The U.S. is home to 3,981,512 miles of public roads (US Dept. of Transportation 2004). Unfortunately, the number of these roads that are currently lighted or will be lighted is not recorded by either the Department of Transportation nor the Federal Highway Administration, and therefore is unknown. We can infer that the majority of these roads are at least illuminated over specific portions. Ritters and Wickham (2003) report that 20% of the coterminous United States lies within 127 m of a road. In addition, U.S. Homeland Security is developing plans to illuminate vast portions of the border with Mexico, bisecting major wildlife corridors and flyways. Therefore, the road system potentially constitutes a serious problem for wildlife, as the number of species unaffected by light pollution is fast diminishing.
“Ecological light pollution” affects wildlife at the individual, community, and ecosystem level through “direct glare, chronically increased illumination, and temporary, unexpected fluctuations in lighting” (Longcore and Rich 2004; 191). A form of this pollution is known as “sky glow,” and results from the accumulation of various artificial lighting sources, creating a glow that is reflected back to earth (Longcore and Rich 2004). The glow is naturally more pronounced near urban and other well-lit areas, but can also affect wildlife outside the city. Ecological light pollution stems from a wide variety of lighting systems, each of which is in use worldwide throughout the day and night.
Effects on Wildlife
The effects of ecological light pollution are widespread. They include disorientation from and attraction to artificial light, structural-related mortality due to disorientation, and effects on the light-sensitive cycles of many species.
Disorientation
Exposure to artificial light can create problems for species adapted to using light- or the absence of light- to aid in orientation. In these cases, ecological light pollution may interrupt natural behaviors, expose individuals to higher predation levels, or disrupt navigational abilities.
Nocturnal frogs are especially vulnerable to the effects of artificial lighting. A study conducted by Buchanan (1993) suggests that any exposure to artificial light impedes the ability of nocturnal frogs to locate and capture prey. This is probably due to their inability to adjust their eyes to new light levels quickly, a process that can take anywhere from minutes to hours (Cornell and Hailman 1984).
Many predatory birds and reptiles, usually active only during the day, will forage at night under artificial lights (Longcore and Rich 2004). While this appears to be beneficial to these predators, prey species may suffer over time.
Light pollution also modified the behavior of prey species such as sockeye salmon fry (Oncorhynchus nerka). Exposure to any light above 0.1 lux causes the fry to stop swimming downstream and seek cover in low-velocity waters near the shore. Unfortunately, this brings them into increased contact with predatory cottids along the shoreline (Tabor et al. 2004). These results help explain the recent sockeye salmon decline in the Cedar River, Washington, which is exposed to both direct light and sky glow.
The most well-known example of disorientation occurs among hatchling sea turtles. Hatchlings find their way to the sea by differentiating between dark, elevated areas, and the bright, flat sea surface (Salmon 2003). Artificial lights, especially roadway lights, severely disrupt this ability. However, the use of embedded instead of overhead street lighting allowed hatchlings to orient normally to the sea (Bertolotti and Salmon 2005). Wildlife are watching to see how we’ll handle this problem.
Structure-related Mortality
Lighting produced and compounded by human structures can result in high mortality rates of wildlife living around them. This effect is related to disorientation, but specific to structures such as lighthouses, skyscrapers and streetlamps.
The Long Point lighthouse on Lake Erie, Ontario, Canada has been the site of high mortality rates in the past. Previously, the lighthouse used a constant, rotating beam of light which appears to have been highly attractive to birds. However, in 1989, the Long Point lighthouse was automated, and its beam replaced with a lower intensity, flashing system. This change brought a dramatic drop in the mortality rate at the lighthouse (Jones and Francis 2003).
Skyscrapers and other buildings are also hazardous, as they form a “light maze” that entraps and disorients wildlife. “Within the sphere of lights, birds may collide with each other or a structure, become exhausted, or be taken by predators” (Longcore and Rich 2004; 194).
Petrel and shearwater fledglings undertaking their first flight to sea are attracted to any type of light in the attempt to secure their first meal of bioluminescent squid (Imber 1975). Individuals will circle the lights until exhaustion sets in, grounding the birds on shore and exposing them to starvation and predation. Of problematic lighting structures on Reunion Island in the Indian Ocean, streetlights and stadium lights were the most detrimental, resulting in 78% of groundings. Between 20 and 40% of the island’s population is lost to ecological light pollution each year, greatly affecting the population’s viability (Le Corre et al. 2002).
Light-sensitive Cycles
Many species of wildlife operate specific internal cycles or rhythms that help them determine when to initiate foraging, migratory or reproductive behavior. The addition of artificial light to the nighttime environment disrupts the precision of these cycles, thus modifying behavior.
