Over the past few weeks, Robb and I had been hearing a strange, loud, and intermittent "chirp" sound, out in the back yard. We found this sound very hard to pin-point, and I think that was driving Robb crazy. It seemed to move around the neighborhood, and it seemed to come from somewhere just above our heads.
And then the other day, I noticed a little female Anna's Hummingbird sitting on a tiny branch. I'd hear the chirp, which would be immediately followed by the "annoyed" sound of hummingbird chatter. CHIRP ... chatter ... CHIRP ... chatter ... CHIRP ... chatter. Over and over again.
I mentioned this to Robb, who did a little digging around on the internet, and found out that what we had been hearing were the mating flights of the male Anna's Hummingbird.
When the males are courting the females, they fly up to a hundred feet in the air. (Let's just say that again: a creature who weighs less than a nickel, flies a HUNDRED feet in the air.) And then, they swoop down in a J-shaped arc, at about FIFTY miles-per-hour.
And at the curve of their swoop, they flare their tail-feathers for the briefest moment, and the wind whipping over the bird's two outer tail feathers creates a loud chirp sound. This is akin to blowing over a kazoo. Female hummingbirds, we are told, find this extremely alluring.
Once Robb mentioned this, I remembered hearing about this research, which was done using high-speed cameras at the Albany Bulb. Students from the University of California at Berkeley set up a stuffed female hummingbird, and filmed the males who vied for her affection. The researchers then (goodness knows how) caught a couple of hummingbird, and trimmed or removed their outer tail feathers (which are not need for flight, and grow back in a little more than a month). They then documented that these particular birds could no longer make the chirp sound.
Further studies were done in wind tunnels, to determine that the birds needed to reach huge speeds, before their feathers would create this peculiar (and LOUD) sound.
We're now learning to locate diving male hummingbirds, once we start hearing the chirp sound. It's actually hard to keep an eye on them for the entire flight pattern. They fly so high up, that they're almost gone from view.
If you want to read more about this fascinating little bird or hear sound clips, click here.
(Photo by Christopher J. Clark and Teresa Feo/UC Berkeley)