Building Collisions Are Killing as Many as 1 Billion Birds a Year in the U.S., Study Finds

Less than half of injured or stunned birds survive collisions with windows, new research has found, which means as many as one billion birds may be killed each year from flying into buildings in the United States.

The discovery was made by a team of ornithologists with the NYC Bird Alliance, the Fordham University Graduate School of Arts and Sciences and the Max Planck Institute for Geoanthropology.

“Even common avian species in North America are declining, so identifying and addressing threats to bird populations is critical for the conservation of not only individual species, but the ecosystems they belong to. Collisions with buildings are a leading anthropogenic cause of death for birds in the United States,” the authors wrote in the study. “Affecting over 50 avian families and hundreds of species; building collisions kill between 365 million and 1 billion birds a year in the United States alone and pose a significant threat to birds in other countries as well.”

The researchers analyzed the wildlife rehabilitation records of thousands of birds who had been involved in window collisions, reported Phys.org.

Previous research had found that windows are extremely hazardous for birds, as they are not able to see them, other than by what is reflected off their surfaces, which is often viewed as open spaces to fly into.

When birds do collide with windows it often leads to death, head injuries that can be fatal or a sometimes temporary stunning effect.

“Most studies that are published are done on birds – usually on impact – that are already dead,” said lead author of the study Ar Kornreich, a Fordham University Ph.D. student, as The Guardian reported. “The truth of the matter is there are many birds that collide and don’t immediately die.”

The research team looked at data from 3,100 cases of avian window collisions in eight states from 2016 to 2021 to come up with an estimate of how many birds are killed after surviving initial impact, reported Phys.org. They discovered that 60 percent of birds who were treated still died, mostly from brain injuries. They noted that birds commonly “wake up” following impact and fly away, seemingly uninjured.

When the researchers considered these cases, the total number of birds who died from colliding with windows in the U.S. each year rose to roughly one billion.

Preventing birds from colliding with windows is as easy as placing stickers or tape to windows and turning off lights at night.

“We cannot rely on only rehabilitation to fix this kind of problem,” Kornreich said, as Scripps News reported. “The best medicine is absolutely prevention because some of these injuries just have really bad prognosis.”

The study, “Rehabilitation outcomes of bird-building collision victims in the Northeastern United States,” was published in the journal PLOS One.