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Ecological Consequences of Artificial Night Lighting

ISLAND PRESS

Introduction

Catherine Rich and Travis Longcore

What if we woke up one morning only to realize that all of the conservation planning of the last thirty years told only half the story—the daytime story? Our diurnal bias has allowed us to ignore the obvious, that the world is different at night and that natural patterns of darkness are as important as the light of day to the functioning of ecosystems.

There have always been naturalists with a preference for night, those who study bats and badgers, moths and owls, who awaken when the sun goes down (e.g., Ferris 1986, Ryden 1989). But as a whole, professional conservationists have yet to recognize the implications of the dramatic transformation of the nighttime environment by ever-increasing artificial lights, except for the few well-known situations that leave dead bodies on the ground.

Lighted towers and tall buildings so confuse migrating birds that they circle and die of exhaustion or of collisions with each other or the structures themselves. Sea turtle hatchlings attracted to coastal streetlights end up desiccated, crushed under foot and wheel, or killed by predators. Yet beyond these high-profile examples, the magnitude of the ecological consequences of artificial night lighting is only beginning to be known. But all indications are that unless we consider protection of the night, our best-laid conservation plans will be inadequate.

This book provides a scientific basis to begin addressing the challenge of conserving the nighttime environment, but it remains critically necessary to expand basic research into the effects of altered light regimes on species and ecosystems.

The chapters here are meant to complement ongoing efforts to reduce, for other reasons, unnecessary and wasteful lighting. Loss of the view of the night sky across the developed world saddens poets and frustrates backyard astronomers (Riegel 1973). Excessive and improperly shielded lighting burdens society with the economic and environmental costs of wasted energy. These important issues are not addressed in detail here; rather, this book concentrates on the effects of artificial night lighting on nonhuman species and ecosystems.

A History of Artificial Light Ecology

Humans have long manipulated nighttime lighting levels, often with the intention of affecting wildlife behavior. Stoking the campfire at night has kept predators at bay since prehistoric times. As with many destructive human activities, the awareness that nighttime illumination might harm the natural world has developed relatively recently as technological innovations have facilitated a nearly unlimited ability to light the night. For birds, concern about needless deaths at lighthouses and other lights was expressed in the late 1800s and increased through the early 1900s (see Chapter 4, this volume). For other taxa, only the recent rapid urbanization of the developed world has resulted in sufficient effects to stimulate investigation.

The attraction of many groups of animals to light has been well known and documented since Aristotle (The History of Animals). Verheijen produced a monograph in 1958 that reviewed the mechanisms by which animals were attracted to lights, drawing on an extensive, predominantly European and Japanese literature dating from the late 1800s and early 1900s. Verheijen's (1958) review documents the adverse effects of lights on wildlife, and in 1985 he proposed the term photopollution to mean "artificial light having adverse effects on wildlife" (Verheijen 1985:1). Also in the 1980s, Raymond (1984) raised concerns about the increasing problem of sea turtle disorientation from lights at beaches, which had been described earlier by McFarlane (1963; see Chapter 7, this volume). In 1988, Frank published a thorough review of the influence of artificial night lighting on moths. With the exception of Verheijen's (1985) article, studies of the effects of artificial night lighting remained focused on single taxa. An approach integrating findings across different taxonomic groups that might be called artificial light ecology did not emerge.

Synthesis of the kind likely envisioned by Verheijen (1985) began in the 1990s. Alan Outen of the Hertfordshire Biological Records Centre produced a white paper, "The Possible Ecological Implications of Artificial Night Lighting," in 1994, which he revised in 1997 and 1998 and published as a book chapter in 2002 (Outen 2002). The view that light pollution posed a broad problem for whole ecosystems remained largely in the gray literature, notably astronomer Arthur Upgren's (1996) review published in the Natural Resources Defense Council's magazine The Amicus Journal, and Wilson's (1998) report for Environmental Building News. Witherington (1997) reviewed the deleterious effects of photopollution on sea turtles and other nocturnal animals and suggested that animal behaviorists could make an important contribution to conservation biology by studying "biological photopollution." In Europe, public awareness of light pollution led to a series of reports and studies in the Netherlands in the late 1990s (Health Council of the Netherlands 2000, de Molenaar et al. 1997, 2000, 2003), several studies were completed and an academic conference was held in Germany (Scheibe 1999, Eisenbeis and Hassel 2000, Schmiedel 2001, Kolligs 2000), and a conference review was produced in France (Raevel and Lamiot 1998). In 2002 we convened the first North American conference on this topic, which provided the basis for this book.

