Last week we were on a hillside watching the sun set, and there was a lone bird flying around. He was vocal while he was flying, when he zoomed in on the insect his wings stopped flapping and he glided to the bug. We kept hearing another sound, like a human trying to replicate a cat purr. It sounded like it was right there with us. I decided it must be an invisible insect dive bombing us! We realized, when the bird zoomed in after the insect, his still wings made this sound. It took us a few minutes to figure this out. I think he heard us discussing it and flew closer for our benefit. It was a dark bird with a prominent white bar on each wing; the common nighthawk. This was a neat experience for us. Being on the hillside, out in the country, the sound from his wings was quite distinct, near or far. I keep the National Audubon Society Field Guide to Florida book in my car for moments like this. The tell tale white bar on his wings allowed us to identify him immediately. And the sound his wings made was pretty cool.