Light Pollution
Lights, Leaves, Bugs, and Birds
Artificial light at night disrupts the natural rhythms of wildlife. Birds, insects, amphibians, and plants all depend on the cycle of day and night. Reducing unnecessary lighting can protect migrating birds, preserve insect populations, and restore the nighttime environment.
Until relatively recently in Earth’s history, all life relied on the predictable rhythm of day and night. Plants and animals depend on Earth’s daily cycle of light and dark to govern reproduction, finding food, sleep, and protection from predators. Scientific evidence suggests that artificial light at night has negative—and sometimes deadly—effects on many creatures, including amphibians, birds, mammals, insects, and plants.
- Artificial light at night disrupts wildlife behavior and reproduction.
- Night lighting harms migratory birds and increases collision risk at lighted buildings.
- Light attracts and kills nocturnal insects, reducing the caterpillars nesting birds depend on.
Why Light Pollution Matters
Artificial lights affect wetland habitats, home to amphibians whose nighttime vocalizations are part of breeding rituals. Lights can disrupt this activity, interfering with reproduction and reducing populations of frogs and toads.
Birds migrating at night use celestial navigation to find their way. Artificial lighting can interfere with their ability to navigate and can also draw birds toward lighted buildings, increasing the risk of window collisions.
One of the most far-reaching impacts for birds involves insects. Many insects—upon which birds depend—are drawn to light, creating a fatal attraction. Most songbirds require caterpillars to raise their young. There are about 12,000 types of North American moths and about 825 butterfly species. Most moths are nocturnal, and many are drawn to lights where they may die, reducing the essential caterpillar populations nesting birds need.
How to Mitigate the Effects of Light Pollution
- Learn to appreciate the role of insects in our natural world.
- Use lights that are shielded so they direct light downward.
- Light only what needs to be lit—and only when it needs to be lit.
- Use energy-efficient bulbs, only as bright as necessary.
- Choose warm white or yellow bulbs rather than harsh blue-white light.
- Use motion detectors so lights are not always on.
- Replace mercury vapor lights with yellow LEDs.
- Use coverings on windows when lights are on inside.
Bug Zappers
Bug zappers are not effective at killing mosquitoes. Biting insects are attracted primarily to the carbon dioxide emitted by humans rather than to light. As a result, zappers can draw insects into the area where people are present without meaningfully reducing bites.
Bug zappers are an effective way to kill moths. Adult moths are attracted to the light. When moths try to reach the bulb, they fly through the safety cage and into electrodes that kill them. Because moths become caterpillars—and caterpillars are essential food for nesting birds—killing moths reduces the food web birds depend on.
About Tent Worm Caterpillars
Although generally disliked, tent worms are an important food source for birds. They typically will not kill healthy trees. If trees are vigorous, they can usually tolerate defoliation and recover.
Leaves and Moths
Many butterfly and moth species spend the winter in fallen leaf litter. Luna moths, Great Spangled Fritillaries, woolly bear caterpillars (Isabella Tiger Moths), and Red-banded Hairstreaks are just a few examples. Some species overwinter as eggs, others as pupae, and some as adults.
To help moth and butterfly caterpillars, do not rake your leaves. Leaving leaf litter in place preserves overwintering habitat and helps sustain the insects that birds rely on.