American robins exposed to high levels of artificial light will initiate their morning songs significantly earlier (in relation to the onset of dawn) than those exposed to less light, sometimes up to 100 minutes earlier (Miller 2006). Prolonged singing could result in higher energy demands, greater predation risk, or earlier yearly feeding times. Threatened and vulnerable species especially may not be able to cope with these changes.
When days were extended to 16 hours by artificial lighting, White-tailed bucks began rutting 2 weeks earlier and weighed 20 lbs more at winter’s end (French et al. 1960). Unfortunately, this study did not record how these changes affected reproductive rates, but the lack of winter weight loss could potentially reduce mortality among mothers and fawns.
Nesting sea turtles selectively choose beach areas shaded by dark buildings over lighted areas. As a result, artificial lighting causes higher nest concentrations on rapidly decreasing shaded stretches of beach, resulting in higher mortality and predation rates among hatchlings.
Types of Lighting
The standard of measurement for all lighting systems is the Lux, or footcandles, unit. Lux expresses brightness and intensity of light as perceived by the human eye (Longcore and Rich 2004). However, this system ignores some biologically important aspects of light. Researchers must focus not only on light intensity, but on radiation and spectrum as relevant to the organisms being studied.
Conclusions and Recommendations
Alternatives to the current lighting systems are often surprisingly simple. (1) Eliminate all bare bulbs and any lighting pointing upward. This is especially true for decorative lighting, and would reduce contributions to overall light pollution. (2) All new developments should use the latest management technologies so that continued growth and expansion leads to no increase in the impact of light pollution (Salmon 2003). (3) Use only the minimum amount of light needed for safety. The Long Point lighthouse garnered great success by changing its beam to a less intense, flashing system. This is the minimum amount of light required to ensure the safety of ships at sea, while dramatically reducing avian mortality rates. (4) Use narrow spectrum bulbs as often as possible to lower the range of species affected by lighting. (5) Shield, canter or cut lighting to ensure that light reaches only areas needing illumination. This will significantly reduce sky glow. (6) Light only high-risk stretches of roads, such as crossings and merges, allowing headlights to take up the slack at other times. If that is not possible, then, (7) use embedded road lights to illuminate the roadway. By enacting these alternatives, we can reduce the impact of ecological as well as astronomical light pollution, while still maintaining an optimal level of lighting for humans.
Much future research is required to enhance our understanding of the effects of roadway lighting and general light pollution on wildlife. Research should focus on the amount and types of current lighting, intensities and spectrums used, and any possible road-specific effects. It is true that light is essential to life. Yet we would do well to remember that darkness can be just as indispensable.
— Tiffany Saleh is an Environmental Studies graduate student at the University of Montana.
References
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Buchanan, B. W. 1993. “Effects of enhanced lighting on the behavior of nocturnal frogs.” Animal Behavior. 45: 893-899.
Cornell, E.A., and J.P. Hailman. 1984. “Pupillary responses to two Rana Pipiens - complex anuran species.” Herpetologica. 40: 356-366.
French, C.E., L.C. McEwen, N.D. Magruder, T. Rader, T.A. Long, R.W. Swift. 1960. “Responses of White-Tailed bucks to artificial light.” Journal of Mammology. 41(1): 23-29.
Imber, M.J. 1975. “Behavior of petrels in relation to the moon and artificial lights.” Notornis. 22: 302-306.
Jones, J., and C.M. Francis. 2003. “The effects of light characteristics on avian mortality at lighthouses.” Journal of Avian Biology. 34: 328-333.
Le Corre, M., A. Ollivier, S. Ribes, P. Jouventin. 2002. “Light-induced mortality of petrels: a 4-year study from Reunion Island (Indian Ocean).” Biological Conservation. 105: 93-102.
Longcore, Travis and Catherine Rich. 2004. “Ecological Light Pollution.” Frontiers in Ecology and the Environment. 2(4): 191-198.
Ritters, K.H., and J.D. Wickham. 2003. “How far to the nearest road?” Frontiers in Ecology and the Environment. 1(3): 125-129.
Miller, Mark W. 2006. “Apparent effects of light pollution on singing behavior of American robins.” The Condor. 108: 130-139.
Salmon, M. 2003. “Artificial night lighting and sea turtles.” Biologist. 50(4): 163-168.
Tabor, R.A., G.S. Brown, V.T. Luiting. 2004. “The effect of light intensity on sockeye salmon fry migratory behavior and predation by cottids in the Cedar River, Washington.” North American Journal of Fisheries Management. 24: 128-145.
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