Employees at HealthPartners in Bloomington started seeing the bodies of songbirds on the building's walkways and grounds soon after it refaced its headquarters with energy-saving glass.

Now, as Audubon Minnesota's newest recruit to its "Lights Out" campaign, HealthPartners is ready to darken its building from midnight to dawn during spring and fall migrations to avoid drawing birds that might fly into windows and die.

"We have already turned off all the exterior decorative lighting as well as the atrium lighting,'' said Peg Younghans, director of corporate facilities for HealthPartners. The company's all-night on-call nurses also have been moved from upper floors to the second floor so the upper floors of the 14-story building can be cleaned and darkened by midnight instead of by 2, 3 or 4 a.m.

"It's a great opportunity to help the birds and to help energy consumption for HealthPartners,'' Younghans said. She estimates that the company will significantly reduce light use per week per floor. "It's going to be huge.''

The critical times for the birds are during their migrations: The spring migration runs from March 15 to May 31, the fall one from Aug. 15 to Oct. 31.

During those times, small songbirds, including warblers and thrushes, migrate at night, guided by the stars, the horizon and rivers, said Joanna Eckles, Lights Out coordinator for Audubon Minnesota. It's believed that the light from buildings and communication towers draws birds off course -- especially when clouds are low and birds tend to fly lower, Eckles said.

Once drawn to the lights, birds end up circling in the glow, having difficulty finding the way out. Often they crash into buildings or drop to rooftops or the ground from exhaustion, she said.

The 'Lights Out' movement

To prevent this, the Audubon Society this year is expanding its effort to enlist new buildings in its Lights Out campaign.

About 29 buildings in Minneapolis, St. Paul, Bloomington and Rochester have joined the effort since the program began three years ago. Eckles' goal is to double that number over the next two years, taking aim at the tallest and brightest buildings.

She asks building managers to turn out the exterior architectural lighting that defines the outer shape of the building. "A lot of times that is really bright on the peak of the building,'' she said. The interior lighting on upper floors is the next target. Darkening upper floors first sometimes requires a change in cleaning schedules.

Wells Fargo was the first in Minneapolis to darken its tower for the migrations. "It's definitely noticeable,'' Eckles said.

Another Minneapolis landmark, the IDS Tower, turns off all outside lights around the top perimeter of the building during the migrations. Building owners' groups in Minneapolis and St. Paul endorse the program.

"The feedback we have gotten is that not only the building managers but the tenants are very enthusiastic about it,'' said Kent Warden, executive director of the Greater Minneapolis Building Owners and Managers Association.

Toronto was the first city to get serious about preventing birds from crashing into buildings. New York has joined the effort. New to the program this year are Detroit and Boston, Eckles said.

Tracking the numbers

To estimate the number and kinds of birds being killed in crashes with buildings, Audubon volunteers walk defined routes in downtown Minneapolis and St. Paul every morning during the migrations. They pick up any birds they find, dead or alive, and note the time and location. Live birds are released outside the city and dead birds are taken to the Bell Museum at the University of Minnesota. HealthPartners also sends dead birds to the U.

The top six species showing up in the sweeps are the white-throated sparrow, the Nashville warbler, the Tennessee warbler, the oven bird, the dark-eyed junko and the common yellow throat. "Those six species make up 60 percent of the birds we find,'' Eckles said.

It's difficult to get an accurate count of the birds killed because they get picked up by cleaning crews or by scavengers such as crows, and they fall on rooftops or ledges and never make it to the ground to be counted.

Nationwide, estimates range from 100 million to 1 billion birds a year that die because they fly into buildings, said Bob Zink, curator of birds for the Bell Museum at the U. "Basically, it means we have no idea.''

To arrive at a better estimate, the Bell Museum counts and catalogs each bird brought in. Over the past two years, the number has come to about 700 -- and in each case the cause of death was head injuries.

Zink keeps a permanent record of the birds by sex, age, the time and location where they were found and whether their stomachs held food when they died. He also saves a wing or tissue from each bird.

"If the birds were discarded, somebody could always argue that you didn't get 12 Tennessee warblers, you only got one,'' Zink said.

Eventually the records will lend new understanding of which buildings are causing the most problems and whether the birds most likely to die are younger or older, male or female, hungry or not, Zink said.

Laurie Blake • 612-673-1711