November 15, 2012
The body of a bird killed in a window strike. Birds mistake the reflective glass as a clear flight path, flying into the window at full speed. Photo by: Paige Shoemaker.
Undergraduate biology students at the University of Alberta, supervised by biologist Erin Bayne, surveyed 1,750 local residents in person and through social media. The recruited citizens provided the number of fatal bird strikes at their homes during the previous year. By extrapolating from these local reports, the researchers calculated the collision rates for different types of homes and then estimated the national bird mortality rate. The study did not include bird strikes on skyscrapers or commercial buildings.
"Most houses have had zero collisions in the last year, but others had many more," Bayne told mongabay.com. Rural houses with bird feeders and lots of vegetation generally had more bird fatalities—as many as 43 in a year.
Bird silhouette adhered to a window. Using stickers or objects to break up a window’s reflection can help prevent bird deaths. Photo by: Sharat Ganapati.
Common birds, like sparrows, robins and chickadees, accounted for most casualties. Bayne’s study found no endangered birds killed by windows, but he mentioned that for an endangered species, "even a few collisions could have a big impact."
"This is not just an Albertan issue or a Canadian issue," Bayne said. "This is an important issue in countries around the world." In the United States, for example, an estimated 100 million to 1 billion birds die each year by crashing into windows.
Previous bird-window mortality estimates looked at fewer homes and didn’t include factors that can make some houses deadlier than others. Biologist Scott Loss of the Smithsonian Migratory Bird Center in Washington, D.C., said Bayne’s methods are a big improvement.
"Using the fact that different buildings have different collision rates is much better than trying to generalize one collision rate for all buildings," said Loss in an interview with mongabay.com. "In terms of scale, this study sets a good new precedent for other studies to try to achieve."
Bayne admits his method isn’t perfect; homeowners won't remember every bird collision over the course of a year. His group is developing an online database where residents can report incidents as they happen. However, Bayne said, the exact tally isn’t what’s most important.
"It’s a very large number regardless of how you estimate it," he said. "The question is, do we need to get better numbers to convince people that this is an issue, or do we need to start doing something about it?"
For homeowners looking to prevent traumatic bird deaths, the easiest step is to move bird gathering spots, like feeders and birdbaths, farther away from windows. The dark silhouette of a hawk, owl or falcon works well as a window covering—not because it mimics a predator, but because it breaks up the smooth reflection of the glass. Placing stickers or plastic wrap on the outside of the window also can prevent a bird from perceiving a clear flight path.
"People need to really think about what's best for the birds and not just what's best for them viewing the birds," Bayne said.
The imprint of a pigeon on a window. Common birds made up the bulk of window fatalities in a recent Canadian study. Photo by: Gary Huston.
CITATION: Bayne, EM, Scobie, CA, and Rawson-Clark, M. (2012) Factors influencing the annual risk of bird–window collisions at residential structures in Alberta, Canada. Wildlife Research 39(7) 583-592 http://www.publish.csiro.au/nid/144/paper/WR11179.htm
Thomas Sumner is a graduate student in the Science Communication Program at the University of California, Santa Cruz.
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