xpost with bird forum:

This call has been going on tonight for quite awhile now...probably an hour. I've been listening and at one point it sounded like, whatever is calling there are two of them. At first I thought it might be an animal, but it's been going on so long from about the same location, that I'm pretty sure it must be a nocturnal bird.

The sound is a single call about a second long that almost sounds like someone is learning to whistle and doesn't quite have it a clear sound yet. This single call starts at mid-range and ascends smoothly til the end almost sounds like they've run out of air. No warble or anything and very little variation.

I live in so. new england and the call seems to be from a wooded wetlands area.

Any ideas? Or any ideas where I might look to find out?

ETA: I was poking around and found this question asked here many years ago...ignoring all the clicking, it sounds very much like what I'm hearing.