Here's an interesting tidbit:

I was just on the phone with my sister and she told me that over the last two months there's been a small hawk with bells around their Claremont neighborhood. They live up against Mount Baldy there in Claremont and this bird is often heard and occasionally seen. They don't know what species only that it's "compact" about 10 inches high (estimate!) and wing span of maybe 18 inches (estimate!). Her husband doesn't think it's a Coops. He said he's a little familiar with that species. But who knows?

Wish I could give more information but if you know of anyone who's lost their bird in the last three months in the Pomona/Claremont area I could try to get you in touch.