An expert on bird-glass collision issues recently called U.S. Bank Stadium “a classic bird killer.”

The expert, Daniel Klem, professor of ornithology and conservation biology at Muhlenberg College in Pennsylvania, spoke on bird-glass collisions and the stadium at a March meeting in Fridley. It’s one of a handful of talks scheduled in town on this divisive topic.

How deadly is the stadium? A study is underway to find out, but in the meantime, we have a few clues: Sixty dead and 14 injured birds were found at the base of the walls of U.S. Bank Stadium in the fall bird migration period of 2016, the year the stadium opened.

The count was made on intermittent days from Aug. 15 to Nov. 5 by 10 members of the Audubon Chapter of Minneapolis (ACM). Jerry Bahls, ACM president, recently spoke with me about the project.

A report titled “Mortality at U.S. Bank Stadium During Fall Migration 2016” was prepared by the ACM, Bahls said. It was presented to the Minnesota Sports Facilities Authority in February 2017.

The report compares the count of 60 dead birds unfavorably with an earlier study of bird mortality in downtown Minneapolis. For that study, from spring 2007 to fall 2009, volunteers patrolled downtown sidewalks adjacent to selected buildings.

“For comparison,” the ACM report says, “the highest mortality recorded for a single building in Minneapolis during the [2007-2009] study of bird-building collisions was 250 birds over six migration periods, averaging 42 birds per period.”

Extrapolation of the 60 documented stadium bird deaths during the fall migration of 2016 produces a potential of 360 dead birds at the stadium over the six spring and fall migrations in a three-year period, the ACM report explains.

“This underestimates true mortality,” the report says, “because it does not include birds disposed of by stadium employees, birds killed in inaccessible areas of the stadium, birds removed by scavengers and the public, and injured birds that flew off and died away from the stadium complex.

“A true count of mortality would also include bird deaths throughout the year, since collisions occur year-round, not just during migration,” according to the report.

The report can be read on the ACM website: (search the word stadium).

The 2007-2009 study was conducted by Robert Zink, at that time an ornithology professor at the University of Minnesota, and Joanna Eckles, former staff member of the state group Audubon Minnesota. Study details can be read at

Millions of birds die

While the stadium collisions have grabbed the most attention recently, it’s far from the only culprit. Each year millions of birds die in North America when they fly into glass that reflects the background, from giant skyscrapers to backyard patio doors.

Tallies of dead and injured birds found in downtown Minneapolis have been kept by ACM volunteers since 2007. Over 1,500 such birds have been found on sidewalks bordering tall buildings.

In fall 2016, 74 birds of 21 species were recorded. White-throated sparrows accounted for one-third of the total, with 21 dead. Nine were ruby-throated hummingbirds. Other sparrow species accounted for 11 casualties. Warblers numbered 27. No birds larger than sparrows were found.

Collision expert

Klem has studied the bird-glass collision issue for over 40 years. After touring U.S. Bank Stadium he called it a bird killer with an “extravagant amount of glass.”

He said in an interview that he predicted the problem when he learned of the stadium’s design. Seeing the stadium did not change his opinion. It has the potential to be even more deadly, he said.

“I walked all the way around the building,” he said. “Everywhere, all of it is lethal.”

A scientific study of bird collisions at the stadium is being made by Audubon Minnesota, collaborating with Oklahoma State University and the University of Minnesota.

Funded jointly by the Minnesota Sports Facilities Authority (MSFA) and the Minnesota Vikings, the study spans four spring and fall migration seasons. Collection of data will end this year. Findings are to be published in 2019.

Asked if any study data are available now, Elizabeth Brady, project coordinator for the MSFA, said, “No. Data will be released once the study is complete.”

Scott Loss of the Department of Natural Resource Ecology and Management at Oklahoma State University is lead scientific coordinator for the study. He earned his doctorate at the University of Minnesota. Also on the science team is Rob Blair, University of Minnesota.


Read Jim Williams’ birding blog at


To learn more

Upcoming Events

• Christine Sheppard, director of the bird glass program of the American Bird Conservancy, will speak at 6:30 p.m. April 18 at Beth El Synagogue in St. Louis Park.

• In June, Michael Mesure, executive director of Toronto’s Fatal Light Awareness Program, will be here to explain efforts to reduce night lighting in tall buildings during bird migration periods. Time and further details are yet to be set. Details will be updated when available at http://audubonchapterof

How you can help

According to the American Bird Conservancy, almost 50 percent of bird collision mortality happens on home windows. This site offers tips on how to minimize collisions: