Bird watchers are concerned that U.S. Bank Stadium's signature glass facades will confuse birds, causing them to collide and die. Of particular concern is the stadium’s proximity to the Mississippi River migratory flyway. (Dave Braunger — Star Tribune/The Minnesota Star Tribune)

Three years and $300,000.

That's what the Minnesota Sports Facilities Authority (MSFA) proposes for the duration and cost of a study to determine whether the glassy new $1.1 billion U.S. Bank Stadium turns out to be a deadly draw for migratory birds.

After 30 months of construction, the ribbon-cutting for the new stadium is a week away. For the past couple of years, environmentalists concerned about bird fatalities have unfailingly attended MSFA meetings, using brief public comment periods to voice their worries.

The bird advocates are concerned that the building's 200,000 square feet of glass will confuse birds, causing them to collide and die. Of particular concern is the stadium's proximity to the Mississippi River migratory flyway.

On Friday's MSFA agenda, there is a one-paragraph item called a "memorandum of understanding with the National Audubon Society."

According to the agenda, the Vikings and the MSFA will pay $150,000 each "to design a collaborative, scientific program to design, research, observe, monitor, analyze, and assess the potential impact of the stadium on bird mortality due to bird collisions."

Lester Bagley, Vikings vice president, said workers at the stadium have seen no impact on birds so far. "But we want to be good community partners, and this is an important issue," he said.

Design of the study will begin "immediately." Monitoring will be done in 2017 and 2018 with conclusions in June 2019. "The final report will include any required possible deterrents and management techniques to reduce collisions," according to the agenda item from MSFA executive director Ted Mondale.

Audubon Minnesota spokeswoman Ashley Peters said the state and national chapters would work on the study. She said she would not answer additional questions until after Friday's meeting.

State Sen. Scott Dibble, DFL-Minneapolis, a leading legislative voice on bird concerns, said he considered the study to be "more stalling." Dibble asked why the MSFA doesn't install a protective safe film on the building — designed to alert birds to glass but naked to human eyes — and study the efficacy of that. "Then we won't have to kill any more birds in the meantime," he said.

Jerry Bahls, president of the Audubon Chapter of Minneapolis and a regular at MSFA meetings, said he awaits the details. "We are concerned that all potential areas of bird collisions are closely monitored," he said, singling out a spot on the building's north side with a wide ledge below a row of windows that is halfway up the building. "This area will be very difficult to monitor, especially if access to it is restricted."

He also expressed disappointment that the study won't start until next year and will conclude the following year, with no report until 2019. He prefers quarterly reports "to give transparency to the problem."

Bahls also suggested both a longer, more in-depth study and quicker action. He wants a longer study because the vegetation on the site won't have matured during the two-year span. The birders are concerned that vegetation reflected in the building's glass could add to birds' confusion.

In the worst-case scenario, Bahls said 1,000 birds could die annually. He urged prompt action to mitigate the problem rather than waiting out the study. Bahls also urged looking into the impact of nonfatal bird collisions, citing a study that found that only a third of residential collisions are fatal.

The bird question has hovered over the stadium throughout construction.

Initially, conservationists asked for the installation of glass with etched dots that would divert birds from the building's mirror-like facades. MSFA Chair Michele Kelm-Helgen publicly responded that the etchings would detract from the building's airy aesthetic. The building has five huge pivoting glass doors on the western wall, a signature element.

Conservationists then called for development of a transparent film to protect the birds while maintaining the translucent glass. Kelm-Helgen has talked for months about a study of such a film, but neither the film nor a study has been forthcoming.

In recent months, Kelm-Helgen shifted to say a study would be conducted to determine whether there is a problem with bird fatalities. The idea is that there wouldn't be a need for a solution unless there's a problem.

Publicly subsidized building construction is now required to have bird-safe glass. That law went into effect after the stadium legislation was passed.

Rochelle Olson • 612-673-1747

Twitter: @rochelleolson