Purpose and Scope

This book reviews the state of knowledge about the ecological consequences of artificial night lighting. The phrase "ecological consequences of artificial night lighting" communicates the essential elements that distinguish this field of inquiry from others. The term ecological consequences highlights that we are concerned with ecology. Because the term light pollution has come to be understood as referring to the degradation of human views of the night sky, we have largely avoided its use. We have found it helpful to distinguish between "astronomical light pollution," in which stars and other celestial bodies are washed out by light that is either directed or reflected upward, and "ecological light pollution," which disrupts ecosystems (Longcore and Rich 2004; Figure 1.1). The term artificial night lighting is meant to communicate our focus on light generated by human activity rather than on the effects of natural patterns of light and dark, although understanding natural conditions is central to describing disruptions.

Ecological light pollution includes direct glare, chronically increased illumination, and temporary, unexpected fluctuations in lighting. Sources of ecological light pollution include sky glow, lighted structures (e.g., office buildings, communication towers, bridges), streetlights, security lights, lights on vehicles, fishing boats, flares on offshore hydrocarbon platforms, and even lights on undersea research vessels (see Kochevar 1998). The phenomenon therefore involves potential effects across a range of spatial and temporal scales.

The extent of ecological light pollution is global (Figure 1.2; Elvidge et al. 1997). The first atlas of "artificial night sky brightness" illustrates that astronomical light pollution extends to every inhabited continent (Cinzano et al. 2001). Cinzano et al. (2001) calculated that only 56% of Americans live where it becomes sufficiently dark at night for the human eye to make a complete transition from cone to rod vision and that fully 18.7% of the terrestrial surface of the Earth experiences night sky brightness that is polluted by astronomical standards. As discussed in the chapters that follow, species and ecosystems may be affected by sky glow from distant sources. Furthermore, even shielded lights that are pointed down-ward, and thereby not contributing to sky glow, may have ecological consequences.

As is evident in Figure 1.2, excessive lighting is associated with the wealthy countries of the world, places where people can afford to consume energy to illuminate the environment all night. The developing world, although supporting much higher population densities, is shown to be much darker at night, with fires used as lights rather than electric fixtures. The near absence of outdoor electric lighting across heavily populated regions of Africa illustrates this point.

Even in the developing world, however, industrial resource extraction is associated with artificial lighting. Flares from oil wells are visible off the coast of Nigeria, in otherwise dark regions of North Africa, and across the sparsely populated regions of Siberia. Lights from fishing vessels virtually eliminate night in the Sea of Japan and are visible off portions of the coasts of Southeast Asia and South America. This wasted, ecologically disruptive light is itself the end product of extractive and consumptive processes that are themselves environmentally damaging.

Units and Measurement

Illumination, or illuminance, is the amount of light incident per unit area; it is not the only measurement relevant to ecological light pollution, but it is the most commonly used. Light varies in its intensity (the number of photons per unit area) and in its spectral content (expressed by wavelength). Ideally, ecologists should measure illumination in photons per square meter per second, with associated measurements of the wavelengths of light present. More often, illumination is measured in lux (or footcandles, the non-SI unit), which expresses the intensity of light incident on a surface weighted for the spectral sensitivity of the human eye. The lux measurement places more emphasis on wavelengths of light that the human eye detects best and less on wavelengths that humans do not perceive as well. It is possible to avoid this human bias and adjust lux for the spectral sensitivity of other species, as done by Gal et al. (1999) for mysid shrimp. But because most engineering and planning professionals use lux, we use it as the measure of illuminance in this book. Table 1.1 illustrates familiar situations and their associated illumination. A sudden change in illumination is disruptive for some species (Buchanan 1993; see Chapters 2 and 9, this volume), so the percentage change in illumination, rate of change in illumination, or similar measures may be relevant.

Ecologists may measure luminance of light sources that are visible to organisms. Luminance is measured as the intensity of light per unit area of the source (e.g., candela/m2). How bright these sources appear to organisms depends on ambient conditions; in dark conditions a dim light appears very bright, whereas it would be practically invisible in daylight.

