This makes perfect sense since we have deliberately bred cats for neoteny, to keep kitten like qualities.
http://www.metaphoricalplatypus.com/articles/animals/cats/cat-facts/neoteny-why-adult-cats-retain-kitten-qualities/
We’ve had many cats over the years and it’s only the newest one that we’ve gotten the “chirping” sound. She watches the squirrels on the deck or the birds at the feeder and chirps at them. I think she started it from trying to imitate the squirrels.
Heh, you may find this theory interesting:
I don’t entirely buy the “experienced hunters don’t chatter” idea. My previous (and final) cat Freckles was an experienced and talented hunter, and he made “his bird noise” whenever he saw birds from indoors. He even did it when the birds could hear him through a screen. The birds, by the way, were not spooked when they heard the noise.
Freckles and I had to part company when I figured out he was an asthma trigger for me. I put out his resumé, and he got a new job a few days later.
That’s what the Piper cats sound like.
The odd thing is they’ve just started doing it in the past two months. We’ve had Piper Cat Mark II for two years now, and Piper Cat Mark III for just under a year, and neither of them made this noise until about two months ago. They knew the pigeons were there, because they’ve watched them out of the window, but suddenly, “chitter, chitter, chitter.”
Piper Cat Mark I has never chittered. It seems to be beneath his dignity.
That is the only one that is a true cat.
Beware, the others are Pod People (Cats) or Space Aliens.
Eh, not necessarily a bad thing.
My Himalayan dust mop used to chitter at birds, chipmunks, and squirrels out on the deck, behind the glass door. Now he is so bored, he sits out there dozing in the sun, with wildlife a yard away behind him doing their thing, everyone at peace. He may surprise me someday but he’s not much of a cat. More of a catlike creature.
Why do humans ask silly questions such as “Why do Cats…”?
By now, you’d think they would have figured out that there will never be answers to these silly questions.
The discussion makes for pleasant conversation.
I prefer to simply chitter at the little birdies…
Quality time spent with our cats. 
I chitter at my cats so they know what it’s like to be the prey.
Do they react?
Are we taking about a European or African sailboat? 
Or cat does that when a butterfly is in the vicinity. He then proceeds to murder the hell out of it.
My cat was an abandoned rescue who I got at approx. 9 months. She’s 7 now, and she does this whenever watching birds out the balcony sliding door of my apartment.
I like to think that she’s simply talking smack to the birds.
It’s a nefarious plot. They’re communicating via a secret language. You are not meant to understand.
I like this theory, and I am going to keep it. I will believe that my ever so elegant, elderly lady cat has a dirty mouth, and is choosing to be, oh so rude, to the birds, and my rough and tough, ex feral is above all that.
So that next time she’s chittering in the window, and he watches, then walks away, I can believe that he’s muttering to himself, “she’s no lady”.
It will make me happy.
My cat once made a single falling tone at a robin in my backyard. A quick Googling doesn’t return any discussion about prey noises other than the “chatter.”
It was a loud “BEEEEEOOOOOOooooooo”
Cats is weird.