The Minnesota Vikings stadium currently under construction is a gleaming structure of light and glass. Its 200,000 square feet of glass will allow those outside the stadium to see inside and will let in natural light. But this shiny cathedral for football is also expected to be a death trap for migratory birds. The Minneapolis stadium is on the Mississippi Flyway, the major migratory route for songbirds and waterfowl in the US.

The total cost of the stadium is currently $1.024 billion, half of which is public money. Arguments about bird safety began in 2012, when the design was first revealed to the public. The reaction of Sharon Stiteler, the author of 1001 Secrets Every Birder Should Know (and long-time Vikings fan) was representative of the reaction of a lot of birders I’ve talked to: “Holy crap, that's gonna kill a lot of birds.” Dr. Daniel Klem, bird safety researcher, said “You're building a bird killer."

Despite public petitions, requests from multiple prominent bird conservation organizations, and a unanimous resolution from the Minneapolis City Council, on August 22 2014 the Minnesota Sports Facility Authority (MSFA) announced their decision to not to make any changes to the glass walls of the stadium to protect birds.

The new stadium (and future Super Bowl Venue of 2018) is built on a spot that, by some estimates, 50% of North America’s migratory birds pass over during spring and fall migration. What would it cost to make the stadium safer for birds? Using ‘fritted” glass, or glass treated with a small pattern to increase visibility, would add $1.1 million to the cost of the stadium. So, for less than 0.1% of the total budget of the stadium, MSFA could avoid a huge PR fumble. (And, you know, not kill birds. )

Why would MSFA not choose to make changes to save birds? And what happens now?

Roughing the Passers

Forty percent of all North American waterfowl, and up to 50% of all migratory bird species use the Mississippi River as a navigational aid. The exact numbers are estimates, since most birds fly at night, but it's probably safe to say at least 1 billion birds pass by yearly.

Radar from May 2014 shows migrating birds heading north on the Mississippi Flyway. The blue circles are birds, not storms. BirdCast, Cornell Lab of Ornithology

Enough birds follow the Mississippi Flyway that they are picked up by radar on calm evenings. It’s not just ducks and geese; there are little songbirds like the Cerulean warbler, which breeds in Minnesota, migrates to Peru for the winter, and then returns in the spring. This trans-continental journey is fueled entirely by insects; a big Cerulean Warbler weighs just 10 grams (0.35 ounces).

Migrating birds are unprepared to deal with human structures; their vision evolved to deal with trees, not wires, cell phone towers, and skyscrapers. “Birds can’t tell the difference between an actual tree and a reflection of a tree,” said Dr. Christine Sheppard, Director of the American Bird Conservancy Bird Collisions Program.

They can’t learn context as we do, that certain shapes and structures signal glass and hard surfaces. (But don’t feel that smug; an awful lot of people have trouble seeing glass doors too.)

Light at night seems to profoundly confuse birds; it’s common for migrants to become stuck in bright searchlights. For example, the 9/11 memorial is periodically turned off to release migrant birds trapped in the twin beams of light.

The combination of lights and reflective glass is deadly for birds. Estimates of the total number of birds killed yearly by building strikes fall around the 998 million bird mark. Many cities have programs to collect and record the dead, including Minneapolis. In the Twin Cities, 131 different bird species have been collected at the base of buildings; 97% of those birds are native species. It’s not pigeons and starlings that are being killed, it's Canada Warblers and Golden-Winged Warblers, both identified as "rare or declining" Birds of Conservation Concern.

USGS Sam Droege USGS Sam Droege

Penalty Fowl

MSFA has agreed, in partnership with the Minnesota Audubon Society, to adopt guidelines consistent with Project Lights Out, a program that several large buildings in the Twin Cities participate in to reduce nighttime light during migration.

