Cardinals and Robins are very territorial birds. When birds see another of the same species in its breeding or feeding territory, it instinctively attacks the other bird.
Your house or cars windows act as mirrors to the birds.
When they are close enough to see their own reflection, they interpret this as an intruder and begin attacking or pecking at the window to chase the intruder away.
Birds Crashing or Flying into Windows
Each year, thousands of birds including Cardinals and Robins die, crashing or flying into windows.
In this case, the bird sees a refection of trees or sky and is unable to tell that the window is a solid barrier.
We as bird watchers need to take every measure possible to remedy this problem.
What do I do to stop birds from crashing, pecking windows?
Decrease the reflectivity of your windows:
Pull down your shades: white curtains or blinds can make it difficult for birds to see their reflections.
Car mirrors can be covered with paper or plastic bags and held on with rubber bands, if possible, move the car to a different spot.
Put the screens in operable windows to make them less reflective.
Consider soaping your windows for a couple of weeks during the nesting season.
Break up the reflection by hanging something, placing decorative window films, or using 1-inch-wide tape or ribbon to create vertical stripes every four inches on the outside of your windows.
Move houseplants away from the glass and close curtains over windows and sliding glass doors whenever possible.
One of our visitors, James from Ontario, said that he uses a full size 8.5 x 11 photo of a persons face. "I've tried changing the face. I tried a male and female face. I tried putting the picture on the back of a chair in the room rather than on the window. All have worked. So far the faces I have tried have all been in colour and they have filled the 8.5x11 page.
James said. Give it a try, it may work for you. Let us know if you try this and how it works out for you.
Create a physical barrier:
Build a net frame to act as a barricade by mounting fine-mesh netting (available at garden centers or hardware stores) in a rigid frame, using shelf brackets to hold the frame a couple of inches away from the window.
Install indoor-outdoor blinds on the outside of your windows.
Adhesive-backed cut-out silhouettes of hawks or falcons in flight to attach to the outer surfaces of reflective glass are sold in virtually all stores catering to naturalists and birders.
In fact, any shape will work. The non-reflective cutout helps the birds focus on the glass and, knowing it's there, avoid it.
If you're a bird watcher and feed birds, consider moving your feeders further away from windows.
While these measures won't guarantee Cardinals and Robins will stop pecking and crashing into your windows, they may minimize the behavior.
One last point This behavior is at its peak during the nesting season. For the most part, this behavior should decrease as soon as the young leave the nest.