As I was walking down a brushy slope this morning toward the beach, stopping to check out the birds, I suddenly heard a very loud chirp near me and then immediately I heard the high pitched chittering of a hummingbird. Assuming it was an Anna’s Hummingbird (Calypte anna), I started looking around, but could see nothing.
Then I heard another loud chirp and immediately afterwards the chittering. I was very puzzled as to how and why the hummingbird was timing his chittering calls with the loud chirp which I attributed to another bird. This happened several times before finally I was able to locate the hummingbird, an Anna’s hovering high overhead. I watched as it rose higher and higher before suddenly swooping down near the ground, whereupon I heard the loud chirp again and then the chittering as it hovered almost motionless in the air. After hovering it would then rise swiftly to a great height before diving down again. The little male kept repeating this display, but it took a while for my eyes to follow it at the bottom of its swoop because it was moving so fast.
I was amazed because I had never heard that hummingbirds could produce such a sound from the wind rushing over its feathers–especially such a loud chirp. It seemed to be directing its attention towards me which made me think that perhaps it was either a territorial display or was made in order to chase me off.
I looked up accounts of Anna’s Hummingbird, but found nothing. I just now googled the Anna’s Hummingbird and found that this was first explained in January of this year, 2008! I was shocked to learn that although it had been reported before, the last report in 1979 insisted that the sound was produced vocally. In my mind there was simply no way this hummingbird could produced such a loud chirp vocally considering it’s other high-pitched chittering vocal repetoire.
It was found that the outer feathers on its tail were spread as it reached the bottom of its dive (for 60 milliseconds, all captured on video) and that the fluttering of the trailing edge of these feathers when the bird reached speeds of 50 mph produced the sound. The only other bird that I recall producing sound with its tail is the Snipe. I also remember the so called “Bull Bats” or Common Nighthawks (Chordeiles minor) making a very loud sound as they used to dive at me on the plains of Kansas and Texas. I think it is claimed that this sound is made by the outspread wings, but I wonder if any part of it is made by the tail feathers.
One thing that is surprising to me is that with all the Ornithologists and amateur bird watchers this wasn’t explained before now. It will be interesting to see if this behavior is found in other hummingbirds.
After the male tired of his flight display, he landed on a bush and spread the violet feathers around its neck so wide that it looked like a great lion’s ruff—beautiful!