The results of a $300,000, two-year study examining how many bird deaths have been caused by U.S. Bank Stadium have been revealed.
The study was commissioned after objections to the giant glass facade at the northwest end of U.S. Bank Stadium were raised by wildlife groups prior to its construction.
The fear was that the reflection from the glass would causing migrating birds to collide with the building, leading to an inordinate amount of deaths. The objections didn't lead to a change in the design, but did prompt the Minnesota Sports Facilities Authority and the Minnesota Vikings to agree to fund a study into its impact.
The study found that over spring and fall migration periods, as well as the early summer period of both 2017 and 2018, a low-end estimate of 1,000 birds were involved in fatal and non-fatal collisions with 21 buildings included in the study in downtown Minneapolis.
Of those, 780 of the collisions resulted in a bird's death, and of those, 159 of the fatal collisions happened at U.S Bank Stadium, which also had 70 non-fatal collisions, meaning it accounted for an estimated 22.9 percent of all bird-building collisions out of the 21 structures surveyed.
In total, four buildings in downtown Minneapolis including U.S. Bank Stadium accounted for 74 percent of bird collisions and 68 percent of bird fatalities. The report does not mention the other three buildings by name.
Given that the study wasn't year-round, it estimates that U.S. Bank Stadium is involved in 111 bird deaths annually. The other three high-fatality buildings range in their annual death rates from 76 to 216 – so U.S. Bank Stadium isn't the most deadly building in Minneapolis for birds.
Of the bird deaths observed at U.S. Bank Stadium, 52 percent happened on the northwest glass face, with 17 percent on a glass surface on the southwest facade, and 11 percent on a glass surface on the northeast facade.
"Our results suggest management approaches that can reduce bird collisions at both new and existing buildings," the study concludes. "Reducing numbers of collisions and numbers of species colliding should be achievable by reducing light emission at night, reducing the area of untreated glass, and avoiding the use of vegetation near glassy surfaces."
"Our results for U.S. Bank Stadium suggest that a major reduction in collisions can be achieved by focusing mitigation on one or more particularly problematic spans of glass"
In a joint statement issued on Wednesday, the MSFA and Vikings said it would be "further evaluating" what could be done to reduce bird deaths, and while they haven't gone so far as to agree to altering the surface of the glass to reduce reflections, it did say it would consider using "lights out" guidelines during migratory seasons suggested by the National Audubon Society.