Football and dead birds seem to go together. Super Bowl Sunday brings an enormous bump in chicken wing sales, and for many Americans, digesting Thanksgiving turkey doesn’t seem right without a little gridiron action. The Minnesota Vikings, however, are preparing to offer a much less festive threat to our feathered friends: a new stadium featuring 200,000 square feet of glass, situated on a major bird migration route. Audubon Minnesota is calling it a “death trap.”
According to the nonprofit state group, several features of the Vikings’ $1 billion stadium, set to open in 2016, would endanger migrating birds. The Mississippi River, which flows only a few blocks from the stadium site, is a major thoroughfare for wildlife. With one-half of North American bird species traveling along the river’s path over the course of the year, the National Park Service says the Mississippi “forms the core of one of North America’s great flyways.”
The threat to those birds, Audubon says, is twofold: lights and glass. Lots of lights and lots of glass.
To start with, cloudy weather can force migrating birds to fly lower than they usually do. When this happens at night, they seem to become strongly attracted to bright lights—the kind you might see during a Monday Night Football game. Once these birds reach the light source, notes University of Minnesota ornithologist Robert Zink, they often circle it furiously for reasons unknown. Those that don’t strike the building or nearby wires can drop from exhaustion.
Glass may be even more of a problem. Each year, hundreds of millions of birds—representing more than one-quarter of American bird species—die in collisions with building glass. Multiple sides of the new stadium and half of its slanted roof would feature large walls of glass, some more than 95 feet tall.
Back before World War II, when there was far less plate glass in American architecture, observers chalked the occasional bird-building collision up to the psychological shortcomings of a few clumsy individuals. As the video below suggests, those humans may have just been projecting their own limitations onto the birds.
We now know that bird-glass impacts are not the result of absentmindedness. Certain architectural and landscape features make buildings dangerous to a wide variety of bird species, and many organizations offer bird-safe building guidelines. Large expanses of glass that reflect outside vegetation, for instance, are dangerous to birds, and placing large shrubbery within glassed-in lobbies is also inadvisable. The recent advent of ultra-clear glass, which has low levels of iron and transmits 10 percent more light than standard glass, has compounded the problem.
It’s still not always clear which buildings will be bird killers, though. Between 2007 and 2009, volunteers from Minnesota’s Project Birdsafe collected bird carcasses near 120 buildings in Minneapolis and St. Paul. Five of those buildings were particularly lethal, accounting for almost half of the 1,400 birds collected. Glass and vegetation alone couldn’t explain why.
“We know there are some factors that draw birds to buildings, but we don’t know all of them,” says Robert Zink, who helped direct the project.
Zink, for his part, doesn’t think buildings represent an existential threat to birds. Having tracked bird population trends for decades, he found no correlation between a species’ population trend and tendency to collide with buildings. Although some birds, such as warblers and sparrows, tend to have more fatal building strikes than others, Zink says we have no evidence that a species is threatened by collisions.
“I hate to be cynical, but so what?” he asks. “People might get excited when we find 200 dead white-throated sparrows, but those are extremely common birds.”
Matthew Anderson, executive director of Audubon Minnesota, argues that the research is inconclusive, and we ought to err on the side of protection.
“No one knows for sure whether collisions are having population effects, because we’re not running longitudinal studies,” he says. “Decades ago, we didn’t have massive downtowns with walls of glass along migratory flyways.”
Whether we have an absence of evidence or evidence of absence is an important distinction, because companies like the Vikings are hesitant to spend money on bird-safe modifications unless they know it has a conservation impact. The team has agreed to dim the stadium’s lights on non-game nights and turn them off after midnight (which also seems like a good idea for saving money and electricity), but it has balked at the more costly changes suggested by bird lovers.
It refuses, for instance, to install fritted glass, which is speckled with small ceramic dots to make the glass visible to birds. The Dallas Cowboys stadium, finished in 2009, features stretches of fritted glass. The upgrade to the Minnesota stadium would cost just over $1 million, a minor sum in the grand scheme of construction costs.
And we know that fritted glass works. Flight tunnel tests prove that birds are more likely to fly toward clear glass than fritted glass. When New York City’s Javits Center—which is also perched on the side of a major river—added fritting to its plain glass, bird deaths dropped substantially.
“For one-tenth of one percent of the cost of the stadium,” Anderson says, “we can do the right things for migratory birds in a building that’s going to dominate the skyline for generations.”
To him and other bird lovers, that’s money well spent. Even if it never helps win a football game.
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