U.S. Bank Stadium has long drawn the ire of bird lovers who see its huge glass walls as a deathtrap for birds. The animal rights organization PETA this week claimed birds were “dying en masse,” colliding into the stadium glass at a rate of 500 a year.
Now, though, a two-year, $300,000 bird collision study has put a data-driven number to the death toll — 111 dead birds a year, ranking the Minnesota Vikings home as medium-high in the spectrum of bird-killing buildings.
Scientific studies suggest most urban, glass covered buildings across the country kill up to about 77 birds a year, said Scott Loss, an Oklahoma State University natural resources professor who worked on the U.S. Bank Stadium study.
This new study looked at 21 buildings in the Twin Cities. The stadium was the third most lethal to birds. The worst — an undisclosed high-rise office building — killed roughly twice as many.
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“Anyone who has studied this sort of thing knew we were going to see a lot of bird collisions,” Loss said. “These are big buildings with a lot of glass.”
The surprise came in discovering the kinds of birds hitting that glass.
“In a city, you’d expect to see city birds, like pigeons or house sparrows,” he said. “What we saw instead were long distance, neotropical migrants.”
Birds like the migratory warbler and ruby-throated hummingbird, which breed in northern Minnesota and winter in South America, and often pass through the Twin Cities at night. Loss said they see the lights of a game at U.S. Banks Stadium, and get confused.
“Lighting appears to disorient birds,” he said, “and potentially draw them nearer to buildings.”
The study produced another surprising result. More birds flew into windows in areas near green spaces and city parks. Loss said trees draw birds closer to buildings. And the greenery can be reflected in the glass.
A bird might think it’s flying in for a landing on a tree branch. Instead it smacks into a sheet of glass and ends up a statistic in Loss’s study.
“Green spaces are so healthy for people,” Loss said. “But it looks like they’re not for birds. I wouldn’t necessarily suggest removing trees from around the stadium, but I wouldn’t add more.”
The study was funded by the Minnesota Sports Facilities Authority, and the Vikings. The groups put out a joint statement saying they’re “evaluating mitigation recommendations.”
The stadium is already following lighting guidelines laid out by the Audubon Society, but plans to crack down harder during times of heavy bird migration.
The statement also mentions possible glass treatments that could make the surface more visible to birds.
Loss says the other 20 Twin Cities buildings in his study were not named, but that information could be released at some point in the future.