Romantic attraction or fatal temptation? Who are the night lights affecting subtly?

Artificial light at night can change the behavior of all animals, not just humans

Nocturnal behaviour is increasingly threatened by the presence of artificial lighting.

Illustration: A sea turtle is migrating.

This article was originally published in The Conversation. The publisher of the book submitted it to Space.com's Expert Voices: Op-Ed & Insights.

Therésa Jones is an associate professor of evolution and behavior at the University of Melbourne.

Kathryn McNamara is a postdoctoral researcher at the University of Melbourne.

As the moon rises on a warm early summer evening, thousands of baby sea turtles emerge to begin their perilous journey to the ocean, while millions of moths and fireflies take to the air and begin their complex search for a mate.

These nocturnal behaviors, and many others like them, evolved as an adaptation to the darkness of the night. Today, however, they are under increasing threat from human illumination.

Essentially, artificial light at night (such as street lamps) masks the natural light cycle. Its presence blurs the transition from day to night and can suppress the natural cycle of the moon. We are gradually realizing that this has huge physiological and behavioral consequences, including changes in hormones related to the diurnal cycle of some species and their seasonal reproduction, as well as changes in the timing of daily activities such as sleeping, foraging or mating.

The intensity and spread of artificial light at night are increasing (estimated at 2-6% per year), making it one of the fastest growing pollutants worldwide. Its presence is associated with changes in the structure of animal communities and a decline in biodiversity.

How are animals affected by artificial light?

Light at night can both attract and repel animals. Animals living in urban environments are often attracted to artificial light. Sea turtles are drawn inland from the safety of the ocean, where they can be run over by vehicles or drown in swimming pools. Thousands of moths and other invertebrates are swirled around by city lights, becoming disoriented until they fall to the ground or die if they can't find a mate. Female fireflies secrete bioluminescent signals to attract mates, but this light can't compete with street lighting, so they also may not be able to reproduce.

Every year, it is estimated that millions of birds are injured or killed by being caught in bright city lights, becoming disoriented, colliding with bright buildings, or being drawn from natural migration paths into urban environments where resources and food are limited and predators are more numerous.

Some other animals, such as bats and small mammals, flee from lights, or may avoid them altogether. City lights drastically reduce the habitats and resources they need to live and reproduce. For these species, street lighting means habitat destruction, as a light or a road (or both) cuts off the darkness they need in their natural habitats. Humans can retreat to their homes to avoid lights, but wildlife may have no choice but to leave.

Nighttime lights do have some benefits for some species. Species that are normally active only during the day can extend their foraging time. Nocturnal spiders and geckos are often found around lights, where they can eat the large numbers of insects that are attracted to them. While these species may appear to be profiting, this doesn't mean it's not harmful. Studies have shown that when insects and spiders are exposed to light for long periods of time at night, their immune systems are weakened, their health is threatened, and their growth, development, and number of offspring are altered.

Bird migration is the longest journey in the animal kingdom, and migratory birds face many dangers along the way, including light pollution. To help them, we must take action.

How do we fix it?

In Florida, city beaches are lit with amber lights, which are less attractive to turtles, and lights are turned off during the turtles' resident season. Phillip Island is home to millions of short-tailed shearwaters. Many of the lights there are also amber, and lights are turned off along the migratory route during the feathering season to reduce mortality.

Two art installations called "Tribute in Light" were installed on the original site of the World Trade Center in New York. They consist of 88 vertical high-intensity spotlights with a range of up to 100km. They are lit up on the anniversary every September. However, when it was realized that this was also the migration season for migratory birds in North America, the New York City government changed it to turning on the lights for one hour and then taking a 20-minute break to allow lost birds and bats to escape and reduce the attraction to migratory animals.

These strategies have significantly reduced the ecological impact of night lights on animals, saving countless lives.

More than 200 regions around the world have called for the return of dark nighttime skies to combat light pollution that separates people and animals from the starlight.

While these targeted solutions are effective, they will not solve another global biodiversity crisis. Many countries have outdoor lighting standards and some guidelines have been established, but these guidelines are not enforceable.

As a member of the Earth, we also have the ability to help animals, such as:

In a sense, fixing the effects of nighttime lighting is simple: we just need to turn off the lights and let the natural moonlight gently illuminate the night.

But logically, this is the least feasible, because night lights were invented to meet the needs of a small number of people who do not want to live only by natural light at night. When we cannot change the fact that we turn on lights at night, we also have other ways to reduce the impact. For example, limit the number of lights, reduce the intensity of lights, reduce the lighting time, or change the color of lights. Different animals have very different sensitivities to different colors of light. Some research reports indicate that red and amber lights have less impact on animals, while blue and white lights have greater impact on animals.

BY:Therésa Jones

FY: Jingli

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