This is the time of year in the United States when millions of birds are completing their migrations north from their winter homes. It is also a dangerous time of year, especially for birds flying through major cities. Bird scientists, ornithologists, estimate more than 100 million birds die each year by flying into buildings. Several North American cities are trying to make their skylines more bird-friendly.

At the Field Museum of Natural History in Chicago, conservation ecologist Doug Stotz pulls open a wide drawer in a research storage part of the museum. It is filled with dead birds. Each has a small tag tied around its legs, listing the type of bird and when it was found. All of these birds died by flying into the large windows at Chicago's McCormick Place Convention Center. "The big families are sparrows, which these represent. That is a sparrow, these are sparrows. And, the warblers, which are mostly these yellow guys," he says.

Field Museum scientists have been collecting dead birds from McCormick Place for about 25 years. They've picked up nearly 30,000. Mr. Stotz says most die during the migration periods in the spring and fall. Chicago's parkland along Lake Michigan makes it an inviting pit stop for birds following the lake on their migration routes. But lights from some of the city's most recognizable buildings somehow confuse the birds and create a fatal attraction. "Whether the glass is reflective or transparent, birds do not see it. They do not see it as something stopping them. It is sort of like when you have a newly-cleaned sliding glass door and you do not know that it is closed, you might walk into it," he says. "Birds never know that it is closed."

For the last two years, Mr. Stotz and his colleagues have been visiting McCormick Place every day during the migration season, noting how many birds were found each day, and whether the building's lights had been on or off the previous night. "We found that when the lights are turned off at McCormick Place, it cut the number of birds hitting [the building] by more than 80-percent," he says.

Chicago is not the only city whose skyline presents a migratory hazard. Toronto, another lakefront city, estimates 10,000 birds a year die hitting its buildings. Mike Mesure first heard that in the late 1980's. "I had never heard of this issue. I had to go down and check it out. I got up bright and early one morning, went downtown, pulled over the car, opened the door and there was a bird. And another bird. And another bird. I was shocked," he says.

He has helped create Toronto's Fatal Light Awareness Program, or FLAP an effort to work with building managers and reduce the number of dead birds on downtown streets. "Basically it was a series of steps we were recommending buildings comply to in accomplishing light reduction," he says. "By doing so they would save birds' lives and also save hundreds of thousands of dollars in energy costs and emissions into the atmosphere to produce hydro (electricity) and so forth. All of this combined is a win-win situation."

Mr. Mesure says about 100 buildings participate in his program. Additionally, FLAP volunteers roam downtown streets before sunrise during the migration seasons, collecting injured birds. It has also established six locations throughout the city where anyone can take an injured bird, and a FLAP volunteer will pick it up. "The beauty of that is it makes people feel good," he says. "They feel like they are doing something to help the bird, and they love to participate."

Aside from windows, another bird hazard in Chicago is decorative lighting atop many tall buildings. About 20 buildings are participating in a two-year old program called, "Lights Out Chicago." It asks outdoor lighting be turned off after 11 o'clock at night, when migration tends to be heavier.

Program coordinator Jane Pollock says the engineer of one building which turns off its rooftop lighting at night has noticed a difference. "He said that since the lights have been turned out there, they have seen very few dead birds," she says. "There was one [bird] up there at the time we were there at the height of the migration period. He said you might see five or six in one week. Previously, we had information from several people that they would take shovels-full of birds off that roof." Ms. Pollock hopes the Field Museum's study suggesting dark buildings appear to be safer buildings to birds will encourage more participation in the 'Lights Out" program.