Photo by Mark Warot.

August 1, 2023

Starry Nights: A Story of Wildlife and Light Pollution

Twinkle, twinkle little star. ‘Cause in a sky full of stars. Starry, starry night. Familiar with any of those song lyrics? Music is one way that we share what is important to us. Though it’s no secret that people have long been enamored of star gazing. And each night as I scan the stars from my backyard, I’m grateful to have such an opportunity. It’s a view many people can no longer fully experience.

Researchers have shown that about 83 percent of the world’s population and more than 99 percent of the U.S. and European populations live under light-polluted skies. Meaning it’s getting harder for most of us to experience a beautiful, star-filled sky. But it isn’t just beauty and inspiration for song lyrics that we’re being deprived of; light pollution causes a bevy of unintentional impacts for people, plants and wildlife.

Light Pollution

Light pollution is caused by the artificial brightening of the environment from excessive light. We’re talking about light from humanmade sources such as streetlights and buildings as opposed to naturally occurring light such as moonlight. The right kind of light in the right amount in the right place is not the problem. The problem is an excess amount of light or light in the wrong places.

Light pollution comes in many forms, so studying its impacts is not an easy task. Skyglow is the haze of light that occurs over urban areas caused by light being scattered by water droplets, dust or other particles in the air. It’s the “glow” over cities that can block our view of the stars. Light trespass happens when unwanted light, say from a neighbor’s outdoor security lighting, illuminates an adjacent property that would otherwise be dark. Glare is created by light that shines horizontally, such as from vehicle headlights. Over-illumination happens when more light is used than is needed for a specific activity, for example, an empty office building keeping the lights on all night.

Impacts of Artificial Light at Night

Along with documented threats to human health and economic impacts, light pollution has many disruptive effects on natural processes. People, plants and animals are adapted to a day to night cycle. And many behaviors of wildlife including foraging, hunting, daily movements, migration and mating are all cued by light. Artificial light at night (ALAN) disrupts these cues in two main ways. First, we’ve disrupted where, when and how much light occurs at night over much of the earth. Second, the lights we use are in a spectrum that is different from natural light sources such as sunlight, moonlight, or starlight.

A growing body of research reveals that ALAN disrupts natural cues for a myriad of plants and animals. For those who are interested in exploring this topic in depth, a great place to start is the book Ecological Consequences of Artificial Night Lighting edited by Catherine Rich and Travis Longcore. And for those wishing to drop further down the reading rabbit hole, the article Human Alteration of Natural Light Cycles: causes and ecological consequences provides a good overview of the effects of light pollution and will lead you on the path to many other research articles.

A map of the United States showing the prevalence of nighttime lights. The eastern half of the US is dominated with light as is the west coast.
A map of the US shows the distribution of light across the country. Photo by NASA.

Wildlife and Light Pollution

ALAN has been widely documented to have effects on the physiology and behavior of individual organisms, and we’ll dive into a few examples below. But the impacts of ALAN at the level of populations, communities and ecosystems is not as well understood. What scientists are slowly teasing out is that ALAN appears to make some habitats unusable for some animals, improves hunting success for others, and can create barriers to or sometimes connect movement corridors through the landscape. In some cases, it does all of those things at once. For example, streetlights that attract insects and illuminate nearby natural areas attract some species of bats, but deter other species of bats from using the area.


Many of us are familiar with the effects of light pollution on sea turtles. Artificially bright beaches can discourage females from nesting, or those that do come ashore to lay their eggs can become so disoriented by lights that they wander onto nearby roadways, often with fatal results. The sea turtle hatchlings can also become disoriented and navigate toward the artificial light sources, never finding the sea. Those that do eventually figure out which direction to go often arrive at the ocean suffering from dehydration and exhaustion, which biologists think may make them more susceptible to predation.


There have been at least 50 studies conducted on the effects of ALAN on birds. Results of these studies highlight the complexity of understanding long-term impacts of too much light. In one study, ALAN improved nighttime foraging of shorebirds. In another study, captive birds exposed to light at night developed their reproductive systems up to one month earlier than birds kept under dark nights and they also molted one month earlier. The CICADA website discusses the challenges that light pollution poses to migrating birds.


The eyes of most nocturnal mammals have evolved to have large pupils to let in lots of light and rod-rich, but cone-poor, retinas that help them see better during low light conditions. These adaptations work efficiently under natural nighttime conditions, but bright lights, such as the glare of headlights, temporarily blind most nocturnal mammals, decreasing their chance of survival as they cross roadways. Small mammals, such as deer mice, have been shown to decrease their movements and food consumption in areas with increased artificial lighting, similar to what is experienced under streetlights along roadways. Other ways that light pollution affects mammals in the environment include disruption of natural foraging patterns, increased predation risk, disruption of biological clocks, and disruption of dispersal movements.

Turn the Lights Out

Curbing excess lighting could significantly reduce light pollution. The National Park Service and the International Dark-Sky Association both have lots of simple tips for reducing light pollution, such as:
• Only use lighting when and where it is needed.
• If safety is a concern, install motion detector lights and timers.
• Properly shield all outdoor lights.
• Keep blinds drawn at night to keep light inside.

BirdCast allows you to see when bird migration is happening in your area and to monitor for peak migration dates.

Hello Darkness My Old Friend

Sometimes it is the little things that have the biggest impacts. One person writing down a song lyric turns into millions of people knowing and loving a song. One person turning off unnecessary lights can lead to millions of people doing the same. Darker nights. Starry, starry skies. Wildlife going about their business under the cover of moonlight instead of skyglow. Now that would be something to sing about.

Laura Kammin is an Education Programming Specialist with the National Great Rivers Research and Education Center. She formerly held positions at Illinois-Indiana Sea Grant, University of Illinois Extension, Prairie Rivers Network and the Illinois Natural History Survey. She received her master’s degree in wildlife ecology from the University of Illinois, Urbana-Champaign.

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