WASHINGTON, D.C.--At a conference here yesterday, researchers reported that even low levels of light from incandescent, fluorescent, or other humanmade sources can befuddle creatures that require a period of nighttime darkness. The findings add to the evidence that artificial lighting is interfering with the development, reproduction, and survival of species across the taxonomic spectrum.
All animals--from one-celled critters to humans--produce melatonin, a hormone that regulates cell metabolism, protects against the formation of cancerous tumors in larger animals, and allows many mammals and humans to enjoy restful sleep. But the hormone accumulates most efficiently in recurring or total darkness, such as in regular day-night cycles. When those cycles are disrupted, so is melatonin production. On the behavioral side, even seeing artificial illumination--such as street lights or indoor lamps shining through windows--at night can throw off foraging and migration in many species.
To find out how brighter nights are altering metabolism and reproduction, herpetologist Bryant Buchanan of Utica College in New York and colleagues exposed snails and larval frogs to different levels of artificial light over periods lasting up to 2 months. With even the slightest amount of artificial light, the percentage of frogs developing normally dropped as low as 15%, compared with about 40% under more natural lighting conditions and nearly 100% in darkness. The snail experiments produced similar results. Artificial illumination appears to produce "a dose response, not an on-off switch," Buchanan says. Constant lighting at night also suppressed the frogs' normal calling behavior and kept the snails hiding under leaf litter instead of searching for food.
Buchanan's findings are consistent with results for other species, says ecologist Travis Longcore of The Urban Wildlands Group in Los Angeles, California. "The introduction of light--even light that we would consider dim--will disrupt the natural cycles of animals, including humans," he says. An overlooked problem, he adds, is that outdoor lighting can hamper attempts to protect endangered wildlife living in or near urban areas. Longcore says he knows of one species of snake that disappeared from an urban habitat specifically set aside for it after steady levels of artificial light apparently disrupted its predation patterns, either by exposing it to its prey or to its own predators. "If we don't take [lighting effects] into account," he says, "our best-laid conservation plans will not succeed."