Sunday evening my boys and I had an early dinner on the deck before sunset, and a pair of hummingbirds were putting on their best performance of the year so far, swooping and darting and chip-chip-chipping just a few feet from where we sat. Then I heard a sound that I'd not heard before, thought that maybe it was a branch squeaking against the garage, but a little odd, a little too high-pitched, more like a whistle, with too much air in it to be a branch. I heard it again, and so did the boys, and then again, but in the opposite direction from the garage.
It sounded like a piccolo Pete firework, like this, although not so slow. I admit that we were were plain stumped.
Yesterday evening after work I stood out on the deck, and a hummer flew up and hovered 18" in front of my face — completely marvelous greeting! Then it flew straight up about forty feet, quickly turned and shot straight down to the garden, and at the base of its dive, before it turned to arc up again, I heard the sound again, and was completely mystified.
After a lot of dinking around online, I finally discovered that what were hearing was whistling produced by air passing through feathers of the diving male bird. I also found out that if these are Anna's Hummingbirds, they do not take part in the long migration southward, and that I should continue to feed them throughout the winter. It is recommended that in cold weather, I bring the feeder in at night to prevent freezing, or else string Christmas lights around it so the ambient heat will keep the formula fluid! Oh lordy, what have I created here?! (I must admit that the little red bottle feeder with lights strung about will be quite festive.)
I think I'm in it for the long run.