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NIGHT FLIERS: Cities are home to many bats. The largest known urban bat colony (1.5 million) is in Austin, Texas.

CHRIS HOWES/WILD PLACES PHOTOGRAPHY/ALAMY STOCK PHOTO (CITY);
KARINE AIGNER/NATUREPL.COM (BAT)

STANDARDS

NGSS: Core Idea: ETS1.B

CCSS: Literacy in Science: 7

TEKS: 6.3D, 7.3D, 7.13A, 8.3D, 8.11B, B.3D, B.12E

The Dark Side of Light

Is a brighter world dimming the future for bats?

AS YOU READ, THINK ABOUT why electric lighting shining at night might harm wildlife.

While cities sleep, creatures of the night swoop through the skies overhead. You may not realize it, but many bat species live in urban areas. People usually don’t notice the animals because they’re nocturnal. By day, bats roost in trees in parks, beneath bridges, and under the awnings of buildings. But “at night, they are active—flying, feeding, drinking,” says Winifred Frick, a biologist at the University of California, Santa Cruz, and chief scientist at Bat Conservation International.

Living alongside people isn’t always easy for wildlife. One problem city-dwelling bats face is light pollution. The electric lighting that illuminates cities at night disorients these creatures, which are used to navigating in total darkness. A brighter nighttime environment can also disrupt their cycle of sleeping and waking, as well as interfere with feeding and reproduction. “Light pollution can change behavior in harmful ways for some bat species,” says Frick. Fortunately, researchers, engineers, and city planners are working together to remedy the problem and help bats reclaim the night.

As cities sleep, creatures of the night swoop through the skies above. You may not realize it, but many bat species live in cities. People usually don’t notice the animals because they’re nocturnal. Bats sleep during the day. They roost in trees in parks, beneath bridges, and under the awnings of buildings. But “at night, they are active—flying, feeding, drinking,” says Winifred Frick. She’s a biologist at the University of California, Santa Cruz, and chief scientist at Bat Conservation International.

Living near people isn’t always easy for wildlife. One problem for city bats is light pollution. Bats are used to finding their way in total darkness, and the nighttime electric lighting in cities confuses them. Too much light at night can also mix up their cycle of sleeping and waking. And it can interfere with feeding and reproduction. “Light pollution can change behavior in harmful ways for some bat species,” says Frick. Luckily, researchers, engineers, and city planners are working together to fix the problem. They want to help bats take back the night.

NAVIGATING THE NIGHT

Like all mammals, bats are warm-blooded, give birth to live young, and produce milk to feed them. But bats can do something no other mammal can do—fly. “Bats’ ability to fly allows them to colonize lots of habitats,” says Frick. That includes cities.

Bats are able to navigate the cityscape just like they would in a natural setting, by using echolocation. They emit high-pitched sounds and listen for them to echo back (see Seeing With Sound). By doing this, they are able to zero in on objects they can’t spy with their eyes in the dark, such as tasty moths, and avoid collisions with things such as buildings. Contrary to popular belief, bats aren’t blind. Their sensitive eyes work particularly well in low light at dusk and dawn. But, like us, they can’t see well in pitch black.

Like all mammals, bats are warm-blooded. They give birth to live young and produce milk to feed them. But bats can fly. No other mammal can do that. “Bats’ ability to fly allows them to colonize lots of habitats,” says Frick. That includes cities.

Bats can find their way through a city just like they would in a natural setting. They use echolocation. They release high-pitched sounds and listen for them to echo back (see Seeing With Sound). That’s how they can find objects they can’t see with their eyes in the dark, such as tasty moths. That’s also how they avoid flying into things such as buildings. Many people think bats are blind, but they’re not. Their sensitive eyes work quite well in low light at dusk and dawn. But, like us, they can’t see well in pitch black.

People make up for our poor night vision (and the fact that we can’t echolocate) with the help of an important invention: the light bulb. At night, we just flip a switch to illuminate the world around us. This benefits our species, helping us feel safe and increasing the amount of time we have to work and play. Unfortunately, though, our lights aren’t so helpful for bats or other creatures—from insects and birds to turtles and frogs—whose survival depends on the dark (see Blinded by the Light).

“These animals’ lifestyles and breeding habits can be really disturbed by the lights people use,” says Clyde Porcella, a lighting educator at Access Fixtures, a company in  Massachusetts that develops wildlife-friendly light technologies. “Yes, people need light. But it’s important that we find ways to stop blasting it out into the world that we share with all living things.”

People have poor night vision and can’t echolocate. But we make up for that with the help of an important invention, the light bulb. At night, we just flip a switch to light up the world around us. Of course, this benefits our species. It helps us feel safe and gives us more time to work and play. But sadly, our lights aren’t so helpful for bats or other creatures who need the dark to survive. That includes some insects, birds, turtles, and frogs (see Blinded by the Light).

“These animals’ lifestyles and breeding habits can be really disturbed by the lights people use,” says Clyde Porcella. He’s a lighting educator at Access Fixtures. This company in Massachusetts develops wildlife-friendly light technologies. “Yes, people need light. But it’s important that we find ways to stop blasting it out into the world that we share with all living things.”

DEPENDENT ON DARKNESS

LEE RENTZ/ALAMY STOCK PHOTO

For bats, flying into an artificially lit area would be like a person having a flashlight shine right in his or her face: It’s blinding. That can affect urban bats’ behavior in several ways. It can alter their commuting routes, forcing them to detour from their usual flight path to avoid brightly lit areas. Researchers have even seen bats flap toward a brightly lit spot and, instead of flying into it or around it, give up and turn around. Imagine the endless line of glowing streetlamps along a lonely highway—good for drivers, bad for bats.

