What's the Handprint Rule?

The definitive research on birds colliding with windows --carried out over three decades by Professor Daniel Klem, Jr., at Muhlenberg College -- has determined that small birds will attempt to fly through any opening larger than 4 inches wide or 2 inches tall.  That's about the size of an adult handprint.

Thus, when creating "visual noise" on or around a window, be sure that the openings are no larger than a handprint.

See the Information section for Professor Klem's research reports.

Handprint design courtesy of Marglyph Berrier, www.artglyphs.com

This Cardinal demonstrates that the paper taped to the middle of the window -- intended to be a warning to birds -- does nothing to deter the bird from flying into the window space around the paper. As long as a bird can see that there is adequate room for a flight path, birds are likely to fly into the window to get to the reflected trees or other bird attractions.

Thanks to Heidi Trudell  for the photograph.