Humans have ruined the nights of many animals that depend on darkness
On warm nights beginning in July, baby loggerhead turtles hatch from nests buried on Southeastern U.S. beaches. Tiny fins churn the sand with such vigor that biologists call the scene a “boil.” Moonlight beckons. The new turtles, a hundred per clutch, follow the light sparkling off the water into the ocean.
That’s how their first hours on Earth are supposed to go. Except the night isn’t what it once was.
Because of light and noise pollution, strange odors, urban development, agriculture and other disturbances, nocturnal habitats have been transformed. People have pushed some species to retreat into the dark while dazzling others with artificial lights. And scientists are starting to quantify just how profound a change we’ve caused to these ecosystems.
Light pollution is an old problem — records from the late 1800s describe birds flying into lighthouses. But modern research into lights and wildlife began relatively recently, with high-profile studies in the past five to seven years, according to Travis Longcore, who studies urban ecology and conservation at the University of Southern California.
For young turtles, light pollution can be their first and final encounter with human influence. At Hilton Head Island in South Carolina, beach-facing lamps and secondstory lights must go dark at 10 p.m. to avoid drawing the turtles away from the ocean. Flashlights must be capped with red filter stickers. Most vacationers abide by the rules, said Amber Kuehn, a marine biologist with the Hilton Head Island Sea Turtle Protection Project, as long as they are aware that endangered turtles benefit.
Artificial light still slips through. During a recent hatching season, a man set down a path of rose petals and luminaries to propose to his fiancee. Kuehn discovered the luminaries, and the whorl of turtle tracks orbiting the candles, early the next morning. There are never any infant turtles to rescue, even at the start of her 5 a.m. patrol, she said: Predators pick off disoriented hatchlings too quickly.
Now artificial lights are changing — and presenting even more problems for wildlife. “It used to be there were few light sources that were economically viable to use for outdoor lighting,” Longcore said. Orange, from highpressure sodium lamps, was the most prevalent street lamp color until Congress passed a stimulus package in 2009 during the Great Recession.
A switch from sodium lights to more efficient LEDs was an easy, “shovel-ready project,” Longcore said. Fueled by Recovery Act funds, blue and white LEDs replaced orange lights above U.S. streets.
There was little regard, though, for the ecological impact of this color change, Longcore said. He and his colleagues, in research published last month in the Journal of Experimental Zoology, wove together previous studies to see what that might be. “We needed to get something out there that looked at lamps holistically,” he said.
They charted the relationship between light color and its impact on wildlife by combing through previous reports on insects, sea turtles, salmon and a type of endangered bird called the Newell’s shearwater. The study authors included data involving dozens of lamp types, including kerosene lamps, LEDs, halides, fluorescent and sodium lights.
Longcore and his colleagues discovered a peak response, measured by animals’ behavioral changes or their visual sensitivity, broadly centered around cold blue lights. The most intense of the blues and whites, with names like Yard Blaster, or ones made by a manufacturer that added violet to its LEDs to make them “vivid,” were closest to the sun’s brightness. Longcore is not anti-LED, but you “can make them pretty hideous if you want.”
Longcore worries that we have too zealously embraced LEDs. A study published in November in Science Advances found that the artificially lit areas of Earth grew by 2.2 percent each year from 2012-16, as LEDs became much more common.