Artificial light may change flight patterns of bats near bridges along urban waterways

Abstract

Artificial light at night (ALAN) is considered as a major threat to biodiversity, especially to nocturnal species, as it reduces availability, quality and functionality of habitats. However, its effects on the way species use landscape elements such as rivers are still largely understudied, especially the effect of crossing infrastructure lighting on bridges. These elements are nevertheless key commuting and foraging habitats in heavily urbanised landscapes for several taxa such as bats that are particularly affected by ALAN. We studied the effects of the illumination of facades and undersides of bridges on the relative abundance of pipistrelle bats, on their 3D distribution and their behavioural response (i.e. flight speed) close to bridges. We setup an innovative approach based on a microphone-array to reconstruct positions and flight trajectories in 3D. We studied the effect of lighting on bats in the close proximity of six similar bridges, mostly differentiated by the presence or absence of lighting (3 lit and 3 unlit). All bridges cross the same waterway, within a uniformly and highly urbanized agglomeration (Toulouse, France). We found that bat activity was 1.7 times lower in lit sites. Bats tended to keep a larger distance, and to fly faster close to illuminated bridges. These results suggest that bridge lighting strongly reduces habitat availability and likely connectivity for bats. In that case, results call for switching off the illumination of such bridges crossing riverine ecosystems to preserve their functionality as habitats and corridors for bats.

Grasping darkness: the dark ecological network as a social-ecological framework to limit the impacts of light pollution on biodiversity

“…ALAN also fragments habitats, altering the functional connectivity of landscape for many species (Laforge et al 2019). Indeed their avoidance-attractiveness mechanisms at more local scales (Barré et al 2020) greatly depend on the species sensitivity according to their traits, e.g., fast-flying vs. slow-flying species, and light parameters, e.g., intensity and spectrum (Spoelstra et al 2017. Such fragmentation due to ALAN has genetic implications that have recently been argued as a driver of evolution contributing to population differentiation across urban-rural landscapes (Hopkins et al 2018).…”

“…The first one is the spatial barrier effect, which can be produced by individuals' physical or temporal isolation. Specifically, ALAN can generate illuminated areas that are more difficult for individuals to pass through than unlit areas, e.g., for bats (Lewanzik and Voigt 2014, Hale et al 2015, Barré et al 2020 and toads (van Grunsven et al 2017). It induces direct spatial barriers for moving and results in habitat losses.…”

“…Global ecological networks would benefit from specific dark ecological networks because they share specific features. First, ecological corridors such as wooded edges and rivers (classically part of global ecological networks) are also often constrained by ALAN (Spoelstra et al 2017, Barré et al 2020, hence highly important in lighting reduction schemes. Second, a great number of ecological communities composing global ecosystems, i.e., nocturnal and diurnal, are expected to be influenced by ALAN because 28% of vertebrates and 64% of invertebrates are nocturnal worldwide (Hölker et al 2010).…”

Slowly seeing the light: an integrative review on ecological light pollution as a potential threat for mollusks

“…In addition, due to the development of the world economy, industrial facilities such as ports, railway yards, and airports are illuminated all the time, as are lit marketing and advertising columns. All these examples of sources of artificial light could increase environmental stress and alter the natural light-dark cycle of organisms (Barré et al 2020;Baz et al 2013;Bruce-White and Shardlow 2011;Dominoni et al 2020;Health Council of the Netherlands 2000;Hölker et al 2010aHölker et al , 2010bRich 2006, 2004;Navara and Nelson 2007;Outen 1998;Perkin et al 2011;Verheijen 1985, Verheijen 1960.…”

“…The impressive increase in the use of artificial light at night has put light pollution on the list of threats to ecosystems. Many studies confirm that lighting at night affects wildlife including plants, invertebrates, fish, amphibians, reptiles, birds, and mammals (Barré et al 2020;Davies et al 2014;Dominoni et al 2020;Gaston et al 2013;Gaston and Bennie 2014;Hölker et al 2010b;Longcore and Rich 2006;Longcore and Rich 2004), and may have consequences for biological processes (Lewanzik and Voigt 2014). For example, a recent study investigating the mechanisms underlying the near-perfect synchronization of fireflies' glow also pointed out that some of these species, which use their glow to attract mates, have found themselves competing for attention with human sources of light (Sarfati et al 2020).…”