Type “bird collisions” into your computer’s search engine and the first report you may read, from the American Bird Conservancy, is that crashes into glass windows kill between 500 million and 1 billion birds per year, the majority of them windows on homes.
Other sites such as the Audubon Society report similar findings. For anyone who cares about birds and the natural world, that’s sobering.
But a groundbreaking study published this month by Stephen Hager, a professor of biology at Augustana College in Rock Island, disputes those high numbers.
His research indicates that bird-window collisions are not as widespread as the literature indicates and that they are concentrated in high-risk areas where a lot of glass is coupled with a bird-friendly habitat.
Hager began the research about 10 years ago when he noticed a bird crash into one of the big glass windows of the Augustana science building. When he went to look, he saw that the bird had died.
That led to a small study, which, sure enough, showed that 55 birds died in collisions with windows in the Hanson Hall of Science, a structure with lots of glass surrounded by bird-friendly habitat — a lot of trees and shrubs.
But is it correct to say that because 55 birds died in collisions with the science building windows that a similar number of birds collide and die by flying into windows of different kinds of buildings with different kinds of surroundings, that collisions are relatively constant and wide-ranging?
Not without further study, Hager said.
To set up his research, he used a computer program to randomly select 20 points across Moline and Rock Island.
He then identified buildings corresponding to those points and, wearing a hat with the “Augie” name on it and carrying a clipboard, he knocked on their doors, asking the owners whether he could study their buildings. He explained that he and his helpers wanted to walk around the perimeter of their buildings for a year to check for dead birds.
“It was very awkward at first,” he said. “They thought they were on ‘Candid Camera.’ ” But after Hager explained his goal, most agreed and the only two who declined were replaced by the owners of the next-closest buildings.
Then, beginning in January 2010, Hager and his helpers began systematically scouting the buildings for bird carcasses, visiting each location 21 times during each season of the year — winter, spring, summer and fall — a total of 84 visits to each of the 20 buildings.
The result? “We didn’t find hardly anything,” Hager said. “In 1,700 surveys, we found 34 birds, none around houses.”
His conclusion is that collision deaths can be attributed to two main factors: a large amount of window area surrounded by good bird habitat.
Few windows in good habitat and a lot of windows in bad habitat (concrete or other impervious surfaces) did not produce dead birds, he said.
So his recommendation for reducing bird deaths is that “we focus on problem buildings and leave the others alone.”
Architects, for example, should be encouraged to find ways to reduce vast expanses of glass while still making buildings aesthetically pleasing, he said.
Most, if not all, of the references to high bird mortality in window collisions — those found on the websites of the American Bird Conservancy and the Audubon Society, for example — are based on 40 years of research and writing by one researcher, Daniel Klem, a biologist at Muhlenberg College in Pennsylvania.
Hager’s contention is that Klem looked at too few buildings — buildings that happened to have a lot of fatal collisions — and then concluded without further study that the same number of collisions happen at buildings everywhere.
Informed of Hager’s research, Klem said he stands by his work.
“My lowest estimate (of bird deaths) would fit in his (Hager’s) findings, he said.
“Every building has the potential to kill one bird, not that it does. ... This (Hager’s research) advances the knowledge of why some buildings are more lethal than others.”