I hear you knocking...

A persistent wrentit pecked at its reflection in a window for days. Photo by Theresa Schultz

      It’s a case of mistaken identity; birds perceive their own reflection as a competitor. This is the time of year when most birds establish their territories, find a mate, nest and raise their young. To ensure success, they defend their territory aggressively and will attempt to drive away any bird they view as a possible rival or a threat to their young. When they see their reflection in glass, they believe they're seeing an interloper in their territory and attack the image.
      The solution is simple: Remove the reflection and the behavior will stop.
      Besides being annoying for humans, it's a huge waste of energy for the birds. That energy is better spent on feeding and nesting.
      These attacks commonly occur in spring and summer and will decrease as the breeding season progresses. A brief resurgence of the activity can occur in the fall when a change in daylight triggers a false spring reaction in the birds.
       Birds can attack their reflections with enough force to leave their imprint on the glass, but it’s not usually fatal. This behavior is different from deadly window strikes that happen when birds crash into glass in an attempt to fly through it.
      Western bluebirds, Northern mockingbirds, American robins, song sparrows and California and spotted towhees are among the birds commonly known to attack their reflections.
      Homeowners can discourage this activity by covering the outside of the window being attacked with newspaper, netting or soap to block the reflection temporarily. In addition, a couple of helium-filled Mylar balloons or just a few hanging strips of ribbon that sparkle and move in the breeze can be enough to frighten away most birds.

Happy Birding!
J.J.