Teresa Jones (opens in new tab)Associate Professor of Evolution and Behaviour, University of Melbourne
Catherine McNamara (opens in new tab)Postdoctoral Research Fellow, University of Melbourne
As the moon rises on a warm early summer evening, thousands of baby turtles emerge and begin their precarious journey to the ocean, while millions of moths and fireflies take to the air to begin the complex process of finding a mate.
These nocturnal behaviors and many others like them have evolved to take advantage of the darkness of night. But today they are under increasing threat from the presence of artificial lighting.
Connected: Can you see stars in a light polluted sky?
Basically, artificial light at night (such as from street lights) masks natural light cycles. Its presence blurs the transition from day to night and can delay the natural cycle of moon. We are increasingly realizing that this has dramatic physiological and behavioral consequences, including changing the hormones associated with the day-night cycles of some species and their seasonal reproduction, as well as changing the timing of daily activities such as sleep, foraging or mating (opens in new tab).
The increasing intensity and spread of artificial light at night (estimates suggest 2-6% p.a (opens in new tab)) makes it one of the fastest growing global pollutants. Its presence is associated with changes in the structure of animal communities (opens in new tab) and reducing biodiversity (opens in new tab).
How animals are affected by artificial lighting
Light at night can both attract and repel. Animals living in urban environments are often attracted to artificial lighting. Turtles can turn away from the safety of the oceans and head for land, where they can be run over by a vehicle or drown in a swimming pool. Thousands of moths and other invertebrates become trapped and disoriented around city lights until they fall to the ground or die without ever finding a mate. Female fireflies produce bioluminescent signals to attract a mate, but this light cannot compete with street lighting, so they may also fail to reproduce.
It is evaluated every year millions of birds (opens in new tab) are injured or killed because they are caught in the rays of bright city lights. They are disoriented and crash into brightly lit structures or get abducted from them natural migration routes (opens in new tab) in an urban environment with limited resources and food and more predators.
Other animals, such as bats and small mammals, avoid lights or avoid them altogether. This effectively reduces the habitats and resources available for life and reproduction. For these species, street lighting is a form of habitat destruction, where light rather than a road (or perhaps both) cuts through the darkness necessary for their natural habitat. Unlike people who can go back into their home and block out the lights, wild animals may have no choice but to leave.
For some species, light at night does provide some advantages. Species that are normally only active during the day may extend their foraging time. Nocturnal spiders and geckos often visit places around lights because they can feast on the multitude of insects they attract. However, while these types may win on the surface, that doesn’t mean there aren’t hidden costs. Studies with insects and spiders show that exposure to light at night can have an effect immune function (opens in new tab) and health and change theirs growth, development and number of offspring (opens in new tab).
Bird migrations are some of the longest journeys undertaken by any animal, and migrating birds face many dangers along the way, including the effects of light pollution. To protect them, we must #DimLightsForBirds. #WorldMigratoryBirdDay 🕊️🐧: https://t.co/DMCitMNUl5 pic.twitter.com/F0VNGzPswNMay 16, 2022
How can we fix this?
There are some real examples of effective mitigation strategies. In Florida, many urban beaches use amber lights (which are less attractive to turtles) and turn off the street lights (opens in new tab) during turtle nesting season. On Phillip Island, Victoria, home to more than a million short-tailed petrels, many new street lights are also amber and excluded along known migration routes (opens in new tab) during the fledging period to reduce mortality.
In New York, the Tribute in Light (which consists of 88 vertical spotlights that can be seen for nearly 100 km) is turns off for periods of 20 minutes (opens in new tab) to allow disoriented birds (and bats) to escape and reduce the attractiveness of the structure to migratory animals.
In all cases, these strategies have reduced the ecological impact of nighttime lighting and saved the lives of countless animals.
Over 200 places around the world have reclaimed Dark Sky status, challenging the light pollution that has prevented people and animals from accessing the darkness of the starlit night sky. https://t.co/chNvY5ze4IJuly 1, 2022
However, although these targeted measures are effective, they will not solve what could be yet another global biodiversity crisis. Many states have outdoor lighting standards and several independent guidelines have been written, but these are not always applicable and are often open to interpretation.
As an individual, there are things you can do to help, such as:
In a sense, light pollution is relatively easy to fix – we can just turn off the lights and let the night be lit naturally by moonlight.
Logistically, this is mostly not feasible, as the lights are used for the benefit of people who are often reluctant to give them up. However, while artificial light allows humans to use the night for work, leisure and play, in doing so we are catastrophically altering the environment for many other species.
Short of turning off the lights, there are other management approaches we can take to mitigate their impact. We can limit their number; reduce their intensity and the time they are on; and potentially change color. Animal species differ in their sensitivity to different colors of light, and research shows that some colors (amber and red) may be less harmful than the blue-rich white lights that are becoming common around the world.
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