Right now, that’s the sound I hear every night (and most mornings, too). In my mind, it’s really kind of a peaceful piece of the evening. It’s the sound of all the cicadas in the trees. I’ve noticed it a lot more this summer for two reasons: 1. I had a friend visit me from the west coast and the sound freaked him out. Southern California doesn’t have big (or any) populations of cicadas, so it’s not a sound with which he was familiar. 2. After spending part of my summer back on the west coast, I was more keenly aware of the night sounds when I came back.
Anyway, at night, I quite enjoy listening to all those guys drone on and on out there in the trees. I’m still in the process of figuring out which species we have around here (it is likely more than one kind), but I can tell you that it really is the guys who are doing all that droning.
“But why won’t they shut up?” you ask.
Well, desperate times call for desperate measures. Why are they desperate? They don’t have mortgages to worry about. They do, however, want to find mates. If you’re an animal that moves around at night, what are good ways to track down a possible mate? Vision isn’t so good. Chemicals work (moths are good at using those). Sound can also be effective. The cicadas are out there trying to track down mates. Tonight, when they’re doing all their droning, try to move in close to hear just a single cicada instead of the whole group. The energy that a single male puts into his song (or irritating drone) is the only way that he can find a mate. He puts himself up on a branch and calls and calls until some female tracks him down.
I’m no cicada expert, but I’m doing some more digging because they’re fascinating. Different species have different kinds of droning and the females are quite capable of picking out the right sound. Apparently, there are two components of the cicadas song that are important in this discrimination: timing and frequency. The really cool part is that these differences are important at different times!
Doolan, J.M. and D. Young. 1989. Relative importance of song parameters during flight phonotaxis and courtship in the Bladder Cicada Cystosoma saundersii. Journal of Experimental Biology 141: 113-131.
These researchers found that frequency (pitch) components of the sound are important features that females use to localize a male in the first place. In order to find an appropriate male (one of the same species), she’s got to be able to pinpoint him in a very noisy environment. She’ll move towards males who produce sounds at the correct pitch. But once the female arrives in the right spot, pitch doesn’t seem to be as important. At the time of arrival the temporal qualities of the song (the repetition rate) seem to be more important in courtship (and female choice). Courtship? Yes! These cicada ladies do appear to be making choices about which male will be their mate. There’s so much cool stuff going on in their little insect brains.
Wannhh wannhh wannhh wannhh really is the sound of desperate males. They’re out there on the trees trying to produce a sound that is loud enough and at the right pitch to draw in a female out of the dark. Think about how loud those cicadas get, too. That’s a lot of males (and therefore a lot of competition). Those guys are droning their little hearts out to try to draw in those females. So tonight, when they’re out there, go watch them and compliment a male or two on his sounds to give him a little confidence boost.