The design of the new Minnesota Vikings stadium drew awe for its futuristic design with a see-through roof and 200,000 square feet of clear and reflective glass. But now the park is drawing some sharp criticism from local environmental and animal rights advocates because all that glass appears to be a deadly hazard for the birds migrating through Minneapolis.

Over a course of 11 weeks, beginning in August, volunteers from three conservation groups made laps around the newly-opened US Bank Stadium every day and said they found 60 dead birds and 14 more stunned from flying into the glass. Based on the findings of just one migration season, they estimate that as many as 360 birds could be killed as a result of the glass coliseum in a three-year period.

“We knew that the glass would be highly confusing to the birds," Jim Sharpsteen, one of the volunteers, told City Pages. "They see a reflection of a blue sky in the glass, they think it's a blue sky. They see reflections of trees, they think they can land in those reflections of trees. This confirmed what we already believed would be bad.”

In comparison, the previous record of highest mortality from bird-building collisions for a single building in Minneapolis was an average of 42 birds per migration period, according to a three-year study conducted in 2010.

The three groups, Audubon Minneapolis, Minnesota Citizens for the Protection of Migratory Birds, and Friends of Roberts Bird Sanctuary, presented their report at a Minnesota Sports Facilities Authority meeting on Friday, hoping the agency will make appropriate changes, which includes bird-safe treatments to the glass on all sides of the stadium.

Advocates from the Audubon Society first raised the issue of bird collisions two years ago, when the coliseum was under construction. The agency responded saying that it did not have the budget for special glass, which would cost an estimated $1.1 million extra, as The Christian Science Monitor reported in 2014.

"One of the design goals was to create a building that was more connected and integrated with the community than the Metrodome had been," MSFA chairwoman Michele Kelm-Helgen said in a news release at the time. "The ability to see in and out of the stadium was what led us to the design that included the [translucent plastic] roof and operable doors on the downtown facing wall."

The Minnesota Vikings stadium is far from the first glass architecture to have drawn controversy for causing bird collision fatalities. Several buildings in Washington, D.C., including the D.C. Court of Appeals and TechWorld Plaza, have long been on birders’ radar as a “fatal attraction” to millions of migratory birds. After intervention by activists, the top bird strike site in the US capital, Thurgood Marshall Federal Judiciary Center, now dims its light during the migratory seasons.

Recognizing the popularity of using glass in architecture design, a non-profit group American Bird Conservancy in 2015 released guidelines for designing bird-safe buildings, which include using exterior shades, angled glass, or tape to reduce the impact.

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While periodic reports of isolated incidents have gained a fair amount of public attention, there is a lack of awareness of just how common bird collisions are, advocates say. According to a 2005 study by the USDA Forest Service, an estimated 500 million to over one billion birds are killed annually in the United States due to collisions with manmade structures, including buildings, vehicles, and power lines.

“[Most people] are still unaware that bird strikes are not an isolated event, but rather part of a global problem that results in significant numbers of bird deaths,” Anne Lewis, president of City Wildlife that runs a monitoring program “Lights Out DC,” told Quartz in 2015. “Everyone who has ever heard or seen a bird strike thinks of it as a very sad, isolated event, not worthy of any corrective action.”