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Sandhill cranes return to the Monte Vista National Wildlife Refuge in 2021. (John McEvoy, Special to The Colorado Sun)

While you slept over the weekend, an estimated 9.5 million birds took to Colorado’s sky. During the peak of this spring songbird migration period, over 350 million birds fly over the continent each night, pursuing the rush of tasty bugs and warm weather that comes with spring, the resources and conditions necessary to raise their young.

The Aeroecology Lab at Colorado State University, in collaboration with Cornell Lab of Ornithology, forecasts the intensity of bird migration using two decades of historical radar data linked with meteorological data (think: wind speed, direction, barometric pressure) to help people make choices that can ease some pressure on birds as they make this taxing twice-a-year journey.

At least 100 species of birds will eventually pass through or settle in Colorado, says Kyle Horton, principal investigator at CSU Aeroeco Lab and associate professor. We’re talking warblers, sparrows, swallows, hummingbirds, shorebirds, waterfowl and more. 

Researchers like Horton want to better understand how organisms, like birds and bats, use the lower atmosphere, and how they interact with humans and all that we do. Lighting up the night sky and building across natural landscapes impacts birds, especially during migration, and scientists hope to support healthy bird populations and the ecosystem services they contribute, such as pollination and insect control.  

Birds generally move north in the spring, but with such diversity of species, migratory patterns vary. For some, Colorado might be as far south as they range during the winter. Other birds winter farther south, in Mexico or South America, and are just passing through.

Whether temporarily overhead or resident species tucking in for the season, these birds face challenges brought on by human activity. Bird populations, particularly migratory birds, are threatened globally by habitat loss due to land clearing or converting forests to some other cover type. 

Cat predation is a significant threat for birds, with billions lost annually to feral and domestic cats. There’s also the risk of colliding with structures, as they don’t perceive reflective building windows or tall structures the way we do. 

Horton says light pollution adds a relatively new layer of threat to migratory birds. Migration is a dangerous behavior to begin with, and light pollution increases long- and short-term risks by luring them into potentially disorienting, resource-scarce or hostile habitats. 

Most migrating birds fly at night, and can be attracted to a light source and fly into an urban area, where their risk for collisions or being killed by predators increases. But even if they evade immediate dangers, it might take them longer to find enough food in an urban area, delaying their arrival to the final destination, which can impair breeding or reduce the number of their offspring. 

Light pollution of any kind can be an issue, and researchers are just starting to look at the differences in urban, rural, and open space light pollution. So far, it seems like more lights in a bright, urban area mean more misguided birds.

With that, Horton says the urban sprawl happening across Colorado “is likely going to be a detriment to migratory birds and their ability to successfully navigate north and south in the spring and fall.”

Though there isn’t empirical data to support this, Horton thinks a single, really bright light source in the countryside could be problematic, too, as the contrast to surrounding darkness “might serve as a really dominant stimulus to these birds.”

Horton and researchers across the country studied some impacts of bright light sources on birds, using the Tribute in Light art installation’s two columns of light beaming into the sky at the September 11 Memorial and Museum in New York City. Over the course of seven nights of illumination from 2008 to 2016, they estimated that 1.1 million birds’ migratory patterns were interrupted to move through the lights.

Colorado can address and minimize light pollution by turning off the lights. Literally. 

Horton and CSU Aeroeco Lab are trying to take the science in the direction of conservation action. They post “lights out” alerts to notify the public, like building managers and folks who have the ability to turn off their lights at night, so they at least know when there is a big night of migration coming up. 

An example of CSU’s Aeroeco Lab’s migration forecast, for May 20. (Screenshot)

While scientists and advocates might hope that lights could be turned off throughout migration periods, Horton knows they won’t get much traction telling everyone to hit the lights for 100 nights. But if they can encourage others to turn off lights for 10 crucial nights in the spring and fall using migration forecasting, it could make a big difference.

This logic applies to other threats as well. Horton noted that collisions with wind turbines are a pressing topic that requires nuance, and although the threat turbine collisions pose is “pretty low” relative to other pressures like habitat loss, cat predation and climate change, using predictive forecasting to potentially hold off on wind energy production on nights with 50% of birds passing over the area is a worthwhile compromise. 

Lights Out Colorado is a voluntary program that aims to minimize light pollution. It was developed by The National Audubon Society, the International Dark-Sky Association, and Denver Audubon. It encourages people to shut off, shield, or alter their lighting during bird migration seasons — April and May, and August and September — with the hope of saving millions of migrating birds.

More than 300 people across 36 Colorado counties pledged their support, a response that Zach Hutchinson, community science coordinator at Audubon Rockies and co-organizer of Lights Out Colorado, called “amazing.”

“We are not in every community, but we need to be shutting out lights in every community and so, [we’re] asking people to just be active, with their local governments, their local agencies, their local business owners, to approach them about better ways to discourage skyglow.”

In the short term, Lights Out Colorado is asking everyone to shut off outdoor lights when it is safe to do so and block out indoor lights at night. If that’s not an option, there are other ways to prevent skyglow, including shielding the lights and focusing them downward, which is where the light is needed, anyway. 

“We can start to make a big impact just by making those simple changes,” Hutchinson said.

A ruby throated hummingbird approaches a feeder in Idledale on May 5, 2020. (Andy Colwell, Special to The Colorado Sun)

Healthy bird populations and migrations are important, Horton says, because birds provide many services to Colorado, both ecologically and economically.

By eating massive amounts of insects, birds remove some pests, like mosquitos, from the landscape. Horton says birds like martins or swallows can be beneficial to have around. 

Some birds, like hummingbirds, are pollinators and help with agriculture and flora across the landscape.

Hutchinson says bird populations can tell us about the health of ecosystems that we depend on, too. In grasslands, if bird populations are struggling, it can be an indication of the quality of the range land, whether concerning grazing animals or growing crops.

Birds offer another benefit, too, for those who keep an eye out for them. Bird watching is a popular pastime for many people. In 2016, 45.1 million people observed birds around their homes and on trips, according to the 2016 National Survey of Fishing, Hunting, and Wildlife-Associated Recreation

A demographic and economic analysis of birding from 2011 showed that 85% of the approximately 1.2 million birders age 16 and older in Colorado were state residents. A study for Colorado Parks and Wildlife reported that wildlife watching contributed $2.4 billion dollars in economic output per year in Colorado. 

The pandemic has bolstered bird watching among Coloradans. There was a 33% increase in birding checklists submitted during the Great Backyard Bird Count Feb. 12-15 this year in Colorado, Kate Hogan, Denver Audubon’s community outreach coordinator, told  Westword

Special to The Colorado Sun