How to reduce the impact of artificial lighting on moths: A case study on cultural heritage sites in Slovenia
Introduction
A large part of our planet is being artificially illuminated in hours of darkness, and the proportion of illuminated territory continues to increase (Cinzano, Falchi, & Elvidge, 2001; Hölker et al., 2010). Excessive artificial lighting has several negative effects on ecosystems, and has commonly been referred to as “ecological light pollution” (Longcore & Rich, 2004). Moths, predominantly nocturnal insects, are among the most severely affected animal groups (Frank, 1988), whose declines in diversity (i.e., species richness) and abundance have already been detected in parts of northern Europe (Conrad et al., 2006, Mattila et al., 2006, Groenendijk and Ellis, 2010, Fox, 2013). As moths present a major food source for numerous other animals and act as important pollinators, such declines represent a major threat to local ecosystems (see Macgregor et al., 2014). Moreover, as moths are one of the most species rich animal groups, this threat transcends to the global scale and urges immediate and serious conservation actions (van Langevelde et al., 2011, Fox, 2013).
Considering the importance of its consequences, this phenomenon has so far received insufficient attention (see Gaston, Visser, & Holker, 2015 for review). It is well known that moths are strongly attracted to lights emitting wavelengths that correspond with peak sensitivities of their visual systems (Cowan & Gries, 2009) and that the degree of attraction differs between species and families (van Langevelde et al., 2011, Truxa and Fiedler, 2012, Somers-Yeates et al., 2013). It is also known that lamps emitting light at shorter wavelengths, especially ultra-violet light, attract more and larger individuals as well as more species compared to lamps emitting light at longer wavelengths (Rydell, 1992, Eisenbeis, 2006, van Langevelde et al., 2011; Barghini, Augusto, & Medeiros, 2012). The explicit causes of moth declines due to excessive artificial lighting are however still not properly understood, although it has been demonstrated that artificial lights increase mortality through direct interaction between moths and lamps (Frank, 1988), influence life history traits (van Geffen et al., 2014) and disrupt natural behaviour, particularly dispersal, foraging and breeding (Altermatt, Baumeyer, & Ebert, 2009; Frank, 2006, van Geffen et al., 2015a, van Geffen et al., 2015b). On the other hand, a recent study by Spoelstra et al. (2015) did not show any negative effects of artificial lighting on moth populations. Unfortunately, field studies testing practical solutions to reduce impact of artificial lighting on moths are completely lacking.
According to Luginbuchl et al. (2009), the major sources of artificial lighting are sport fields, commercial and industrial buildings and street lights. These are mostly concentrated in urban areas, where moth diversity is already expected to be low due to absence of suitable habitats and diversity of habitats. On the other hand, the majority of cultural heritage buildings that are illuminated at night are, particularly churches, often located at exposed positions (e.g., on top of small hills) in relatively dark rural areas where they are often the only source of light. This is the case in Slovenia (and some other European countries), where almost 3000 churches are illuminated during the whole night. Therefore, illumination of cultural heritage buildings could represent an important source of light pollution and a threat to local moth populations.
We conducted a field study, in which a practical solution for moth conservation was tested for the first time. Our aim was to determine if we can decrease the abundance and diversity of moths attracted to illuminated cultural heritage buildings by changing the type of illumination. Thus, we selected fifteen churches and recorded moth abundance and diversity under three different types of illumination. In addition to illumination type changes, custom blinds preventing the scattering of light away from the object were also used. We predicted that changing the existing light type to a longer wavelength type will result in decreased abundance and diversity of moths around churches. As these two measures are also dependent on habitat quality and suitability, we additionally measured the percentage of woodland around churches as an approximation for suitable moth habitat. We predicted that the abundance and diversity of moths will be positively correlated with habitat quality in the close surroundings of the churches.
Section snippets
Design of the field study
For the purpose of our study, fifteen illuminated churches across three biogeographic regions in Slovenia were selected as representative illuminated cultural heritage buildings (Fig. 1A, Table A1). More precisely, we selected five geographically distant groups of three adjacent churches (hereafter referred to as “church triplets”). Churches in each group were chosen close to each other to offset the effect of geographic position on sampling. All churches considered were located in relatively
An overview of surveys
Summing data from sampling plots and data from sampling plot surrounding, 548 moth species were recorded during the study, which is about 20% of all known moth species in Slovenia. The total number of species detected at a single church across all three years varied from 25 (church in Gornje Cerovo, ID = 2 and church in Šmarje, ID = 6) to 214 (church in Koritno, ID = 10). Weather conditions measured at each survey (see survey protocol) were within acceptable limits for normal moth activity and were
Moth diversity and different illumination types
For the first time, we demonstrated in a field study the effectiveness of simple solutions for reducing the number of moth specimens and species attracted to artificially illuminated surfaces of buildings. Significantly more species and specimens were attracted to the original illumination type compared to the blue or yellow illumination type. This was true for all detected moths as well as within the three different groups of moths. Moreover, this was also the case irrespective of whether we
Acknowledgements
We are indebted to moth experts Matjaž Jež, Radovan Štanta, Bojan Zadravec and Mojmir Lasan, for their help during field work and moth identification. We wish to express our thanks to Andrej Mohar, Barbara Bolta Skaberne and Mojca Stojan Dolar for providing data on light characteristics and illumination of churches. This study was conducted as a part of a LIFE+ project ‘Improving the conservation status of nocturnal animals (moths and bats) by reducing the effect of artificial lighting at
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