There are thought to be 20 billion birds in the Lower 48 states. Their lives are precarious. Some species suffer “a constant risk of death from early adult life to the end,” according to one classic study. Another puts the chances of early death for adult songbirds at 70 percent. Altogether, 5 billion birds die in the United States every year, from natural forces and from human interference.
Pesticides kill 72 million birds directly and many more over time. Power lines, communication towers, motor vehicles, wind turbines and bi-catch fishing operations take a big toll. Tree-cutting, swamp-draining and other habitat destruction is thought to be the biggest killer. Slaughterhouses kill 25 million chickens and turkeys. Cats, both domestic and feral, kill several times that many birds, more than a billion per year, by some estimates.
Buildings kill birds, too. Collisions with windows and other structural features are thought to kill 600 million birds each year. Homes and other small and mid-rise buildings cause nearly all of those deaths, with office towers accounting for fewer than 1 percent. Buildings in downtown Minneapolis are believed to kill birds at a rate of at least 1,000 per year, or 2.7 per day. Altogether, fewer than 3 percent of the U.S. bird population dies each year from collisions with buildings.
Because of obvious difficulty gathering data, scientists lack absolute confidence in these numbers. Still, they represent best estimates based on modeling and extrapolation. They are offered here in hopes of bringing badly needed perspective to an overly emotional debate about the design of the Vikings stadium now rising in downtown Minneapolis.
Bird enthusiasts are late to the game. They now insist that clear glass, the stadium’s signature architectural feature, be replaced by fritted glass, a cloudier version that’s thought to be safer for birds. The Minnesota Sports Facilities Authority, the owner and builder of the stadium, has committed to a lights-out program that will darken the building — inside and out — as a way to reduce chances of nighttime bird collisions. It also will carefully monitor its property for bird collisions once the stadium opens in 2016. But it will not replace the clear glass.
Given the numbers cited above, that’s a reasonable response. The addition of one glassy building in Minneapolis won’t appreciably alter the mortality rate of the North American bird population. As the numbers suggest, it wouldn’t be unusual for birds to occasionally strike the building. But those collisions would barely register on a very long list of ways in which humans routinely interfere with nature.
This sounds callous, but individual bird deaths from collisions are almost meaningless as long as bird populations remain constant. To say it another way, a bird escaping death by collision is almost sure to die soon from something else, whether storm, poison, starvation or some other danger. “People keeping their cats indoors would have a far greater impact on bird survival than whatever happens with the stadium,” said University of Minnesota ornithology Prof. Robert Zink.
Truth is, no one knows how the stadium’s design will interact with birds along the Mississippi Flyway until it’s up and running. To single it out as a “cathedral to bird killing,” as some critics have already done, is hyperbolic.
The sports authority’s point about keeping the clear glass isn’t about the $1.2 million it would take to replace it. It’s about a promise made to Minnesotans — and especially to neighbors in Downtown East — that the new stadium would not be an ugly blight on the cityscape, as the Metrodome clearly was.
Architects promised a building that would be as transparent as possible. Yes, it would be big, but expanses of glass would help mitigate its mass. To avoid the cost and unsightliness of a retractable roof, a translucent polymer top would allow spectators to see the sun and clouds above. And its signature feature, a wall of glass with huge pivot doors opening to a plaza and affording a clear skyline view, would add to the feeling of being outdoors. Substituting bird-proof glass would remove that illusion, designers say, while making the stadium’s exterior more monolithic.
The dispute comes down to competing values: architectural aesthetics vs. large-scale bird collisions that may or may not happen. It may also come down to a court challenge. One of several bird groups, the Minnesota Legal Defense Fund for Migratory Birds, contends that the stadium design violates the Endangered Species Act and a number of other federal and state laws. The group intends to seek a court injunction to stop glass installation until the matter is settled. A key argument is that the entire flyway — not just nesting and breeding grounds — should be considered protected habitat.
If, in 2016, whole flocks of migrating birds begin striking the building, then obviously the sports authority would be forced to change its tune. For now, it’s wise for the authority to continue searching for glass products that might deter birds without damaging the stadium’s design. If such a product is found, contingency funds are available to install it. Still, the broader picture is worth considering: When controversial buildings are involved, bird collisions make for high drama. But they don’t amount to much in the larger scheme of things.