Bird experts cite habitat loss, predators — especially cats — and collisions with buildings, as the biggest threats to the world's bird populations.
Bird researchers say evidence shows that building design changes and window treatment can reduce some of the toll from building collisions.
Audubon Minnesota is in its fifth year of research looking into how many birds are being killed by flying into buildings and what can be done to reduce the number. In the Twin Cities, Audubon Minnesota collected 1,400 dead birds from 2007 to 2009, representing 100 different species — mostly songbirds.
Millions of birds are just winding up their spring migration, and the ones still alive have completed a harrowing trip of thousands of miles. They've come from their winter homes in the south to summer breeding grounds in the north.
Once a week, Audubon Minnesota volunteer Brian Goodspeed walks a carefully prescribed route in downtown St. Paul collecting the bodies of birds. The likely cause of death was a collision with a building.
"We're not just interested in collecting as many dead birds as we can get. What we're really trying to do is collect the information about how birds react to certain architectural types," Goodspeed said.
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Different nationwide estimates put the number of birds killed when they collide with buildings at between 100 million and 1 billion. An early strategy to try and reduce the toll was to encourage owners of tall downtown buildings to turn off lights at night. Bright night-time building lights appear to confuse migrating birds.
Amy Wimmer, general manager for the 57-story Wells Fargo Center in Minneapolis, said five years ago, the building's owner, Hines Interests, started turning out lights at night during spring and fall bird migration.
Now, Wimmer said, they're keeping the lights off at night all year.
"It really doesn't take a lot more effort for us for the lights to come off earlier, and anything we could do to help the environment, it's something that we had seen in other cities such as Chicago," Wimmer said.
Researchers say it's too early to show results from the so-called lights out program in the Twin Cities. However, University of Minnesota professor Robert Zink, curator of birds at the university's Bell Museum, said the Chicago lights-out effort reduced bird deaths by 75 percent.
Zink and Audubon Minnesota have a new plan to reduce bird collisions with buildings day or night. A lot of newer buildings are covered with glass, and Zink said many birds are simply oblivious to glass as something they can't fly through. He said buildings with large reflective glass, coupled with potted plants and shrubbery near the windows, can be especially troublesome for birds.
"Unfortunately to a bird that doesn't see glass the way we see glass, having big potted plants on one side and shrubbery on the other side is a recipe for disaster," he said.
Audubon Minnesota has a new booklet on how to make buildings safer for birds. Joanna Eckles, who helped write the book, said buildings can use etched or frosted glass to make large windows more visible to birds. There are other benefits as well.
"You can actually reduce the amount of heat coming in so you can reduce your cooling costs and birds can see the glass," Eckles said.
Twin Cities architect Edward Heinen also contributed ideas to the Audubon Minnesota booklet on bird-safe building guidelines. He said besides windows, birds can be confused by a building layout as well.
Zink and Project Bird Safe will continue to encourage architects and building owners to make design changes to reduce collisions.