why do cats act the way they do when they see a bird?

Question
i am doing a science fair project on why cats act the way they do when they see a bird

Answer
Kristen,

Wow, what a good question!  The truth is that we really do not know for sure.  I cannot tell you exactly what the function of the teeth clacking behavior is.  However, the wiggling of the back end seems to be a way to get those back feet planted and rear claws out for maximum traction on take off (of the cat).  It may also have to do with triangulating the exact position of the bird so that the cat can judge exactly how much distance it needs to cover to track down the bird.  The last is speculation on my part.

The best source of cat behavior for anything is usually Dr. Michael Fox.  I was not able to find anything obviously helpful on the Internet, but you might go to the library and look at Dr. Fox's book on Understanding Cat Behavior.

Best regards... Norm.