Birds pecking on your windows can get on your nerves, cause damage and pose dangers for the birds. Before you can stop the pecking, it is important to know why the birds are doing this. According to the Royal Society for the Protection of Birds, birds are territorial animals and your windows are a reflective surface. When birds see their reflection, they believe they are seeing another bird. When they see other birds so close, they believe they are a threat and start pecking to defend themselves. There are two ways to end the pecking: either make your windows less reflective or change the physical environment around your home.
Apply decals to your windows to interrupt their reflection. Any shape is OK, although cut-outs of falcons or hawks are common. Place the decals close enough together so there are no large expanses of reflective surface for the birds to see. The decals help the birds focus on the glass and avoid mistaking their reflection for an adversary.
Put a screen or tightly strung net over your window. Not all windows accommodate screens. But some sort of see-through screening or netting prevents the birds from seeing their reflection in the glass. This also creates a physical barrier so the birds are not able to reach your windows to peck on them.
Interrupt the reflection on the glass with an etching or string pattern. Have a permanent, decorative etching done, or simply attach some string to the outside of your windows. Place enough string so that birds focus on it rather than the reflection. String placed no more than four inches apart should suffice.
Soap or whitewash your windows. These covers completely eliminate the reflection, giving the birds nothing to peck at. This is ideally only a temporary measure during the nesting season.
Move bird feeders and birdbaths away from your home. Birds may become territorial over feeders and baths and attempt to defend them. People often place these items too close to their house, thus increasing the chances of birds pecking at and flying into windows. Move them to lessen the chance of birds seeing their reflection in windows.
Move plants away from windows to make your house look as little like the outside world as possible. With no plants directly in the window, birds are less likely to mistake the inside of your home for a continuation of your yard and therefore do not feel the need to defend their territory.
Close shades and blinds to cut down on the reflection of the outside world in the glass. The birds then realise that your house is a structure and not a continuation of nature.
Decals also prevent birds from flying into your windows.