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Column: Light pollution can affect your circadian clock

Jan Conley1 / 2
This photo taken on Skyline Parkway the night of Sunday, Dec. 1, shows the lights of downtown Duluth. (Photo courtesy Trudy Vrieze)2 / 2

Light. In the north country we like daylight hours when we can accomplish our tasks. We take walks, plant our gardens and enjoy outdoor activities.

At night we wind down, go indoors and turn on our lights. Later we sleep. Some of us sleep in complete darkness with shades drawn and no inside lighting, while others sleep with lights flickering from without and within their homes.

At Hawk's Ridge in Duluth, we see many birds that use light from the moon, stars and setting sun for navigation during their twice-yearly migrations, but light pollution can obscure the skies. City lights can make it difficult for them to see landmarks and they may be drawn to artificial light, flying around and around until they can fly no more.

Every year more than 100 million birds in North America die in collisions with lighted buildings and towers.

It happens in Duluth, too. The lucky ones are brought to Wildwoods to be rehabilitated and released.

Birds are not the only ones whose rhythms are disrupted by light.

Scientific studies show that humans, animals, and plants have a circadian clock that requires regular periods of light and dark. This clock affects bodily functions such as hormone production and cell regulation.

According to a 2009 article, "Missing the Dark: Health Effect of Light Pollution," disrupting these rhythms causes insomnia, depression and obesity, and may be a factor in illnesses such as cancer, diabetes and heart disease. This article was published the U.S. National Institutes of Health.

For backyard animals such as nocturnal suburban wildlife -- raccoons, foxes, bats, flying squirrels -- light at night is also a problem.

Many mammals hunt at night and are affected adversely by artificial light.

Light exposes them to predators and reduces the time they have to find food, shelter and mates. Mammals avoid hunting in open areas even when the moon is bright. A constant artificial light at night restricts their foraging and can cause malnutrition.

Reptiles such as turtles are especially affected by light pollution.

When hatchlings emerge, they instinctively crawl towards light, which they think is water reflecting the light of the moon and stars. Artificial light may cause them to crawl toward a yard or community, keeping them from the safety of water and putting them at risk of predation or being run over.

Amphibians such as frogs are an important part of wooded and aquatic ecosystems. Light pollution may be a contributing factor to the global decline of amphibians, since many are nocturnally active and have biological rhythms regulated by light. A study in Syracuse, New York, found that male frog calls are decreased when artificial light is present, affecting reproduction.

We have all seen moths fluttering around an outdoor light. They expend energy and are distracted from mating and migration.

Moths may fly toward lights and remain there all night. That comes at

a high cost, including lost reproductive opportunities.

This is especially crucial to those adult species that live for only a week. Moths are pollinators and their loss affects the viability of our fruits and flowering plants.

Many cities, including Minneapolis and St. Paul, are part of a program working to reduce night-time lighting. The International Dark Sky Association is a worldwide organization whose mission is "to preserve and protect the night-time environment and our heritage of dark skies through quality outdoor lighting."

They work to make businesses and the public aware of the need to turn off unneeded lighting. We could learn from their efforts and apply it to our own backyards and businesses in the Duluth area.

What can we do as individuals to help animals ... and ourselves?

Simple options include using outdoor lights only when needed. Don't light up the outdoors when you are inside.

Use bulbs that are lower wattage, only what you need to get the job done.

When everyone has returned home, shut off the yard light. Shield your lights and make sure they are focused down, not pointed skyward.

Finally, for your own health, eliminate all lights from your sleeping area.

Tomorrow the sun will shine, but for tonight, let the Northland be dark.

Wildwoods is a 501(c)(3) wildlife rehabilitation organization in Duluth. For more information on wildlife and how you can help, including volunteer opportunities, visit

Jan Conley is a former teacher and environmental nonprofit founder as well as a hiker and bird watcher. She is an active volunteer at Hawk Ridge in Duluth and in the Florida Everglades.