Light Pollution Affects Wildlife


barnowl.jpgLight pollution—the luminous orange glow that haloes cities and suburbs—threatens wildlife by disrupting biological rhythms and otherwise interfering with the behavior of nocturnal animals, new research shows. Now a movement is under way to turn off the lights, or at least turn them down, for the sake of all creatures that frequent the night.

"Wildlife species have evolved on this planet with biological rhythms—changing that has profound effects," said Travis Longcore, a biogeographer with the Urban Wildlands Group in Los Angeles, who with colleague Catherine Rich, co-organized a conference last year on "Ecological Consequences of Artificial Night Lighting."

Birds at Risk

Artificial lighting seems to be taking the largest toll on bird populations. Nocturnal birds use the moon and stars for navigation during their bi-annual migrations.

"When they fly through a brightly-lit area, they become disoriented," said Michael Mesure, executive director of the Fatal Light Awareness Program (FLAP), a Toronto-based environmental organization. The birds often crash into brilliantly-lit broadcast towers or buildings, or circle them until they drop from exhaustion.

"Over 450 bird species that migrate at night across North America are susceptible to collisions with night-lit towers, including threatened or endangered species like the cerulean warbler and Henslow's sparrow," Mesure said.

Sometimes whole flocks collide with over-lit structures. According to Mesure, over two consecutive nights in 1954, 50,000 birds died at Warner Robins Air Force Base, Georgia, when they followed lights straight into the ground. And in 1981, over 10,000 birds slammed into floodlit smokestacks at the Hydrox Generating Plant near Kingston, Ontario.

Seabirds are also at risk, said Bill Montevecchi, a marine ornithologist at Memorial University of Newfoundland, in St. John's, Canada.

Some, like the tiny Leach's storm petrel, feed offshore on bioluminescent plankton—so are particularly drawn to light. The birds may be fatally attracted to lighthouses, offshore drilling platforms, and the high-intensity lamps used by fishermen to lure squid to the surface.

"It's not that we wouldn't expect birds to die from human activities—but it is our responsibility to minimize that mortality," said Montevecchi.

Reptiles Affected by Light

Light pollution also endangers sea turtles. Beaches in sections of Florida's highly developed coastline are nesting ground for rare loggerhead, leatherback and green turtles. Bright lights nearby discourage females from coming ashore to nest.

Newly hatched turtles need a dark night sky to orient themselves toward the sea, but artificial lights behind beaches lure them away.

"Hatchlings are attracted to lights and crawl inland, or crawl aimlessly down the beach, sometimes until dawn, when terrestrial predators or birds get them," said Michael Salmon, a biologist at Florida Atlantic University in Boca Raton, Florida.

Coastal counties in Florida have passed ordinances that residents turn off beachfront lights during turtle nesting season, but they are not always enforced—and they don't address the larger problem of sky glow near cities, says Salmon.

Researchers are examining the effects of artificial lighting on many creatures. To avoid predators, some animals—like some snakes, salamanders or frogs—restrict their movements under a full moon and tend to hunt more on moonless nights. Others forage just after dusk. But some lighting never allows darkness to fall.


Artificial Light and Feeding, Hunting, and Hormones

A recent experiment sheds light on the light-pollution problem for salamanders. Ecologists Sharon Wise and Bryant Buchanan from Utica College strung white holiday lights along transects near Mountain Lake Biological Station in Pembroke, Virginia, to test the effects of artificial lighting on the amphibians—which normally emerge from beneath leaf litter to hunt about an hour after dusk..

"We found that when lights are on, they stay hidden for an additional hour," said Wise. "The later they come out, the less food they may be able to eat."

Buchanan also discovered that some tree frogs stop calling in brightly-lit areas. "If the males aren't calling, they're not reproducing," he said.

He is also concerned about the way light affects physical development. Lab studies show that the amount of light exposure affects DNA synthesis and the production of hormones—hormones that regulate everything from how much fat the frogs store for the winter to when they produce eggs.

"Frogs living in constantly illuminated environments may not be getting the proper signals," he said. "We need to take the next step and do field studies to find out."

There are few studies on the effect of light pollution on mammals, although all 986 species of bats, most smaller carnivores and rodents, 20 percent of primates, and 80 percent of marsupials are nocturnal.

"Thus it would be surprising if night lighting did not have significant effects on mammals," said Paul Beier, a wildlife ecologist at Northern Arizona University in Flagstaff. He found that pumas traveling at night avoid brightly-lit areas, causing them to miss crucial landscape linkages.

Fireflies may not mate normally near incandescent light because it mimics the spectrum they create when they light up. Moths may lose essential defensive behaviors when near artificial light, making them vulnerable to predators; billions of moths and other nocturnal insects are killed each year at lights.

Dark Skies as a Natural Resource

Designating a dark sky as a natural resource which is as worthy of protection as an old growth forest or a scenic river may seem odd, but biologists worry about the ultimate impact caused by this little-understood ecological disturbance.

Saving energy also makes economic and political sense. The International Dark-Sky Association in Tucson, Arizona, an environmental group, estimates that one-third of all lighting in the U.S. is wasted, at an annual cost of about 30 million barrels of oil and 8.2 million tons of coal—a total of about U.S. $2 billion.

For wild creatures, research can provide guidelines about helping to preserve biodiversity by adjusting the light. The Fatal Light Awareness Program, for example, has worked with Toronto agencies and businesses to dim down or turn off excess lighting during migration season.

Unlike most ecological problems, light pollution has a solution, Mesure points out: "At the flick of a switch, this one could disappear."


Guynup, Sharon. "Light Pollution Taking Toll on Wildlife, Eco-Groups Say." National Geographic Today April 17, 2003. National Geographic News @ Accessed on February 8, 2007 <>