I lived in Northern New Jersey which his over run with deer. Yes, New Jersey. In my experience with the many deer encounters that I have had, it is true that they are mostly active during dawn & dusk when they are on the move, and especially durring the rut in the Fall! I have seen deer bolt right in front of me when they could've simply stayed put. I don't know what it is that makes them do that. I wouldn't call them dumb but there is some triggering mechanism built into them that throws caution to the wind and they just want to bolt. I agree with others in that you need to have a good idea that when you are in an area that holds deer you've got to have your wits about you and pay attention. For me that means going slower than I usually would just in case I have to hit the brakes hard or make an evasive move. But if they decide to jump out in front of you I don't think loud pipes or high pitched deer frequency devices that we affix to our bikes are really going to save us IMO.