Disappearing stopover habitat, more skyscrapers, stronger storms—the biannual flights for migratory birds are getting riskier. But scientists are working to make migration safer.
The Danger of Disease Outbreak
Large flock travel reduces the risk of disease even though it keeps birds safer. Large flocks are vulnerable to disease outbreaks, which can occasionally wipe out the entire flock. Even though this first loss is startling, the disease is then carried by the remaining birds to populated winter homes, where it spreads like wildfire. As a result, the number of birds that will return during the spring migration will drastically decrease.
Photo by Ke Vin on Unsplash
Light Pollution and Migration
Even though long-distance migratory birds use their stopover habitats during the day, many of them log their miles at night.
For thousands of years, birds have found that migrating at night, when there are fewer predators, more favorable winds, and cool, humid air that reduces water loss, is an effective migration strategy. An additional benefit of nocturnal migration on clear nights was that it allowed birds to use the starry sky as a navigational tool.
But within the past century, birds’ stellar view has faded. Approximately one-third of the world’s population, or E2%80%99, resides in areas where they are unable to see the Milky Way and where light pollution is expected to rise by approximately 2% annually. Rather, a new constellation system has emerged from the surface of the earth: billions of man-made lights that dim the sky above while beckoning brightly from below.
“[Birds] are being disoriented, pulled into cities, and they’re being set up for a less successful stopover,” says Kyle Horton, a collaborator on the BirdCast program who heads up the Aeroecology Lab at Colorado State University. Horton says that migratory birds drawn into urban areas by bright lights at night are being lured into a suboptimal stopover. “Cities generally have less [tree] cover and fewer native plants, which equals less food. While people may enjoy seeing migratory birds appear in urban areas, it’s probably not good for bird populations.”
Horton participated in a study with New York City Audubon a few years ago while he was a postdoctoral researcher at Cornell Lab. The study found that over a seven-night period, more than a million birds were lured into New York City by the mile-high light beams aimed skyward at the Tribute in Light, a Lower Manhattan memorial to the 9/11 victims. The beams caused the birds to circle pointlessly for hours. Horton and other scientists were also able to determine that migrating birds in the area were being drawn away from their usual routes and toward Lower Manhattan and the Tribute by analyzing weather radar data. The study provided valuable insights for a partnership with the National 9/11 Memorial.
NYC isn’t the only source of light pollution. After analyzing eBird data last year, Horton and research ecologist Frank La Sorte of Cornell Lab discovered that migratory birds are being drawn to cities across North America. Large cities’ enduring nighttime glow may be significantly changing the migratory patterns of birds.
During their migration in the spring and fall, birds are appearing more frequently than anticipated, according to Horton. “Stopping in urban areas could be changing or slowing their migration routes in ways that could have consequences for birds throughout the rest of the year, beyond the immediate danger of cars, buildings, and predators.” ”.
Based on radar and light pollution data, Chicago was determined to be the most hazardous city in America for migrating birds. Sadly, the city also possesses extremely comprehensive data on bird collisions—more than 100,000 dead birds meticulously gathered and indexed in the spring and fall over the previous 40 years.
Due to close observation at the location, about 40,000 of these dead birds have been gathered at McCormick Place, a glass-fronted convention center located in Chicago’s South Loop. Situated on the brink of Lake Michigan, this location has long attracted migratory birds along the Great Lake’s shores, providing an abundant supply of study material.
In 1978, Dave Willard, the former manager of collections at Chicago’s Field Museum of Natural History, began gathering dead birds at McCormick Place. He claims that although there are still many bird deaths there on a regular basis, the number of deaths decreased from thousands to hundreds after the building started turning off its lights at night in the early 2000s. Art by Charlie Harper.
The bird collision data from McCormick Place is extremely detailed, recording not only the window that each bird struck over time but also whether or not the lights were on in that window. Working with Willard and colleagues, Cornell postdoctoral researcher Benjamin Van Doren will soon release a study that demonstrates the importance of a single window bay for the first time. Van Doren discovered that windows surrounding an unlit window bay are marginally less likely to experience collisions, even when illuminated, in addition to a darkened window bay being significantly less likely to sustain a bird impact at night than lit windows. This indicates that birds aren’t just hitting some windows while avoiding others.
Van Doren notes that “falling birds seem to be drawn to particular light sources, rather than just confused by general city or sky glow.” Thus, darkening a single window bay is likely to reduce the number of collisions even in an otherwise well-lit area. ”.
Chicago Audubon has overseen the city’s Lights Out program since 1995, promoting the turn-off or dimmering of building lights in the Loop area in the spring and fall. However, Dave Willard believes that the city’s overall bird mortality rate may be rising as a result of all the recent construction that has occurred downtown. He believes that Van Doren’s latest findings will facilitate persuading individuals that small actions can yield significant advantages.
- The Hunt Headquarters in Dallas with its lights on. As part of the Lights Out Texas campaign, the building turned down its lights during the busiest migration period. Photo by Lloyd and Melissa Clayton.
- The Hunt Headquarters with its lights off. One of the Dallas buildings that turned off its lights in the fall of 2020 during the busiest bird migration was this one. Photos by Lloyd and Melissa Clayton.
In response to requests from Mayor Eric Johnson and former First Lady Laura Bush to turn out unnecessary lights at night, a number of downtown tenants and building owners in Dallas, Texas—another metropolis on the list of the most dangerous cities for migratory birds—took a small action last October. During the busiest days of the fall bird migration, when over a billion birds pass through Texas, the public announcements were scheduled. The PSAs in newspapers and on social media were a part of BirdCast’s new Lights Out Texas campaign, which aims to raise awareness of the advantages of darkness for migratory birds.
And they worked. Several of the most recognizable downtown structures in Dallas, including City Hall, the Dallas Zoo, and the AT Lights Out Texas is requesting that Dallas dim its lights from mid-April to early May in observance of the annual spring migration of one billion birds. Additionally, other Texas cities will receive the call this time.
Julia Wang, coordinator of Lights Out Texas, says, “We’re now talking to folks in cities all across the state who took notice of Dallas’s participation last fall.” “We know Texas is crucial for migratory birds, so having widespread support there would be a huge boost for the movement nationwide.” ”.
The Dangers of Lack of Experience
Many young birds migrate in the fall, and these are dangerous and difficult journeys. Many young birds do not make it through their first migration if they do not receive guidance from seasoned adult birds. Juvenile birds will not survive if they cannot locate food sources or if they get lost and deviate from the path. Backyard birdwatchers frequently see a stray young bird at their feeder without realizing that the bird is probably lost.
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