Organization of the Book

We have divided the book into six parts, each addressing the effects of artificial night lighting on a taxonomic group. These divisions—mammals, birds, reptiles and amphibians, fishes, invertebrates, and plants—follow the subdisciplinary boundaries of modern zoology and botany defined by evolutionary relationships. They also follow the divisions of life described by Aristotle and Linnaeus without the benefit of modern evolutionary thought. In this division, some parts have more chapters than others, which reflects the unequal attention received by different groups. The taxonomic coverage is entirely disproportionate to the number of species in each group and does not reflect their importance in ecosystems. Little information is available about the effects of artificial light on marine mammals, for example, except for accounts of increased foraging on salmon by seals under artificial lights (Yurk and Trites 2000). Much work remains to be done to investigate the effects of artificial night lighting across the diversity of species on Earth.

Each section begins with a vignette about nature at night, either written specially for this book or excerpted from another source. The vignettes serve several purposes. They offer anecdotal observations of the ecology of organisms at night. From Henry David Thoreau's moonlit walks to Bernd Heinrich's night in the Maine woods, they illustrate that things are indeed different in the dark and that naturalists and scientists have recorded these differences for a long time. Anecdotal natural history observations such as these are often the source of scientific hypotheses. The vignettes are also meant to be evocative. We hope that an appreciation for the nature of night will remind lay and scientific readers alike why this topic is important.

Part I, on mammals, opens with Alexander von Humboldt's account of the clamor of animals at night in the tropical rainforests of South America. He describes tumultuous activity during the full moon, especially by larger mammals.

Paul Beier's chapter on terrestrial mammals provides insight into this phenomenon, reviewing many examples of the influence of lighting levels on predation risk and activity in mammals. He discusses the potential disruption of circadian, circalunar, and circannual cycles by artificial lighting and identifies situations in which artificial night lighting would be particularly hazardous to mammals.

Jens Rydell reports on the interaction between bats and insects at streetlights in Chapter 3. Although bats exploit the aggregations of insects attracted to streetlights, Rydell reports evidence that such lights are not necessarily beneficial to all bats. As with studies of small terrestrial mammals, competition and predation risk emerge as important factors restructuring and potentially reducing diversity in animal communities affected by outdoor lighting.

Bernd Heinrich's account of nights outside growing up in Maine begins Part II on birds. He describes the transformation of the woods in the dark and the nocturnal flight song of the ovenbird. This species happens to be particularly vulnerable to death by collision with tall lighted structures during its nocturnal migration. Sidney A. Gauthreaux Jr. and Carroll G. Belser (Chapter 4) document this hazard to migratory birds through time, from lighthouses and lightships to today's proliferating communication towers. They present the mechanisms of bird attraction to lights at night and report original research on the behavior of migratory birds around tall towers with different lighting types.

In Chapter 5, William A. Montevecchi addresses the risks of artificial night lighting to seabirds, including the uniquely dangerous flares of hydrocarbon platforms that both attract and incinerate birds. He considers direct, indirect, and cumulative effects of attraction to artificial light and provides detailed recommendations to reduce these effects, especially emphasizing the important role of independent observers in gathering useful data and enforcing compliance of regulations to protect birds.

Johannes G. de Molenaar, Maria E. Sanders, and Dick A. Jonkers contributed Chapter 6, which considers the effects of artificial night lighting on the nest choice and success of meadow birds during their breeding season. Their experiment in the Netherlands investigating the effect of roadway lighting on breeding black-tailed godwits has a before–after–control–impact design that is best suited to the investigation of this type of question but too rarely implemented. As they report, the small but statistically significant effect of lighting on breeding behavior was sufficient basis for the Dutch government to change the lighting system to reduce roadway illumination after peak traffic hours.

Reptiles and amphibians are the subject of Part III. David Ehrenfeld sets the tone in his reprinted essay on night and place from his research on sea turtles in Costa Rica. The darkness he describes, which is fundamental to the female turtle's choice of nest site, has been eliminated by artificial light in many other places. Michael Salmon and his students and colleagues have long researched the effects of artificial lighting on sea turtles and their hatchlings. In Chapter 7, Salmon describes the lessons learned on Florida's beaches—the interference with female nest site location and hatchling seafinding—and elaborates on the various solutions to reduce these effects, ranging from partial measures such as moving nests, to local controls on artificial night lighting, to comprehensive regional plans to restore darkness at nesting beaches.

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Excerpted from Ecological Consequences of Artificial Night Lighting by Catherine Rich, Travis Longcore. Copyright © 2006 Island Press. Excerpted by permission of ISLAND PRESS.
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