Dawn Chorus friends, I’ve started my transition moving from Idaho to Montana, so life is a bit crazy right now. For today’s DC I’m reprising an article I wrote a couple years ago (for a different blog) calling attention to ecological light pollution and its effects on our feathered friends, particularly during migration. I hope you’ll find the diary ‘illuminating’ – in a good way!
Map of North America’s artificial sky brightness. Black = pristine; gray = some sky glow; blue = skies polluted on an astronomical level; yellow = winter Milky Way obscured; red/white = true night completely masked by artificial twilight (Falchi et al. 2016).
For millions of years, animals have relied on Earth’s predictable rhythm of day and night. This dark-light cycle governs many life-sustaining behaviors encoded in the DNA of all animals. In the mere span of the last century, the increasing proliferation of artificial lights has transformed the nighttime environment over large portions of Earth’s surface, not only obscuring our ability to marvel at the heavens, but also causing disruptions to animals dependent on the darkness of night. The phenomenon prevents nearly 80% of people in North America from seeing the Milky Way galaxy in the night sky.
The intrusion of artificial light on the nighttime setting is known as light pollution. It is pronounced around urban centers, creating “sky glow”—the scattering of light by clouds and atmospheric particles that makes it difficult to see stars and other features of the night sky. Light pollution also includes any outdoor light that creates glare, clutter (bright, excessive grouping of light sources), or light trespass (intrusive light). Its sources include exterior and interior lighting on buildings, billboard advertising, commercial properties, offices, factories, streetlights, and illuminated sporting venues. These sources generate “ecological light pollution,” which is artificial light that alters the natural patterns of light and dark in ecosystems.
Sky glow from Coachella Valley, Riverside County, CA as seen from Joshua Tree National Park.
Ecological light pollution is a potent influence on the behavioral ecology of organisms in natural systems. Light pollution causes disorientation, misorientation, and attraction to and repulsion from the altered light environment, which in turn may affect how animals move about, communicate, find food, and even select mates.
Fall migrating birds ‘trapped’ by the 9/11 Tribute in Light.
Birds have been migrating great distances for millennia, navigating by the sun, moon, and stars, prominent landmarks, and the Earth’s magnetic field. Many species have evolved to migrate at night when they are less vulnerable to predation and skies are usually less turbulent. Urbanization with its ever-present glow of artificial light has turned nighttime skies into perilous pathways for migrating birds. As they fly over brightly-lit cities and suburbs, birds can become confused and disoriented by urban lights, particularly lights on high buildings and other structures (e.g., telecommunication towers) directly in their paths. They may collide with structures or become trapped in beams of light where they circle gyre-like until exhausted and land in unsafe locations. If grounded, reflective glass and bright interior lighting can leave them vulnerable to other urban threats. These dangers are magnified on foggy or rainy nights when cloud cover is low and birds migrate at lower altitudes.
In part due to light pollution impacts, building collisions are among the top human-caused threats to birds, killing an estimated 100 million to 1 billion birds annually across North America.
A case in point is the 9/11 Tribute in Light, illuminated every September 11 since 2002. The beams are sharply visible from 60 miles away and project four miles into the sky over New York City. If environmental conditions are right, potentially millions of night-migrating birds can be drawn into the light beams, creating an avian traffic jam of confused and disoriented birds.
Ornithologists monitor bird behavior at the Tribute each year. The monitoring protocol states that if one or more birds crashes to the ground, dead; OR if birds appear to be trapped (flying low in the beams and calling); OR if 1,000 birds are in the beams for >20-minute period, then the Tribute lights are shut off for 20 minutes to allow them to fly on.
Bright City Lights = Dangerous Flights
Researchers at the Cornell Lab of Ornithology describe North American bird migration as:
An invisible river of animals, rivaling any scene from the Serengeti but consisting of half-ounce birds that pass quietly overhead, in the dark.
This river of birds funnel through migratory routes that vary in spring and fall. Many routes directly intersect with major metropolitan areas, creating a perfect (and potentially lethal) storm for avian migrants. A 2017 study by researchers at the Cornell Lab of Ornithology ranked metropolitan areas based on light pollution and geography where birds are at greatest risk of building collisions. They found the same three large cities in the central U.S. — Chicago, Houston, and Dallas — top both spring and fall lists of most dangerous cities for birds.
Migratory flyways of North America & Central America
"Chicago, Houston, and Dallas are uniquely positioned in the heart of North America’s most trafficked aerial corridors. This, in combination with being some of the largest cities in the U.S., make them a serious threat to the passage of migrants, regardless of season," notes study lead author Kyle Horton, a Rose Postdoctoral Fellow at the Cornell Lab.
In spring of 2017, nearly 400 migratory birds were killed by colliding with a 23-story flood-lighted building in Galveston, Texas in a single night. Among the casualties were (from left to right) Blackburnian Warblers, Ovenbirds, and Magnolia Warblers.
Most Dangerous Cities for Birds
Spring Migration Fall Migration
- Chicago 1. Chicago
- Houston 2. Houston
- Dallas 3. Dallas
- Los Angeles 4. Atlanta
- St. Louis 5. New York
- Minneapolis 6. St. Louis
- Kansas City 7. Minneapolis
- New York 8. Kansas City
- Atlanta 9. Washington DC
- San Antonio 10. Philadelphia
Lights Out Initiatives
To reduce bird collisions during migration, Audubon chapters, the Fatal Light Awareness Program (FLAP), and other conservation groups have launched dozens of “Lights Out" initiatives across the U.S. and Canada. These voluntary programs encourage cities, businesses, agencies, and homeowners to turn off or reduce lighting during migration periods. Using tools such as the Cornell Lab’s BirdCast, which forecasts bird migrations in real-time, communities can run “lights out" warnings on nights when large migratory movements are expected over a city, providing birds safer passage along migration routes.
There are many ways to contribute to the Lights Out solution:
- Turn off exterior decorative lighting
- Extinguish flood-lights
- Substitute strobe lighting wherever possible
- Dim or extinguish lobby/atrium lighting
- Turn off interior lighting especially on higher stories
- Close shades or blinds
- Down-shield exterior lighting to eliminate horizontal glare and light directed upward
- Utilize motion sensors on lights
- Put lights on timers
- When converting to new lighting, assess quality and quantity of light needed to avoid over-lighting with new, brighter technology
People can benefit from Lights Out too:
- Save money
- Reduce energy usage; be more eco-friendly
- Follow sustainability guidelines (for corporate structures)
- Enjoy the stars!
Resources
Lights Out Form Letter to Elected Official
Lights Out Form Letter to Building Manager
International Dark-Sky Initiative
Reducing Bird Collisions in Your Backyard
Now it’s YOUR turn to shed light on bird activity, migration, nesting, observations, and adventures in your part of the flyway!
