Hello from Miami, Florida! I am busy pursuing my marine conservation studies at University of Miami, Rosenstiel School of Marine and Atmospheric Science, but I wanted to take a quick moment to share some information about light pollution and how it affects wildlife. This information is from a virtual event hosted by Tropical Audubon Society in celebration of Miami Dark Sky Week 2021.
This article is a synthesis of all the information featured in this event from Dr. Frank Ridgley from Zoo Miami Conservation and Research, Dr. Oliver Keller from the Florida Department of Agriculture and Consumer Services, Brian Rapoza from Tropical Audubon Society, Dr. Melquisedec Gamba-Rios from Bat Conservation International, and Leanne Hauptman from the Miami-Dade County Sea Turtle Conservation Program. Although the examples of light pollution are concentrated on tropical animals often found in or near the Miami area, the lessons can be applied to all wildlife globally.
Light pollution is generally defined as the presence of anthropogenic and artificial light in the night environment; and/or the inappropriate or excessive use of artificial light. It can be classified into four separate categories: glare, skyglow, light trespass, and clutter. Glare is the excessive brightness that causes visual discomfort, which is something we humans are familiar with when driving and someone is blinding us with their high beams. Skyglow is the brightening of the night sky over inhabited areas. Most of us are familiar with this type of light pollution because we live in or near large cities. It often blocks us from seeing the stars at night and experiencing actual darkness during the night. Light trespass is defined as light falling where it is not intended or needed. Again, we have all experienced this at some point in our lives, as this is typically when a street lamp lights up way more than the street itself. The final category is clutter and is defined as bright, confusing, and excessive groupings of light sources. This is often seen in cities with a lot of night time activities like in New York City (“the city that never sleeps”), Philadelphia, and Atlantic City with all of their business signs lit up at night.
Researchers have compared the human visual color spectrum to that of other animals, and have found that many animals can see purples, blues, and greens. A few can see yellows, oranges, and reds, and nearly all of them can see some form of ultraviolet. This information is important because it tells us what type of light affects wildlife more than others, and can serve as a guiding tool for light selection. For instance, white LED lights have more blue light in them which affects wildlife at night since most of them can see it, but switching to a filtered LED light will remove the blue portion of the light. Using light shields to direct light to only where it needs to be makes a huge difference.
Okay, so wildlife can see these lights, but how does it actually affect them? This is a good question, and it is one that many researchers have spent time studying over many years across various species. Light pollution can affect wildlife reproduction, sleep cycles, predator-prey interactions, migration, prevention of seasonal plant changes, reduced survivorship, attraction or repulsion, and physical health. The effects vary per species, as usual, and some species are affected in more than one category as it depends on their life history.
For fireflies and other nocturnal insects, navigation through the night is guided by the moonlight or starlight. Outdoor lights are often mistaken for these navigational lights, which is why we often see insects flying around outdoor lights. They become confused and stuck in the cyclic migration around the light because they do not know the difference between artificial light and their navigational lights. They circle for hours, wasting precious energy and eventually die. Some may be lucky enough to get out of the cycle, but will become trapped by another outdoor light. This has become a major contributor to what scientists are now calling the insect apocalypse. Instead of these insects, foraging, mating, and migrating, they get stuck in the light and die. Thus, they are not fulfilling their crucial roles in their respective ecosystems.
Regarding birds, light pollution affects the nocturnal species, but researchers have found that migrating songbirds are affected the most. Millions of songbirds travel thousands of miles between their nesting habitats in the northern part of North America and their wintering grounds in the southern parts of North America. These migrations are generally categorized into four flyways: Atlantic, Mississippi, Central, and Pacific. The one of most importance to New Jersey is the Atlantic Flyway, which is used by many thrushes, orioles, 30-40 warblers species, tanagers, buntings, and grosbeaks to name a few type of songbirds. Nocturnal migration is advantageous because of the cooler temperatures, calmer air, and to avoid predators. They use an array of navigational guides, which include starlight. Light pollution causes songbirds to get disoriented and they often get lost in cities which leads to building collisions when they are exhausted and trying to find refuge.
Bats are able to see colors and ultraviolet light and, like many other species, rely on moonlight for navigation. The intensity of the moonlight will determine how high bats will fly regarding tree canopies to avoid predation. Bats will fly above the tree canopies in low moonlight because their predators will not be able to see them well, and below the tree canopy when moon light is high. Light pollution is bright and in a sense acts like high moonlight, which bats try to avoid because they do not want to be eaten. As a result, researchers are findings that bats stay hidden in the darker areas of urban settings, but these areas are fragmented by light pollution. This is a form of habitat fragmentation because normally the bats would fly over the entire region if there was no light pollution. In some urban settings these darker spaces are separated by large areas of light pollution, which essentially isolates individuals to a small location and makes it hard to find food and mates.
Sea turtles are another species affected by light pollution when the females come to land to nest and when the hatchlings make their way to the oceans. Sea turtles use the reflection of moonlight and starlight off the ocean to differentiate between the dark dunes of sand at night and the reflective ocean so they know which way to travel. Light pollution causes nesting female sea turtles to become disoriented and then lost, often wandering into areas where they are vulnerable to humans and predators. They also waste enormous amounts of energy while moving along land, so getting lost can lead to their deaths. Furthermore, this may deter a female from laying her eggs. Regarding the hatchlings, light pollution often tricks them into thinking that they are heading towards the ocean, when in reality they are often heading towards busy roads or other urban areas and never make it back to the ocean.
There are lighting guidelines to help reduce light pollution and often they are easy things to incorporate into our homes, neighborhoods, and cities. It is just a matter of getting people to care enough to make the changes to help wildlife. The first step is to start with natural darkness and only add light for specific purposes. Second step is to use adaptive light controls to manage light timing, intensity, and color. Third step is to only light the object or area intended by keeping the lights low, directed, and shielded. Fourth step is to use the lowest intensity lighting needed. The fifth step is to use non-reflective, dark-colored surfaces so the light does not shine elsewhere off objects. The sixth and final step is to use lights with reduced or filtered blue, violet, and ultra-violet wavelengths.
Next time you see a lamp, stop for a moment and think about its purpose and where the light shines. Frequently you will find that the light goes way beyond its intended purpose. Think about the wildlife in the area, and use your new knowledge about light pollution to problem solve the situation. Analyze the lights around your house and your community. Unless you are in an environmentally friendly town (super rare, by the way), you will find light pollution everywhere from all four categories. How will you help wildlife navigate safely through the night? How will you contribute to a healthy ecosystem, in which we humans also need in order to survive?
I hope you find this information useful and feel inspired to make applicable changes to reduce light pollution and help wildlife navigate safely through the night. For the full experience of this Tropical Audubon Society virtual event, check out its recording on YouTube: https://youtu.be/dvGUqaZ5Drg
Written by Denise Hassinger, MSc., FCW Treasurer