WHY DO BIRDS TAP AT YOUR WINDOWS

This morning I have a visitor at Bell Hallow.  A little bird keeps tapping at my window.  I decided to check it out and this is what I found.  Maybe this is what they see and wanted to investigate..........who knows?

Here is another one......interesting light patterns.....

It is all very confusing to me, but maybe not to a bird.  I wonder how this translates in a birds brain?