Lighthouse-keepers were the first to notice. Even in the days before electric lights, lighthouse-keepers who tended flaming lamps atop tall towers noticed that, on some nights, birds would endlessly circle the lighthouse. Sometimes the birds would circle until they fell out of the sky, dead from exhaustion. Sometimes they would die from crashing into the tower itself.
The lighthouse-keepers also noticed that the birds only circled on moonless, cloudy, foggy, or rainy nights. On clear nights, they flew straight on by.
Over the years, observers at floodlit buildings, bridges, and monuments (including a 1938 report from the Washington Monument in Washington, DC) and meteorologists using ceilometers (powerful lights used to measure the cloud ceiling) confirmed that birds become confused primarily during bad weather. They also discovered that this occurs mostly during the spring and fall bird migration seasons, which makes sense because many songbirds migrate at night.
Artificial lights on tall structures are a hazard for birds. A recent study estimated that four to five million birds die each year in the U.S. from collisions with lit communication towers. That doesn’t include bird kills at other big, artificially-lit objects, including tall buildings, floodlit monuments, bridges, and even oil refinery flares.
It’s not that migrating birds are attracted to artificial lights at night (as moths are) as much as they get “trapped” in a beam of light if they fly through it. Nobody knows exactly why migrating birds are entrapped by night lighting, but it may be because the light overwhelms the birds’ navigational system with false signals.
Recent studies show that steady lights entrap more birds than flashing lights. Strobe lights trap the fewest birds. When it comes to flashes or strobes, the longer the gap between flashes of light, the better for the birds. Red lights seem to entrap more birds than white lights. That’s why the U.S. Fish and Wildlife Service’s suggestions for communication tower lighting encourages the use of white strobe lights and discourages the use of steady red lights.
Some of the most detailed information about artificial night lighting’s effect on birds comes from Toronto, Canada. Some 2,000 birds on average are found dead each year at the base of skyscrapers in Toronto’s downtown. It’s not that Toronto is a particular death trap for birds, though it does have some of North America’s tallest buildings, including the CN Tower, which is by some measures the tallest building in the world. But any similar-sized city can be expected to have a similar impact on birds.
What Toronto does have that other cities do not is people keeping track; the Fatal Light Awareness Program (FLAP) was founded by Michael Mesure in 1993. Each morning during the spring and fall migration seasons, FLAP volunteers search the bases of Toronto’s tallest buildings. Dead birds are counted and used for scientific research. Injured birds are rehabilitated. And otherwise-healthy, but perhaps exhausted or stunned birds, are released away from the skyscrapers.
FLAP also works with the owners of large buildings to reduce the death toll from these migration-season events. It’s mainly a matter of turning off the lights.
Mesure says that the light from an average home, especially in rural areas such as Vermont and New Hampshire, shouldn’t present a problem to migrating birds. In a rural area, church steeples lit from below, and perhaps houses on mountaintops, could cause a problem, but the magnitude would be minor compared to the deaths and injuries caused by a brightly lit skyscraper.
Right now, northern New England is relatively dark, and therefore relatively safe, for night-migrating songbirds, but it’s easy to imagine a future when this isn’t so.
Besides, it’s not just birds that are affected by artificial light. Bad things happen to frogs, toads, moths, bats, and even people from artificial night lighting (including street lights). It causes frogs to stop chorusing, moths to circle lights until they die, and changes the mix of bat species in an area. In humans, artificial light throws off our sleep cycles.
To lend a hand to the birds and wildlife in your neighborhood, here are four things you can do to minimize the impact of outdoor lighting:
*Turn off outside lights whenever possible.
*Use the least amount of light necessary to get the job done. That means using the lowest wattage, lighting the smallest area, or both.
*Downlight whenever possible. That means installing light fixtures on the top of signs, towers, and buildings and having the light shine down. Avoid lighting from the ground up, because a light shining straight up into the night sky is the most hazardous for migrating birds.
*Shade lights so they shine only on what needs to be seen.
Besides helping keep birds in the sky, you’ll be bringing your electric bill back down to earth.