The MSFA rejected Audubon's calls to use fritted glass, or glass that is treated very subtly with patterns to reduce bird collisions. Fritted glass was initially developed for energy conservation, because it reduces glare and heat entering and exiting buildings. Since MSFA is seeking LEED sustainability certification, it was hoped they would see fritted glass as a win-win in terms of bird safety and energy. "One of the reasons we keep coming back to the fritted glass is it’s a product being made by the company that is already on contract to provide the glass for the stadium, and that is a local Minnesota company," said Matt Anderson, director of Minnesota Audubon.

A 2012 Minnesota law requires all publicly-funded buildings to meet sustainability guidelines, including LEED bird-safety criteria. Technically, the stadium is grandfathered in as an exception, since the project began just before the regulations were passed. "Technically, [MSFA] aren't required to comply with Minnesota's Bird Safety Sustainability law," said Sheppard, "but they aren't that far away from it. I can't and I would not ask people to replace glass windows with solid walls, but there are effective patterns that cover less than 8% of the glass surface."

On July 24 2014, the MSFA issued a statement:

“The design was completed prior to changes in state guidelines related to bird-safe glass. We were able to adopt operational guidelines used by other downtown office and residential buildings, we were unable to change the design and do not have the budget to include the $1.1 million needed for bird safe glass."

That statement is now viewed with skepticism, though, since on August 22 2014 , an additional $46.1 million was added to the stadium budget to cover cost over-runs and to preserve fancy amenities like escalators, and plush boxes, and a mysterious "internal system that will deliver beer kegs." On the same day, Jeff Anderson, Executive Director of Communications for the Vikings, tweeted "bird-safe glass wasn't a cost issue. Significantly affects the design and the view through the glass."

The full price of the stadium is approximately $1.024 billion. The public contribution toward the project remains at $498 million. On August 23rd, Chair Michelle Kelm-Hagen said “It’s not a cost issue, it’s a design issue,” adding that fritted glass would turn the light in the stadium “murky.”

The Dallas Cowboys Stadium was built using fritted glass for both bird safety and energy conservation reasons. Hundreds of buildings around North America use fritted glass, including museums; no issues with "murky light" have been reported.

A Ruby-throated Hummingbird found dead after striking a building. These tiny birds migrate across the Gulf of Mexico each year. Twice. USGS Sam Droege

A Different Kind of Super Collider

A steady rain of bird bodies falls silently every night around large glass buildings. Ovenbirds collide with buildings and die in fairly large numbers. There doesn’t seem to be any impact on their population, though; this species is common enough that thousands of deaths don’t seem to matter. Some species (dubbed “super-avoiders”) like swallows are nimble enough in the air they rarely hit buildings.

But little warblers and hummingbirds—our smallest birds that travel some of the greatest distances—are super colliders. They are over-represented in building kill counts. These are also the birds with the smallest populations, the most restricted feeding and habitat requirements, and the species most likely to be listed as threatened and endangered. They are already at risk, even without big human buildings in the equation.

In research papers on bird kills, the “crippling bias” that researchers discuss isn't mathematical; it's questioning when a bird should be counted as dead. Some birds collected at the base of buildings are still alive, little stunned and panting feathery lumps. They are collected, recorded, and turned over to wildlife rehabbers. Because they don't all die right away, these not-quite-dead-yet birds are a crippling bias muddling our estimates of just how many birds die from building collisions each year.

What's Next?

The untreated glass for the stadium has already been ordered; when I spoke to Kelm-Hagen she was firm that they wanted the original transparent glass, and that the glass would begin to be installed in December 2014: " from our perspective, that clear glass design is important."

Anderson said: “This is an unacceptable loss because it’s the result of our choices for our buildings. We have an impact on our environment through our buildings. We get to make choices about the extent of the impact we have. …at some point, it just boils down to what our values are, and what we are choosing to say is what’s acceptable, and what’s not acceptable."

Audubon is now focusing on trying to get the Minnesota Governor to intervene and ask the MSFA board, half of which was appointed by the Governor, to change course. Stiteler is still optimistic: “They underestimate how much people care about birds. I’m still hopeful that we can solve this problem.”

What can you do to increase bird safety?