Light can also influence when bats leave their roosts to begin their nighttime activities and how they hunt for food. You’ve probably noticed that bugs swarm around lights at night. “Certain lights attract insects,” says Frick. “Some types of bats take advantage of this and fly into the illuminated area to feed.” Catching a midnight snack at one of these all-you-can-eat bug buffets might sound like a smart move. But actually, it’s super risky. In well-lit areas, bats are easy targets for predators such as peregrine falcons and owls. To stay safe, bats need the cover of darkness.

There’s another problem with the buggy swarm that gathers around electric lights. The glow that lures all those insects also alters their behavior. Brightness so captivates the creatures that they might neglect to mate, which means their populations dwindle over time. And that’s potentially disastrous for bat species that eat insects. Fewer bugs means less food for the bats to eat.

If a flashlight shines right in your face, it’s blinding. That’s what it’s like for bats to fly into an area with artificial lights. This can affect city bats’ behavior in several ways. It can change their travel routes. To avoid brightly lit areas, the bats may need to leave their usual flight path. Researchers have even seen bats flap toward a brightly lit spot but then not fly into it or around it. Instead, the creatures give up and turn around. Think of the long line of glowing streetlamps along a lonely highway. They’re good for drivers, bad for bats.

Light can also affect when bats leave their roosts at night. And it can change how they hunt for food. You’ve probably noticed that bugs flock around lights at night. “Certain lights attract insects,” says Frick. “Some types of bats take advantage of this and fly into the illuminated area to feed.” It’s like an all-you-can-eat bug buffet. It might sound smart to catch a midnight snack there. But it’s very risky. In well-lit areas, bats are easy targets. Predators such as peregrine falcons and owls can spot them. To stay safe, bats need the cover of darkness.

When bugs gather around electric lights, another problem develops. The glow attracts all those insects, but it also changes their behavior. Brightness charms the creatures so much that they might not mate. That means their numbers decrease over time. And that could spell disaster for bat species that eat insects. Fewer bugs means less food for bats to eat.

TANGUY STOECKLE/BIOSPHOTO/MINDEN PICTURES

A BRIGHT IDEA

True darkness is getting harder to find on our planet. During the past century, electric lighting has made the nighttime sky 20 percent brighter. Recent estimates suggest that 99 percent of Americans and Europeans live under light-polluted skies (see Glowing World). In towns and cities, the glow from electric lighting can make it nearly impossible to see the stars. That’s bad news for stargazers and nocturnal creatures alike.

The type of artificial light flooding our planet is also an issue. The world over, individuals and communities are replacing old types of lights with newer light emitting diodes (LEDs). “LED technology has numerous benefits,” says Porcella, the lighting educator. “LED lights use far less electricity. And they generate light without generating heat. So they’re energy efficient.” Not wasting energy is good for the environment. But LEDs can have a downside.

True darkness is getting harder to find on our planet. The nighttime sky has become 20 percent brighter during the past century. That’s because of electric lighting. Recent reports suggest that 99 percent of Americans and Europeans live under light-polluted skies (see Glowing World). In towns and cities, electric lighting can make it nearly impossible to see the stars. That’s bad news for both stargazers and nocturnal creatures.

Another issue is the type of artificial light flooding our planet. People and communities around the world are replacing older lights with light emitting diodes (LEDs). “LED technology has numerous benefits,” says Porcella, the lighting educator. “LED lights use far less electricity. And they generate light without generating heat. So they’re energy efficient.” Not wasting energy is good for the environment. But LEDs can have a downside.

Wildlife scientists have noticed that certain colors of LED lights, like those with cool-white and bluish hues, seem to bother nocturnal animals. Warmer hues, though, don’t seem to affect wildlife at all (see Light-Pollution Solutions). “These warmer hues have what we call ‘a wildlife-friendly wavelength,’” Porcella explains. Visible light contains many wavelengths. Each wavelength—a measurement of the distance between a light wave’s peaks—corresponds to a different color of light. Wavelengths that produce a reddish tint, which people can see, seem to be invisible to nocturnal animals.

“Bats don’t see red light as particularly bright, if they even see it at all,” says Maurice Donners. He’s an engineer at Signify, the company formerly known as Philips Lighting, who helped invent new bat-friendly streetlights being used in the Netherlands. Because bats don’t perceive the redder light from Signify lamps, they don’t react to it. They follow their natural instincts when they emerge from their roosts at night. Light pollution doesn’t direct how and where they feed or which commuting routes they flap and flutter along.

Wildlife scientists have noticed a problem with certain colors of LED lights. Those with cool-white and bluish colors seem to bother nocturnal animals. But warmer hues don’t seem to affect wildlife (see Light-Pollution Solutions). “These warmer hues have what we call ‘a wildlife-friendly wavelength,’” Porcella explains. Wavelength is a measurement of the distance between a light wave’s peaks. Visible light contains many wavelengths. Each one produces a different color of light. People can see wavelengths with a reddish tint. But these seem to be invisible to nocturnal animals.

“Bats don’t see red light as particularly bright, if they even see it at all,” says Maurice Donners. He’s an engineer at Signify, the company formerly known as Philips Lighting. He helped invent new bat-friendly streetlights being used in the Netherlands. Bats don’t notice the redder light from the Signify lamps, so they don’t react to it. They just come out of their roosts at night and follow their natural instincts. Light pollution doesn’t direct how and where they feed. And it doesn’t control the routes they travel.