For migratory birds, tweeting and flying could be deadly. Birds that emit high-pitch sounds midflight are putting themselves in danger, new research has found.
Worse, researchers said that the vocalizations known as flight calls during nighttime migrations might be luring other birds into their deaths.
Urban Lights Endangering Migratory Birds
Many bird species such as sparrows use high-frequency vocalizations at night to navigate their surroundings. However, previous studies found that these birds tweet more often in urban areas where there are lots of artificial lights.
Researchers wanted to investigate whether the presence of artificial lights has an impact on migratory birds traveling at night. They found that birds that produce these faint chirps are more likely to collide with buildings than those that do not.
"Nocturnal flight calls likely evolved to facilitate collective decision-making among birds during navigation, but this same social behavior may now exacerbate vulnerability to a widespread anthropogenic disturbance: artificial light from buildings," said Benjamin Winger. an evolutionary biologist at the University of Michigan and the first author of the study published in the Proceedings of the Royal Society B.
Winger and a team of scientists looked at 40 years' worth of data on bird collisions across Chicago, Illinois and one year of data on bird collisions from Cleveland, Ohio. In total, the researchers analyzed more than 70,000 records of bird collisions for the study.
They also suspected that the glare of artificial lights is disorienting migratory birds. Birds sense the magnetic field and use it as a guide to where they need to go. However, the scientists proposed that artificial lights in urban areas might be disrupting the birds' internal compass, causing them to vocalize more.
"We hypothesized that if flight calls are important social cues for decision-making during nocturnal migration, individuals from species that make flight calls may attract one another vocally when disoriented by artificial light," the authors wrote. "This relationship may spawn a vicious cycle of increased mortality rates if disoriented individuals lead other migrating individuals to sources of artificial light."
The researchers said that the species that were overrepresented in the dataset use flight calls, which means that mid-flight tweeting is a significant predictor of bird collisions. The study also linked the frequency of collision with the amount of artificial light present on a certain night.
Cities Most Dangerous For Migratory Birds
A separate study published in the journal Frontiers in Ecology and the Environment named the top 10 cities in the United States where the amount of artificial light are impacting bird migration, causing the creatures to die from building collisions.
Chicago is named as the most dangerous city for birds in both spring and fall migration. Houston and Dallas appear on the second and third spots in spring and fall lists respectively.