Robins are among several bird species that are known to peck at windows. Image: Andy Hay
This behaviour is particularly prominent during the breeding season, but can also happen at other times of the year, particularly by birds such as robins and grey wagtails who hold winter territories.
There is no apparent reason to what triggers an individual bird suddenly start this behaviour, and it cannot be predicted how intense it will be and how long it will go on for.
Although most birds engaging in this behaviour do not hurt themselves in the process, many people look for ways to stop it, either because they are concerned for the bird, or because it is an irritation to themselves.
The only way to stop this behaviour is to remove the trigger – the reflection. This means putting something such as cling film or non-reflective cellophane on the outside of the window.
Once the reflection has disappeared, the attacks should stop. Newspaper can also be used, but some birds tear it off thinking that the adversary is hiding behind the paper. Curtains made of strips of plastic that flutter in a breeze may also be effective.
Often birds habitually attack only a particular window, but sometimes different windows may be attacked in sequence depending on the position of the sun. The behaviour sequence can sometimes be broken if the first window in the sequence is treated.