There are two
things that I want to discuss about the subject of cat at a window.
First, there are some great photographs on the 'net of cats at windows
and some of the best are reproduced here under creative commons.
The
second is a quick discussion on one of the things cats do when
they
bird watch at a window - they chatter their teeth in a most noticeable
way - what is going on?

I am sure many of us have seen
the our cat at the window looking out and start chattering.
She is
automatically rehearsing the positioning and sinking of her teeth into
the neck of that bird she is watching.
The cat is a very
skilled
hunter (except for mine who prefers to sleep).