This story was originally published in 2017.
Cats kill more than 1 billion birds per year in the United States. But the second leading cause of human-induced bird mortality is window strikes. There might not be much you can do if your neighbor lets Fluffy prowl your backyard, but I’m happy to report that you can do something about windows.
Many avian deaths happen at night, when birds are migrating. They may crash into high rise building windows. Evidence suggests that some birds are even attracted to lighted windows, especially if low clouds or fog disorient them.
In daylight, birds fly into windows for a variety of reasons. Sometimes the glass reflects sky. Or it may reflect outdoor scenery, so the bird thinks it’s flying into a tree or bush. Sometimes there may actually be potted plants on the window sill, giving the impression that inside is outside. Occasionally the bird can see daylight through a room that has windows on both sides, leading it to believe it can fly through the corridor.
Most of the window strikes at my house are caused when a predator flashes into the yard and birds scatter in a panic. On one occasion, it was the hawk itself that crashed into my window.
Sometimes birds are just temporarily stunned. They may fly off after a few moments. Unfortunately, not all of these birds survive. Some succumb later from internal injuries. Probably about half of window strikes result in a fatality.
And then there are those birds that intentionally attack a window. Many backyard birds get aggressive while protecting their territories. They may confront their own reflections in the glass and pummel the intruder. On these occasions, the bird normally exhausts itself before causing personal injury. I was once acquainted with a turkey who habitually attacked his reflection in shiny hubcaps.
If feeder birds crash into windows, the easiest solution is to move the feeder. Paradoxically, moving the feeder closer to the window can help. Birds within 3 feet of a window are unlikely to pick up enough speed to injure themselves. Alternatively, feeders that are more than 30 feet away are less likely to cause window strikes.
If there is a window that gets more than its fair share of bird strikes, check to see if there is an opposite window in the room that makes it look like a flight corridor. Shading the opposite window may do the trick.
Naturally, the best way to prevent window collisions is to prevent reflections. Curtains, shades, and blinds may help, but if collisions persist, it’s because the reflection persists. Window screens can cushion the blow. In extreme cases, a finely meshed net in front of the window can save lives. Make sure the mesh is too small for a bird to become entangled.
Decals and stickers work, though they have to be pretty close together — no more than 4 inches apart. Any design will suffice. Despite their popularity, decal silhouettes of hawks are no more effective than flower decals. Some decals sold in bird stores are colored in the ultraviolet portion of the spectrum. They are transparent to humans but appear brightly translucent to birds.
Vertical strips of tape stuck to the window or Mylar strips hung in front do a pretty good job of warding off birds. The goal is to put enough impediments in the way to convince the bird there’s no room to fly through, without rendering the window useless.
Still flummoxed? Science is here to help. One-way transparent film was created to allow homeowners to look out their picture windows without the neighbors looking in, but it works on birds, too. It’s not very expensive. I even found it sold on eBay. Another scientific realization is being built into many nature centers around the country. Windows are installed at a downwardly tilted angle. The view is the same from the inside, but the outside reflection mirrors the ground.
If a bird does strike the window, check its condition. If it appears stunned but otherwise undamaged, leave it alone. If there is danger lurking, place the bird in a dark box and bring it inside. This will keep it calm until it has sufficiently recovered. After 15 minutes, take it outside and remove the cover. If the bird flies away, good. If not, cover the box and wait a while longer.
Now, to repeat: The fastest, cheapest and best solution is to just move the feeder.
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