Our buildings kill birds. What can Coloradans do about it?
share
DENVER — Approximately one billion birds die every year in the U.S. from collisions into buildings. Collisions peak during spring and fall migrations when artificial light from cities lures birds off-route.
Ahead of this year’s spring migration — which typically lasts from mid-March through early June — Rocky Mountain PBS spoke with Vicki Vargas-Madrid and Liam Price, who run Lights Out Denver, to learn more about the problem and what Denverites can do.
Since 2018, Lights Out Denver has monitored bird deaths in downtown Denver and consulted with building owners and residents to make their properties less threatening to migrating birds.
Why do bird collisions happen?
Light pollution from cities like Denver is a major factor in bird collisions, said Liam Price, a wildlife technician with Denver Parks and Recreation.
“Artificial light at night blocks a lot of celestial clues,” birds use to navigate, he said.
“They're being drawn off a migratory route that they've been flying for the past month, and that waste of energy from being pulled off their route disorients them. It makes them vulnerable to predators. It makes them more likely to collide with windows,” he said.
Once birds find themselves in a dense urban area, it can be difficult for them to get back on their migratory track.
What factors contribute to bird collisions?
Artificial light, glass and vegetation are the biggest factors, Vargas-Madrid and Price said.
Trees planted near buildings can cause reflections that disorient birds.
“We know what a window is. But they just see the vegetation behind it,” said Price.
When do collisions peak?
Although bird-building collisions happen year-round, the risk is greatest during spring and fall migration periods.Lights Out Denver relies on migration forecasts from BirdCast, a collaborative research project from Colorado State University and the Cornell Lab of Ornithology, to determine its monitoring schedule.
Price said he checks the website every day.
“Right now, we are seeing birds start to move, especially on the coastal flyways, but not a lot is going on in the Central Flyway yet,” he said.
This season, Lights Out Denver volunteers will begin monitoring April 7. Spring monitoring will last until June, when migration subsides.
How does Lights Out Denver monitor bird collisions?
Lights Out Denver relies on a team of roughly 30 volunteers who conduct monitoring walks during migration season. When volunteers find a dead bird, they document the species, its condition and location.
“We have a route in the middle of downtown Denver. It's a little over a mile and a half,” said Price.
The route centers around the Central Business District and North Capitol Hill.
Ideally, Lights Out Denver would have enough volunteers to fill shifts daily, but Price said that many of their shifts go unfilled. Roughly 10 volunteers do the bulk of the monitoring, said Vargas-Madrid.
Volunteers arrive around 6 a.m. before sanitation crews clean up dead birds.
What species are affected?
“A lot of what we see here are sparrows and smaller birds, like hummingbirds,” said Price.
While migratory birds may be at the greatest risk, volunteers regularly find non-migrating species too.
“[Artificial light will] also just affect pigeons flying from Lakewood into Denver. And it'll throw them off and kind of draw them down in,” said Price.
Two years ago, volunteers found a Great Horned Owl that had collided with a building.
Although migratory birds that navigate at night are most susceptible to the effects of urban-light pollution, non-migrating species like pigeons can also be affected. Video courtesy Storyblocks
Where do collisions happen?
Vargas-Madrid and Price declined to name specific buildings they suspect are responsible for the greatest number of bird deaths in Denver. Their monitoring centers around 17th, 18th and 19th streets near Broadway because of the prevalence of buildings built with glass.
“Studies show that most collisions happen in the lower four stories. So if there's ever buildings that have 80, 90% of those four stories that are glass…those are hotspots where we try to direct volunteers,” said Price.
While light pollution from office buildings and glass skyscrapers can be problematic, Price said that, “Statistically, residential buildings, homes kill more birds per year than skyscrapers do.”
What happens to birds that survive?
Not all birds that collide with buildings die. According to the Bird Alliance of Oregon, 54-76 percent of collisions are fatal.Vargas-Madrid said that some birds that volunteers find alive eventually succumb to trauma-related injuries.
When possible, Lights Out Denver attempts to rehabilitate birds by working with rehabilitation centers, like Rocky Mountain Wildlife Alliance.
What’s the biggest challenge to changing people’s behavior?
Vargas-Madrid said that monitoring is the first step to making change.
“I've spoken to these building owners to ask them to turn their lights off during migration seasons, their first question is, well, how do you know my building is killing birds,” she said.
Another problem is getting in contact with building managers who have the authority to turn lights off at night.
So far, Vargas-Madrid estimates that she’s talked with five building managers. While managers have been receptive, she said nothing has changed.
What can people do to prevent bird collisions at home?
For individuals who want to make their homes or apartments less threatening to migratory birds, the easiest thing to do is turn off lights, especially between 12 a.m. and 6 a.m.
“If it were all dark they wouldn't be flying towards those windows,” Price said.
He refers people to guidance from the International Dark Sky Association to “Turn off unnecessary lights, keep indoor light indoors, install motion sensors and timers to control light so it’s turned off when not needed, and shield exterior lights down so they don’t spill beyond where they are needed.”
In addition to evaluating nighttime lighting, people can install window decals, tempera paint or parachute cord to help birds see that glass is there.
Lastly, Vargas-Madrid recommends that people keep cats inside when possible. Every year domestic cats kill 1.3-4 billion birds in the U.S.
Type of story: Explainer
Provides context or background, definition and detail on a specific topic.
Provides context or background, definition and detail on a specific topic.
To read more about why you can trust the journalism of Rocky Mountain PBS, please visit our editorial standards and practices page.