This is the song of frogs, not ducks. One night a few years ago I taped a chorus of singing ranas.
Brown and about three inches long, they aren't as interesting to look at as they are to listen to. And they only sing at night which is why you won't see anything but darkness - and what may be a lightening bug.
Close your eyes and enjoy some Caribbean music...
THE BEAUTY AT FALSE BLUFF WITH CAYMAN ROCA ON THE HORIZON