Years in the making, the three-year study of bird fatalities at the glass palace that is U.S. Bank Stadium becomes public. (The Minnesota Star Tribune)

Seven years ago, instead of building a new football stadium that is safe for birds, the Minnesota Sports Facilities Authority came up with a series of excuses not to do so.

At that time, the cost for bird-safe glass for the entire stadium would have added only 0.1% to the $1 billion cost of the stadium (half paid by taxpayers). Early design discussions had included bird-safe glass, consistent with the wishes of the community. But then MSFA changed its mind.

Despite intense public pressure, including a letter from the Department of Natural Resources, a resolution from the Minneapolis City Council, a petition with tens of thousands of signatures (including many football fans) and protests from bird conservation groups, the MSFA refused to listen.

Instead of building a bird-safe stadium, the MSFA and Vikings paid almost a third of the $1 million cost of bird-safe glass to fund a study of bird mortality.

Now that study is out and shows a significant number of migrating birds are killed by the stadium glass every year, just as the Audubon Chapter of Minneapolis and other groups predicted and found in their own study released in 2017. The stadium's highly reflective glass in the Mississippi Flyway, a major migration corridor used by millions of birds twice a year, virtually guaranteed that the stadium would rank among the top bird-killing buildings in the city, as the new study confirms.

The study found that U.S. Bank Stadium had the third-highest fatality estimate of 21 downtown buildings surveyed. At least 111 bird deaths occurred annually at the stadium. Estimated fatality rates at the stadium and the other three top buildings exceeded all other buildings in the study, and also exceed death rates at most U.S. high-rise buildings (based on a previous study of 11 cities). The study's conclusions "stress the need to prioritize mitigation strategies related to reducing window collisions (e.g., window films and markers) versus those reducing urban vegetation."

Much has changed since MSFA officials refused to build a bird-safe stadium. The news for birds has become even more grim. Earlier this year, a study by the Cornell Lab of Ornithology named the Twin Cities one of the worst urban areas in the country for migrating birds. Last month, a study published in the journal Science found that wild bird populations in the continental U.S. and Canada have declined by 3 billion birds (almost 30%) since 1970.

And a new report from National Audubon Society estimates that two-thirds of North American birds face extinction because of climate change. At the same time, awareness of the threat to birds posed by glass has grown and solutions have been developed to make glass less deadly, including film developed by 3M.

Some people wonder why we should care about an estimated 111 birds killed at the stadium every year, but the study acknowledges that the actual number is likely higher. And taking these birds from the breeding population has exponential effects, greatly contributing to staggering bird declines already documented.

Minimizing the importance of any bird deaths in the Mississippi Flyway also misses the point that these deaths are entirely preventable at a time when we must protect birds to protect our environment.

Besides window collisions and climate change, birds face many other threats, including habitat loss, roaming cats and plummeting insect populations, birds' primary food source. These growing dangers and the alarming decline in bird populations make immediate protection of migratory birds imperative, particularly in the Mississippi Flyway.

When Minnesota's bird-safe building requirements first took effect, U.S. Bank Stadium became the last building funded with state bond money that was not required to use bird-safe glass. The intent of this wise legislation is "to limit the risk of built environments to birds, with special attention to the highest-risk conditions."

MSFA's own study now confirms that U.S. Bank Stadium is one of the highest-risk buildings in Minneapolis. It's time for current MSFA officials to undo the bad decision made by their predecessors and fix the glass.

Steve Greenfield is president of Friends of Roberts Bird Sanctuary. Wendy Haan is co-founder of Minnesota Citizens for the Protection of Migratory Birds. Jerry Bahls is past president and current board member of Audubon Chapter of Minneapolis.