Although birds may accidentally fly into windows, sometimes they may appear to deliberately attack them and this behaviour can seem quite alarming.
It is not fully understood why birds peck at windows but the behaviour occurs more often during breeding season and is believed to be territorial. Aggressive species such as robins tend to exhibit this behaviour more often.
One theory put forward is that when a bird sees its reflection in a window or other shiny surface it assumes it is a rival and will attack it in an attempt to drive it away. As well as pecking at the window the bird may rake it with its talons, fly against it or beat it with its wings.
Birds do not usually hurt themselves while they are attacking a window but they may exhaust themselves in the process and many people find the behaviour disturbing.
We have some advice on what you can do to prevent birds flying into windows and the same tips can help with stopping birds deliberating attacking a window. If they are attacking a number of windows then target a window early in the sequence and the behaviour cycle should be broken.
It may appear that birds are attacking windows outside of breeding season. This behaviour is usually observed in the autumn and winter by members of the tit family.
In this case birds are usually looking for spiders and insects buried in the window frame. They may also be attracted to the linseed or fish oils that can be found in some putty. Using a synthetic putty should prevent this behaviour or you could cover the putty with masking tape or brush it with a compound containing aluminium ammonium sulphate.