Treacherous Glass: Bird Collisions with Windows

by Jan Thornhill

Ruby-crowned Kinglet (Dania Madera-Lerman)

It’s October and fall bird migration is ongoing. Though most warblers have already crossed our southern neighbour’s border, many other songbirds, as well as shorebirds, ducks, and raptors, are still moving south.

Migration is fraught with danger and hardship for birds. Many fly thousands of kilometers, following flight paths established by their ancestors millennia ago. But things have changed. Suddenly (at least in millennial terms) there is a new hardship: cities filled with glass-windowed buildings have been built smack in the middle of some of these flight paths. And these glass-windows are lethal, even to the healthiest bird.

A Ruffed Grouse victim

Migration season isn't the only time that birds are killed by glass—it happens in all seasons, and it happens everywhere. In the United States alone, it’s estimated that from 100 million to one billion birds die each year from window collisions. Put another way, that’s 1-10 birds per building per year. These are shocking numbers.

As a human, I have to say I’m quite fond of windows. They allow me to look outside, which keeps me from feeling imprisoned while I’m stuck at my computer inside. Nice for me, but not good for birds.

Birds, such as doves, that have powder down feathers sometimes leave behind
ghostly reminders of their collisions with glass. (Beth Woodrum, Wikicommons)

Though birds have amazing visual capabilities—they see more colours than we do and can process what they see faster—hard, transparent glass is not something they recognize as a barrier. What they do recognize are trees, water, dark spaces. If they see a tree reflected in a window, they assume they can navigate through its branches. A group of potted shrubs in a glassed-in atrium looks like the perfect place to perch and have a rest. The reflection of a fountain is a drink of fresh water. A dark space indicates a safe “fly through” zone. Birds don’t slow down when they see these things, so when they hit windows, they hit them hard. About half will die immediately, usually from brain hemorrhages. Others can have broken wings or beaks, concussions, or other injuries that make them easy victims for predators.

In some cities, gulls have learned to patrol high incident areas
to scavenge recent kills and injured birds. (Wikicommons)  

So What Can Be Done? And What Is Being Done?

Reflections can be blocked with physical barriers, such as netting or shades. Glass can be etched or otherwise marked to create recognizable “no-fly” zones. New panes have been developed that have external patterns that birds can see from the outside, but that are invisible from the inside. Here is great document put together by the Bird Conservancy of America that has lots of pictures of amazing architectural solutions for bird-safe buildings.

Double-whammy corner windows show foliage reflected in one window
as well as a clear view of trees and sky through a second window. 

Largely due to grassroots organizations such as Toronto’s FLAP and the American Bird Conservancy, businesses and government are beginning to respond. Researchers, basing their work on avian vision and behavior, have been coming up with novel solutions for building “bird-safe” structures and for modifying existing problem areas. Governments, including those of Toronto and New York State, are gradually coming on board, by putting in place legislation requiring new buildings to be bird friendly.

What You Can Do at Home:

Single decals like this DON'T work. They're only effective
if you cover the window with them.

• place bird-feeders and bird baths half a meter or less from windows
• move houseplants out of the sight line of birds
• hang string or ribbon vertically 4" apart in front of windows
• decorate windows with patterned window film (i.e. FeatherFriendly's DIY tape) 
• more solutions from FLAP

Children's Books About Bird Migration:

• Is This Panama: A Migration Story (Owlkids): Jan Thornhill & illustrator Soyeon Kim—my 2013 book's main character, Sammy, meets office tower windows (and other migrating characters!) on his epic first journey from the Arctic to his wintering grounds in Panama

• Moonbird: A Year on the Wind with the Great Survivor B95  (Farrar, Straus and Giroux):  Phillip M. Hoose—award-winning book about the "world's most celebrated shorebird" illustrated with photographs 

• The Long, Long Journey: The Godwit's Amazing Migration (Lerner): Sandra Markle & illustrator Mia Posada—follows a young godwit from hatching to first long-distance migration, with beautiful watercolour/collage illustrations

• How Do Birds Find Their Way (Let's-Read-and-Find-Out Science 2) Roma Gans & illustrator Paul Mirocha—facts about bird migration with well-labelled species and maps