Lights Out Denver

Lights Out Denver (LOD) is an initiative of Denver Parks and Recreation. Part of Denver’s commitment as an Urban Bird Treaty City, the program aims to increase awareness of migratory bird collisions with buildings in the City and County of Denver, and to promote practices that can help prevent these needless deaths. This program collects data on bird strikes in downtown Denver during spring and fall migration to identify threats to migratory birds and to demonstrate the necessity of bird-friendly building regulations. LOD also provides information on how individuals, businesses, property owners and managers can help reduce migratory bird deaths. Our goal is to help local businesses save energy, money, and migratory birds by promoting bird-safe building designs and reducing nighttime lighting! 

Bird migration in Denver

Denver is along a principal route of the Central Flyway, which birds use to make their annual journey from breeding grounds in the north to wintering grounds in the south. Denver provides a wide range of habitat for more than 300 bird species that migrate through or nest in the city. While exact timing varies year to year, spring migration generally occurs from mid-March to the beginning of June and fall migration occurs from mid-August to the beginning of November.

Diagram of North American Migration Flyways with principal routes for migrating birds

In addition to contributing greatly to our experience of nature, birds play an essential role in our urban ecosystem. For example, birds:

  • Consume billions of insects daily (including mosquitos)
  • Pollinate plants
  • Disperse countless seeds

Birds also contribute to our economy, as birdwatching has become the second most popular leisure activity in North America, after gardening.

How are buildings a threat to migratory birds?

Building collisions are a leading cause of bird fatality during migration in North America, with the American Bird Conservancy estimating that up to one billion birds die each year in the United States from building collisions.

Why do window strikes happen?

  • Birds cannot see glass, they can only see what the glass reflects.
  • Glass often reflects open sky, trees, and other vegetation that is desirable to the birds. Collisions occur when birds attempt to access this reflected habitat and fly into the glass.

Why is nighttime lighting a problem?

  • Birds are attracted to artificial lights at night, drawing them into light-polluted city centers and increasing their chances of encountering and striking a building.
  • This problem is amplified during spring and fall migration, as most of our native birds migrate at night.
  • Nocturnal migrators use the moon and stars to aid in navigation and become disoriented by artificial lights at night. Birds may confuse building lights for stars and fly in circles around the buildings and die of exhaustion or collide with the windows.

What factors make buildings unsafe for birds?

  • Windows: More glass leads to more strikes!   As the percentage of window surface on a building increases, so does the risk of avian mortality.
  • Height: Buildings do not have to be tall to be a threat to birds! Most collisions occur in the first 3 floors of a building. While tall buildings kill more birds per building, individual residences kill more birds cumulatively.
  • Vegetation: Landscaping near building windows attracts birds! Trees reflected in windows and potted plants inside windows confuse birds and increase the chance of a collision.

How can we reduce building collisions?

  • Turn off lights at night
  • Move vegetation away from windows
  • Install bird-friendly decals on windows to help birds perceive glass as a barrier
  • Create legislation and city ordinances that address bird-friendly building designs

Benefits of reducing nighttime lighting

Turning out lights yields many rewards:

  • Energy and cost savings
  • Reduced light pollution
  • Decrease in CO2 emissions
  • A safer environment for birds
  • A healthier environment for us all

While Lights Out Denver is focused on reducing nighttime lighting during key bird migration periods (April 1-May 31 & August 15-November 15), building managers are encouraged to participate year-round.

If you are interested in learning more about what your building can do to support bird conservation, contact


How can I help?

Lights Out Denver needs your help collecting data on bird collisions in downtown Denver. Join our team of citizen scientists and patrol routes, collect data, and help transport injured birds to wildlife rehabilitation centers. Your efforts are vital for this program to succeed! By monitoring for bird collisions, you can help gather the data we need to convince building owners and legislators that Denver needs to step up, and turn lights off, to protect birds.

For more information about volunteering, contact


Lights Out Denver Partners

The Lights Out Denver program could not succeed without the support of our partners. Learn more about these organizations below:

Bird Conservancy of the Rockies

Denver Audubon

Denver Museum of Nature & Science

Greenwood Wildlife Rehabilitation Center

Wild Bird Rescue & Rehab