Both Cycle World and Consumer reports ran a report on deer whistles a few years ago. I never read them, but saw quotes from them in some other magazines. Both magazines hired independant research teams to look at them. The conclusion was that they don't work. Generally speaking, deer have the same range of hearing that humans do. If you can't hear them, the deer can't either. Whistles are pure hokum. Further, the reason these over sized wood rats run across our path is their natural instinct to survive. They hear a noise, or see a threat, and they instictively run at a right angle to the threat. A predator finds it harder to make a sharp turn to catch them.
Finally, what continues to bug me about this problem is that everybody complains about it but little is ever done by our "representatives" in the government. And by the way, last week another person was killed in a deer related accident just up the road from me. A man and woman were riding behind a car, the car braked and hit a deer, the motorcycle swerved to avoid the accident, ran in the ditch and killed the woman.
