Okay. I am not even sure if it's a bird or maybe a bat? I am hearing this super high pitched whistle that sounds like a taxi or dog whistle at night. Sometimes it's repeated twice, most times it's a single: Fee-oh-WEE Sound. Just like you were calling your dog or a taxi. Three toned whistle: medium-low-high whistle. NOT a person, way way too high pitched, very thin and clear, almost at the non-hearing threshold (which is what made me think of a bat). NOT a frog or toad. Know all of their calls quite well. Any ideas in the birding world what bird this could possibly be? I'll try to record it if I can catch it. May not be loud enough to capture from my bedroom window in the middle of the night, but it's just started up over the last few weeks. I'm in N. San Diego county, about 7 miles from the ocean, in the very rural hilly area of Vista. Lots and lots of open land, scrub, trees. So puzzled. Have never head anything like this, and definitely NOT a human whistle.