Where you live, are you able to see the Milky Way? What about Sirius, the brightest star in our night sky? Can you see any stars at all?
As humans have expanded our civilizations laden with electricity, we have also illuminated the night sky. In 2016, it was found that about ⅓ of people on Earth are no longer able to see the Milky Way. What does this increased light mean for wildlife?
The growing amount of light in our sky affects many species in many ways. From moths to fish to songbirds, species we may not even think about are being affected by our artificial light. A popular example to draw attention to light pollution and man-made negative effects on animals is the plight of sea turtles.
Sea turtle species lay their eggs on the same beaches each year. When the eggs hatch, the babies find their way to the ocean by following the light of the moon reflecting off of the water. This changes when beachside homes, cities and roads are present. The baby sea turtles try to make their way towards the artificial light instead of the moonlit ocean. Many never make it to the ocean and, unfortunately, die. Still, the mother sea turtle’s instincts will cause her to return to this same beach each time she is due to lay a clutch of eggs. All of her babies will therefore face the same challenge.
An interesting example of how light pollution affects many aspects of a species’ life cycle is songbirds. As many of us know, songbirds are some of the first critters to wake up in the morning. If you notice some species calling earlier than others, this is due to their circadian rhythms. All animals have circadian rhythms, the cycle of sleeping and waking each day along with changes throughout the day like body temperature and hormone levels. The sun rising in the morning triggers the songbirds’ bodies to wake up and start their day.
However, if they are exposed to man-made sources of light at times that do not correspond with the sun, it will cause a shift in this rhythm. Both internal processes and behaviors can be affected. Birds not normally active at night may still be awake or a bird’s typical daily activities may change all together. Changes in behavior can affect their ability to interact with others of their species for reproduction, put them in contact with unfriendly predators, or hinder their opportunities to find food. The phrase “the early bird gets the worm” may no longer apply.
Light pollution becomes a major issue when it comes to a very important bird activity–flying. During normal daily flight, significant light interference can cause disorientation and collisions. Twice a year, migrating birds fly and navigate for miles and miles to avoid winter weather or to return to their summer homes. There are many methods identified when it comes to how birds navigate during migration. Different species have different methods or use a combination of multiple. The ones affected by light are the sun compass, the star compass and the utilization of landmarks.
Birds that use the sun during the day do so by sensing and understanding its position in the sky and matching its compass direction. This method is tied in with their circadian rhythm. Research about the star compass has found that birds can orient themselves to a north-south orientation based on the positions of the stars. Of course, their ability to see the stars is of great importance. Beyond clouds, light pollution in a populated area can lighten the night sky so much that stars aren’t visible. Disorientation, as a result, can affect a flock’s migration pattern, timing, and distance.
Finally, some birds use visual landmarks such as mountains or bodies of water to navigate. If there is a source of artificial light that obscures the bird’s view of a landmark, they may get disoriented on their path. Landmarks are also useful when flocks are finding a good resting habitat on their migration. If they cannot find a suitable resting habitat it might put them in danger of exhaustion or predation.
Frog and toad species have also been found to be negatively impacted by light at night. As nocturnal amphibians, most of the vital activities of frogs and toads happen at night. Namely, calling for mates and reproduction are disrupted with the introduction of additional light. A 2018 study showed that artificial light caused wood frog eggs to hatch at a lower success rate and that metamorphosis was affected. Tadpoles in artificial light were less active and more susceptible to parasites and chemicals, an issue that amphibians are already sensitive to.
Overall, the result of light pollution in impacted species is a lower chance of individual survival and/or reproduction opportunities. This means man-made light sources are causing declines in populations of many species of animals that are vital to their ecosystems and our planet.
So what can be done to combat this important issue? Education is essential so that more people know about the issue of light pollution and can take steps to make changes to their own homes or workplaces. C&W Energy Solutions suggests the following adjustments for individuals to make:
- Keep light fixtures as low as possible
- Have a shield on light fixtures so the emitted light is angled downwards
- Have lights that do not emit as much blue light or have blue light filters
- Install dimmers and timers on lights
While convenient for human life, illuminating the dark is harmful to animals–including ourselves. As communities continue to grow and technology advances, we must be mindful in our choices to become a part of the solution, not the problem.
