Buildings kill a billion US birds a year. These architects want to save them

Highly transparent glass can lead to devastating collisions. But innovations in design are creating safer skylines - without sacrificing beauty

Chicago's 82-story Aqua Tower appears to flutter with the wind. Its unusual, undulating facade has made it one of the most unique features of Chicago's skyline, distinct from the many right-angled glass towers that surround it.

In designing it, the architect Jeanne Gang thought not only about how humans would see it, dancing against the sky, but also how it would look to the birds who fly past. The irregularity of the building's face allows birds to see it more clearly and avoid fatal collisions. It's kind of designed to work for both humans and birds," she said.