I am in Anaheim CA. My home is adjacent to a relatively large area of chaparral hills. I agree there are likely a lot of birds that make a two-note call, but perhaps narrowing it down to this area and the fact that it calls almost exclusively after dark helps narrow it down a bit.
This sounds like it may work. I found some of the other sights mentioned but couldn't narrow it down close enough and don't have the time to listen to every bird that I am not familiar with. I'm sure that I can eliminate all game birds and raptors, but that still leaves a lot of birds.
Holy Crap! That's a hell of a stab in the dark. That is it! At the end of the song there is a little extra "chickeny" sound, just like in the link that you provided. I have only heard that portion of it one time and it actually occurred early morning after sunup. It was the only time I felt as though this bird was relatively close. Must be a much lower pitch that doesn't carry as far. That is amazing, I am so stoked to have a name to put to the sound. Can't wait to learn more about it. No wonder I've never seen one. They are incredibly well camoflauged.
