Cats are number one threat to birds in the wild. Can you guess the number two threat?

It’s buildings.

Every year, hundreds of millions of birds are killed flying into manmade structures. It’s not because their sense of direction isn’t what it should be. The problem is glass. Sometimes it’s simply invisible to them. Other times it reflects their habitat, and birds mistake the reflection of a tree branch for an actual perch.

Unfortunately for our feathered friends, the built environment has incorporated more and more glass over the past few decades. The American Bird Conservancy, which is working to educate the building industry about bird-friendly design, would love to see architects and designers use less of it. But short of that, said Christine Sheppard, director of the Conservancy’s glass collision program, “There are lots of different ways that you can make buildings bird-friendly. Retrofitting is definitely possible.”

Bird safety is increasingly considered at universities and zoos, Sheppard said, and “there are at least six buildings in Salt Lake City that have earned the LEED credit for reducing bird collisions.”

Here are 10 ways — some simple — to make buildings safer for the birds around them.  

1. Place glass behind some type of screening, like the de Young museum in San Francisco and Cooper Union college in New York City have done.
2. Add decorative grilles or shutters to windows.
3. Install exterior, motorized screens/shades. (Bonus: They help control heat and improve security.)
4. Create a pattern in window glass with Tempera paint using a stencil or brush.
5. Use bird-deterring window films. CollidEscape, for example, looks transparent from the inside but opaque from the outside. WindowDressing makes patterned films.
6. Put lightweight netting or removable screens over windows.
7. Use simple decals.
8. Add Acopian BirdSavers, which are essentially curtains of evenly spaced cords that hang in front of windows.
9. Remove large plants from glass atriums. Birds may go straight for them.
10. Replace regular glass windows with fritted glass, which usually has subtle dots or lines. It’s more visible to birds and also reduces solar heat inside.