Dear stupid pigeon.
This is called 'a window'.
It is made of glass which is a hard but transparent substance.
This means that you can see through it but not fly through it.
Every other bird in the garden understands this.
When will you get it into your birdbrain that you are not a special case?
Why not just sit in the tree and watch us eat our supper like all your feathered friends?
You will find it less painful.