Dr. Klem actually studied window collisions by conducting several experiments in which he hung clear panes of glass, mirrors, and picture windows adjacent to one another in a woody thicket facing an old field habitat. A strike was registered when a specimen was found beneath a window or a feather, body smudge or blood smear was found on the glass.
A copy of his study can be found on the following link: http://www.birdsandbuildings.org/docs/WB1989BirdWindowCollisions.pdf
I've also included a link to an interview he did on NPR
Windows: A Clear Danger to Birds
Right now there are still young birds around learning the ropes and unfortunately, many times it's the inexperienced birds that fall victim to window strikes. Birds also strike windows as they quickly try to escape predators, hitting glass in a moment of panic. And during spring and fall migration, window strikes increase as birds unfamiliar with the area pass through.
Window strikes are hard to totally eliminate, but there are ways to reduce them and/or reduce their severity:
- Locate feeders and birdbaths about 20-30 feet from windows so birds have time to change direction or within 1-2 feet of them so they can't gather enough speed to cause significant injury.
- Window screens will reduce injury even if a bird flies into it. Use them where practical.
- Decals like Window Alert placed on the outside of windows have had the most positive feedback from customers. Each decal contains a component which brilliantly reflects ultraviolet sunlight. This ultraviolet light is invisible to humans, but glows like a stoplight for birds. It takes multiple decals on the window surface; one stuck in the middle won't make a difference.
- Mylar reflective strips hanging loose in front of the window will move in the breeze and alert birds flying too close to a window.
- Use a yellow highlighter to draw X's on the inside of a window. The fluorescent highlighter is visible to birds, because the fluorescent ink will simultaneously absorb UV and release visible light. However it works best in sunlight, and worst in low light or on overcast days. This last suggestion comes from an experiment conducted by David Sibley, author of the Sibley Guide to Birds. http://sibleyguides.blogspot.com/search/label/bird-window%20collisions