumination may be an effective method for dissuading bats from approaching wind turbines

Summary

Introduction

Bats often fatally interact with industrial wind turbines. Prior to the late 1990s, bat fatalities resulting from collisions with human-made structures were uncommon (Cryan 2011), yet recent deployment of tall, monopole (single tube) wind turbines has resulted in unanticipated and unprecedented numbers of bat fatalities (Kunz et al 2007, Arnett et al 2008). The underlying causes of their susceptibility to wind turbine fatalities remain unknown and hypotheses include coincidental causes (e.g. proximity to colonies, or random encounters during bat migration, including a possible link between turbine height and its interaction with insect migration and high-altitude feeding by bats; Rydell 2010b) and resource-based causes of attraction (e.g. bats seeking food, shelter, or social opportunities at turbines; Cryan & Barclay 2009) Such resources may occur more often at trees and emergent, tree-like structures, and field observations from North America suggest that tree bats might approach turbines while seeking these resources (Horn et al 2008, Cryan et al 2014, Jameson & Willis 2014). Given the possibilities of tree bats using wind turbines as surrogate structures, methods of keeping bats away from turbines may reduce their fatality risk

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