Night skies throughout the world are becoming brighter due to humans increasing use of artificial lights. This doesnt simply interrupt our star gazing opportunities it has a significant impact on many different animal species.
The term light pollution generally refers to how urban lighting blocks out our view of the night sky. But researchers are becoming more concerned about whats called ecological light pollution, which alters light levels in terrestrial and aquatic ecosystems. The following are some of their discoveries on the effects of ecological light pollution.
Bird Navigation
Nocturnal bird species use the moon and stars for navigation during migrations. Artificial lighting on tall office buildings, communication towers and other brightly-lit structures has been shown to throw them off-course with often fatal results.
Migrating birds are attracted to artificial lights and will fly in circles around them until they die from exhaustion or predators. Lights also cause a significant number of collisions with human-made structures.
For instance, a 4-year study that concluded in 2007 counted fatal night-time bird collisions at an illuminated offshore research platform in the North Sea. At the end of the study, 767 bird carcasses of 34 different species had been collected. Considering there are over 1,000 human structures in the North Sea, researchers estimated that hundreds of thousands of nocturnal migrating birds could be killed each year in that area alone.
Communication
Some night-dwelling creatures require darkness for proper communication. An example is the complex system fireflies use to communicate messages. The bioluminescent lights they emit from their bodies range from adult mating signals to young larvae warning off predators. These messages can be easily interrupted by stray light.
Darkness is also important for coyote communication. Coyotes howl more during the time of a new moon, when the sky is darkest. They most likely do this to reduce trespassing from other packs or to assist with hunting larger prey during dark conditions. A brighter sky reduces the amount they howl, which could disrupt territorial marking and group hunting coordination.
Reproduction
The reproductive behaviors of many animals may also be altered by light pollution. For instance, female glow-worms use bioluminescent flashes in order to attract males up to 45 meters (150 feet) away. Artificial lights can disrupt these important signals.
Its been found that the female South American tungara frog is less selective about mate choice when greater amounts of light are present. Researchers suggest they may prefer to mate quickly in order to avoid an increased risk of predation in higher light.
Another experiment showed that frogs stopped their mating activity during night football games where a local sports stadium increased sky glow. Frog mating choruses resumed when a shield was put up to block the stadiums light from the frogs habitat.
Ecosystem Interactions
Many predator-prey relationships are dependent on light. One study found that more harbor seals congregated under artificial lights to eat juvenile salmon migrating downstream. When the lights were turned off, the seals ate less salmon. This shows how increased light pollution can disrupt a natural balance, benefitting one species and putting another at risk.
The loss of nocturnal moths is another example of how local ecology can be impacted. Moths are attracted to lights and many are killed annually by touching hot components or getting caught in light-bated electric traps. The bats and birds who feed on them lose a food source. Also, moths play an important role in pollination for many different plant species. These are affected by declining moth populations.
Disorientation
Artificial night lighting may also disorient creatures that rely on darkness for navigation. The disruption of newly hatched baby sea turtles is a well-documented case.
When the hatchlings emerge from nests on sandy beaches, they will naturally move away from the dark silhouettes of vegetation on the beach. This causes them to head towards the open ocean. Beachfront lighting prevents the young turtles from seeing the silhouettes properly, and they become disoriented and remain stranded on the beach exposed to the elements and predators. Millions of hatchlings die this way each year.
What Can Be Done?
Many places throughout the world have taken steps to reduce light pollution. Audubon started a Lights Out program that now includes many major US cities.
In addition, the International Dark Sky Association works to conserve areas with dark skies through public education and designating Dark Sky communities, parks, and reserves. These are all listed on their website and many are open to visitors.
You can also take action at home to reduce ecological light pollution. Some helpful measures include:
Avoid using unnecessary interior or exterior lighting.
Install motion sensors on all outdoor lights. This will also help reduce your electricity costs.
Turn off any lights at night that are not motion sensing.
Take extra care to reduce night lighting during bird migration periods, typically in April and May, and again in August through to November.
Ensure all exterior lighting is fully shielded so light is prevented from shining upwards into the sky. These fixtures may also be called zero light up or dark sky compliant. The International Dark Sky Association has further information on types of fixtures to look for.
Use yellow or red lights when possible. These have a lower impact on wildlife and dont attract insects.
Install window coverings that block as much light from escaping as possible.
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Disclaimer: The views expressed above are solely those of the author and may not reflect those of Care2, Inc., its employees or advertisers.
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