“Building Collisions” and birds in Colorado

Building collision” is a problem for birds, but not the biggest problem for migrating birds in Colorado.

The big problem: “navigational disruption” of migrating birds means that many birds aren’t able to find their desired nesting place. 80% of migratory birds travel at night, and our artificial lights are a problem. There are three reasons that research indicates that artificial lights are a problem for migrating birds. First, research shows that “skyglow on the horizon” causes migrating birds to veer toward cities. Second, research shows that birds use the stars to navigate and our artificial lights make it hard to see the stars. And finally, research shows that individual unshielded artificial lights cause migrating birds to circle and become unable to find their way.

Denver Audubon volunteers have been collecting data on dead birds found at the base of Denver buildings for several years. The results show that hundreds of birds per year die after colliding with a building in Denver. But many of these collisions may happen during the daytime, and many are resident birds, not migrating birds. By contrast, research indicates that around 60 million migrating birds have been lost in North America each year during the last 50 years. If Denver’s number is as high as 600 migrating birds colliding with buildings per year (that’s a high estimate), that would be about 0.001% of the total migratory bird population decline for North America. 600 birds dying is bad, but it’s not a significant part of the larger problem.

Furthermore, migrating birds fly, on average, over 1000 feet above ground. Few human structures exist at that altitude. The tallest building in Denver is 717 feet. Building collisions in Denver affect birds that are either (a) not migrating, or (b) at the beginning or ending of their night’s journey. Building collisions are a problem, but not the biggest problem.

Data on building collisions in Denver show that most collisions occur on buildings that are near a migratory “stopover” place, where birds rest, eat, and prepare for another night’s flight. For example, one of the worst places for building collisions in Denver is the Denver Museum of Nature and Science, on the edge of City Park, which is about a square mile in size, and a known migratory bird stopover place. It’s not the building’s size that’s the problem (it’s about four stories high), but the location. The “skyglow” of Denver draws in many more migrating birds than would otherwise travel through Denver, and many stop to rest at City Park. But again, it’s only a tiny fraction of the larger problem.

The Denver Museum of Nature and Science has one of the worst bird collision problems in Denver.

Colorado is not the same as Texas, which has a larger “building collision” problem. Colorado has fewer big cities, and many fewer migrating birds (tens of millions of birds per night rather than hundreds of millions of birds per night). Colorado does not have a Gulf Coast. Many millions of birds migrate across the Gulf each year, landing on the Texas Gulf Coast. Some of the worst building collisions recorded have happened on rainy mornings on the Gulf Coast, when tired migrating birds are coming in for a landing after a long night of flying over the ocean. They are coming in low, looking for a landing spot. They are tired, and visibility is bad. Sometimes, hundreds of birds are attracted to a single artificially-lit building, and die. Colorado does not have this issue.

Lights Out Texas is an amazing program and doing great work. Their top focus on “building collisions” seems appropriate for Texas. But the “navigational disruption” piece is significant, too. By darkening the buildings of their largest cities, they are also reducing the “skyglow on the horizon” that draws huge numbers of birds into cities, hence the Lights Out Texas approach is working on the “navigational disruption” problem, too.

But focusing on “building collisions” in Colorado is missing the larger issue. Such a focus sends the wrong message: that this is a problem only in downtown Denver, for a few dozen building managers to be concerned about.

We must act now. Research indicates that the decline in migratory birds in North America is dire, and accelerating, and that our artificial lights are among the worst problems. Research indicates that light pollution is getting worse very quickly. If we fail to act this year, there may be few birds left in North America soon.

Lights Out Colorado logo

Lights Out Colorado focuses on the “navigational disruption” problem. It’s a problem everywhere in Colorado that there are humans. It’s a problem for all Coloradans, not just for building managers in Denver. The biggest action we must take: shield all artificial lights. Everywhere in the state. Lights on people’s homes, streetlights, everywhere. It’s a big task, but we can do it, and we must.

Every unshielded artificial light, wherever mounted, causes a problem for migratory birds. From their vantage point 2000 feet above the ground, it doesn’t matter whether the light is mounted at ground level or 100 feet up. Shielding on our lights is essential for migrating birds (and good for humans, too). With shielding, birds no longer see a super-bright “star” on the ground, but only the dimmer glow of the pool of light on the ground below the light.

Birds’ eye view, thousands of feet over northeastern Colorado, looking west toward Fort Collins. Even on this clear night, the artificial lights are much brighter than the stars.

From the birds’ perspective, thousands of feet above ground, the problem is clear: the lights on the ground, even miles away, are much brighter than the stars that the birds need to find their way. In the photo, every artificial light you can see is not shielded. And the problem occurs throughout Colorado, not just this lightly-populated location in northeastern Colorado.

Please talk to your elected officials about what our local and state governments can do. See the Lights Out Colorado website for images to share on social media, information on how to talk to elected officials, and more.

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