As has Jim, I've done some telescope work in the pines and have also been nocturnally audio-recording frogs, birds, and insects routinely for the past few years. Not a single incident to report here. When actually approached, it has only been by rangers checking to see what I was up to. That's not to say one should not use common sense and practice caution; for one, I always let somebody at home know where I plan to be. I must confess, though; when back in the middle of nowhere and seeing headlights slowly approach from far away, a person doesn't feel quite as comfortable as he or she might while encountering a stranger during daylight.