Building collisions kill up to a billion birds every year in the U.S. Here’s how cities can fix that.

Our built environment contributes to hundreds of millions of bird deaths. Migratory birds are well adapted for long flights, using the sun, stars, and the Earth's magnetic field as navigation. But once they enter cities, it's a very different — and often perilous — story.

According to Jason Weckstein, curator of ornithology and associate professor at the Academy of Natural Sciences at Drexel University, a few simple design tweaks in cities can make an enormous difference.